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• NoHostAvailableException With Cassandra & DataStax Java Driver If Large ResultSet

  - by hughj

  The setup: 2-node Cassandra 1.2.6 cluster replicas=2 very large CQL3 table with no secondary index Rowkey is a UUID.randomUUID().toString() read consistency set to ONE Using DataStax java driver 1.0 The request: Attempting to do a table scan by "SELECT some-col from schema.table LIMIT nnn;" The fail: Once I go beyond a certain nnn LIMIT, I start to get NoHostAvailableExceptions from the driver. It reads like this: com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: /10.181.13.239 ([/10.181.13.239] Unexpected exception triggered)) at com.datastax.driver.core.exceptions.NoHostAvailableException.copy(NoHostAvailableException.java:64) at com.datastax.driver.core.ResultSetFuture.extractCauseFromExecutionException(ResultSetFuture.java:214) at com.datastax.driver.core.ResultSetFuture.getUninterruptibly(ResultSetFuture.java:169) at com.jpmc.es.rtm.storage.impl.EventExtract.main(EventExtract.java:36) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120) Caused by: com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: /10.181.13.239 ([/10.181.13.239] Unexpected exception triggered)) at com.datastax.driver.core.RequestHandler.sendRequest(RequestHandler.java:98) at com.datastax.driver.core.RequestHandler$1.run(RequestHandler.java:165) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) Given: This is probably not the most enlightened thing to do to a large table with millions of rows, but this is how I learn what not to do, so I would really appreciate someone who could volunteer how this kind of error can be debugged. For example, when this happens, there are no indications that the nodes in the cluster ever had an issue with the request (there is nothing in the logs on either node that indicate any timeout or failure). Also, I enabled the trace on the driver, which gives you some nice autotrace (ala Oracle) info as long as the query succeeds. But in this case, the driver blows a NoHostAvailableException and no ExecutionInfo is available, so tracing has not provided any benefit in this case. I also find it interesting that this does not seem to be recorded as a timeout (my JMX consoles tell me no timeouts have occurred). So, I am left not understanding WHERE the failure is actually occurring. I am left with the idea that it is the driver that is having a problem, but I don't know how to debug it (and I would really like to). I have read several posts from folks that state that query'g for resultSets 10000 rows is probably not a good idea, and I am willing to accept this, but I would like to understand what is causing the exception and where the exception is happening. FWIW, I also tried bumping the timeout properties in the cassandra.yaml, but this made no difference whatsoever. I welcome any suggestions, anecdotes, insults, or monetary contributions for my registration in the house of moron-developers. Regards!!

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• Creating thousands of records in Rails

  - by willCosgrove

  Let me set the stage: My application deals with gift cards. When we create cards they have to have a unique string that the user can use to redeem it with. So when someone orders our gift cards, like a retailer, we need to make a lot of new card objects and store them in the DB. With that in mind, I'm trying to see how quickly I can have my application generate 100,000 Cards. Database expert, I am not, so I need someone to explain this little phenomena: When I create 1000 Cards, it takes 5 seconds. When I create 100,000 cards it should take 500 seconds right? Now I know what you're wanting to see, the card creation method I'm using, because the first assumption would be that it's getting slower because it's checking the uniqueness of a bunch of cards, more as it goes along. But I can show you my rake task desc "Creates cards for a retailer" task :order_cards, [:number_of_cards, :value, :retailer_name] => :environment do |t, args| t = Time.now puts "Searching for retailer" @retailer = Retailer.find_by_name(args[:retailer_name]) puts "Retailer found" puts "Generating codes" value = args[:value].to_i number_of_cards = args[:number_of_cards].to_i codes = [] top_off_codes(codes, number_of_cards) while codes != codes.uniq codes.uniq! top_off_codes(codes, number_of_cards) end stored_codes = Card.all.collect do |c| c.code end while codes != (codes - stored_codes) codes -= stored_codes top_off_codes(codes, number_of_cards) end puts "Codes are unique and generated" puts "Creating bundle" @bundle = @retailer.bundles.create!(:value => value) puts "Bundle created" puts "Creating cards" @bundle.transaction do codes.each do |code| @bundle.cards.create!(:code => code) end end puts "Cards generated in #{Time.now - t}s" end def top_off_codes(codes, intended_number) (intended_number - codes.size).times do codes << ReadableRandom.get(CODE_LENGTH) end end I'm using a gem called readable_random for the unique code. So if you read through all of that code, you'll see that it does all of it's uniqueness testing before it ever starts creating cards. It also writes status updates to the screen while it's running, and it always sits for a while at creating. Meanwhile it flies through the uniqueness tests. So my question to the stackoverflow community is: Why is my database slowing down as I add more cards? Why is this not a linear function in regards to time per card? I'm sure the answer is simple and I'm just a moron who knows nothing about data storage. And if anyone has any suggestions, how would you optimize this method, and how fast do you think you could get it to create 100,000 cards? (When I plotted out my times on a graph and did a quick curve fit to get my line formula, I calculated how long it would take to create 100,000 cards with my current code and it says 5.5 hours. That maybe completely wrong, I'm not sure. But if it stays on the line I curve fitted, it would be right around there.)

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• How to add image in ListView android

  - by Wawan Den Frastøtende

  i would like to add images on my list view, and i have this code package com.wilis.appmysql; import android.app.ListActivity; import android.content.Intent; import android.os.Bundle; //import android.util.Log; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.Toast; public class menulayanan extends ListActivity { /** Called when the activity is first created. */ public void onCreate(Bundle icicle) { super.onCreate(icicle); // Create an array of Strings, that will be put to our ListActivity String[] menulayanan = new String[] { "Berita Terbaru", "Info Item", "Customer Service", "Help","Exit"}; //Menset nilai array ke dalam list adapater sehingga data pada array akan dimunculkan dalam list this.setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,menulayanan)); } @Override /**method ini akan mengoveride method onListItemClick yang ada pada class List Activity * method ini akan dipanggil apabilai ada salah satu item dari list menu yang dipilih */ protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); // Get the item that was clicked // Menangkap nilai text yang dklik Object o = this.getListAdapter().getItem(position); String pilihan = o.toString(); // Menampilkan hasil pilihan menu dalam bentuk Toast tampilkanPilihan(pilihan); } /** * Tampilkan Activity sesuai dengan menu yang dipilih * */ protected void tampilkanPilihan(String pilihan) { try { //Intent digunakan untuk sebagai pengenal suatu activity Intent i = null; if (pilihan.equals("Berita Terbaru")) { i = new Intent(this, PraBayar.class); } else if (pilihan.equals("Info Item")) { i = new Intent(this, PascaBayar.class); } else if (pilihan.equals("Customer Service")) { i = new Intent(this, CustomerService.class); } else if (pilihan.equals("Help")) { i = new Intent(this, Help.class); } else if (pilihan.equals("Exit")) { finish(); } else { Toast.makeText(this,"Anda Memilih: " + pilihan + " , Actionnya belum dibuat", Toast.LENGTH_LONG).show(); } startActivity(i); } catch (Exception e) { e.printStackTrace(); } } } and i want to add different image per list, so i mean is i want to add a.png to "Berita Terbaru", b.png to "Info Item", c.png "Customer Service" , so how to do it? i was very confused about this, thanks before...

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• Does oneway declaration in Android .aidl guarantee that method will be called in a separate thread?

  - by Dan Menes

  I am designing a framework for a client/server application for Android phones. I am fairly new to both Java and Android (but not new to programming in general, or threaded programming in particular). Sometimes my server and client will be in the same process, and sometimes they will be in different processes, depending on the exact use case. The client and server interfaces look something like the following: IServer.aidl: package com.my.application; interface IServer { /** * Register client callback object */ void registerCallback( in IClient callbackObject ); /** * Do something and report back */ void doSomething( in String what ); . . . } IClient.aidl: package com.my.application; oneway interface IClient { /** * Receive an answer */ void reportBack( in String answer ); . . . } Now here is where it gets interesting. I can foresee use cases where the client calls IServer.doSomething(), which in turn calls IClient.reportBack(), and on the basis of what is reported back, IClient.reportBack() needs to issue another call to IClient.doSomething(). The issue here is that IServer.doSomething() will not, in general, be reentrant. That's OK, as long as IClient.reportBack() is always invoked in a new thread. In that case, I can make sure that the implementation of IServer.doSomething() is always synchronized appropriately so that the call from the new thread blocks until the first call returns. If everything works the way I think it does, then by declaring the IClient interface as oneway, I guarantee this to be the case. At least, I can't think of any way that the call from IServer.doSomething() to IClient.reportBack() can return immediately (what oneway is supposed to ensure), yet IClient.reportBack still be able to reinvoke IServer.doSomething recursively in the same thread. Either a new thread in IServer must be started, or else the old IServer thread can be re-used for the inner call to IServer.doSomething(), but only after the outer call to IServer.doSomething() has returned. So my question is, does everything work the way I think it does? The Android documentation hardly mentions oneway interfaces.

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• XSLT Document function returns empty result on Maven POM

  - by user328618

  Greetings! I want to extract some properties from different Maven POMs in a XSLT via the document function. The script itself works fine but the document function returns an empty result for the POM as long as I have the xmlns="http://maven.apache.org/POM/4.0.0" in the project tag. If I remove it, everything works fine. Any idea how the make this work while leaving the xmlns attribute where it belongs or why this doesn't work with the attribute in place? Here comes the relevant portion of my XSLT: <xsl:template match="abcs"> <xsl:variable name="artifactCoordinate" select="abc"/> <xsl:choose> <xsl:when test="document(concat($artifactCoordinate,'-pom.xml'))"> <abc> <ID><xsl:value-of select="$artifactCoordinate"/></ID> <xsl:copy-of select="document(concat($artifactCoordinate,'-pom.xml'))/project/properties"/> </abc> </xsl:when> <xsl:otherwise> <xsl:message terminate="yes"> Transformation failed: POM "<xsl:value-of select="concat($artifactCoordinate,'-pom.xml')"/>" doesn't exist. </xsl:message> </xsl:otherwise> </xsl:choose> And, for completeness, a POM extract with the "bad" attribute: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <!-- ... --> <properties> <proalpha.version>[5.2a]</proalpha.version> <proalpha.openedge.version>[10.1B]</proalpha.openedge.version> <proalpha.optimierer.version>[1.1]</proalpha.optimierer.version> <proalpha.sonic.version>[7.6.1]</proalpha.sonic.version> </properties> </project>

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• WCF XmlSerializer assembly not speeding up first request

  - by Matt Dearing

  I am generating proxy classes to a clients java webservice wsdls and xsd files with svcutil. The first call made to each service proxy class takes a very long time. I was hoping to speed this up by generating the XmlSerializers assembly myself (based on the article How to: Improve the Startup Time of WCF Client Applications using the XmlSerializer), but when I do the first call to each service still takes the same amount of time. Here are the steps I am following: //generate strong name key file sn -k Blah.snk //generate the proxy class file svcutil blah.wsdl blah2.wsdl blah3.wsdl ... base.xsd blah.xsd ... /UseSerializerForFaults /ser:XmlSerializer /n:*,SomeNamespace /out:Blah.cs //compile the class into an assembly signing it with the strong name key file csc /target:library /keyfile:Blah.snk /out:Blah.dll Blah.cs //generate the XmlSerializer code this will give us Blah.XmlSerializers.dll.cs svcutil /t:xmlSerializer Blah.dll //compile the xmlserializer code into its own dll using the same key to sign it and referencing the original dll csc /target:library /keyfile:Blah.snk /out:Blah.XmlSerializers.dll Blah.XmlSerializers.dll.cs /r:Blah.dll I then create a standard Console application that references both Blah.dll and Blah.XmlSerializers.dll. I will then try something like: //BlahProxy is one of the generated service proxy classes BlahProxy p = new BlahProxy(); //this call takes 30ish seconds p.SomeMethod(); BlahProxy p2 = new BlahProxy(); //this call takes < 1 second p2.SomeMethod(); //BlahProx2y is one of the generated service proxy classes BlahProxy2 p3 = new BlahProxy2(); //this call takes 30ish seconds p3.SomeMethod(); BlahProxy2 p4 = new BlahProxy2(); //this call takes < 1 second p4.SomeMethod(); I know that the problem is not server side because I don't see the request made in Fiddler until around 29 seconds. Subsequent calls to each service take < 1 second, so thats why I was hoping the main slow down was the .net runtime generating the xmlserializer code itself, compiling it and loading the assembly. I figured this would be the reason the first call to each service is slow and the rest are fast. Unfortunatley, me generating the code myself is not speeding anything up. Does anyone see what I am doing wrong?

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• Determine the 'Overtype' mode using Javascript

  - by Snorkpete

  We are creating a web app to replace an old-school green-screen application. In the green-screen app, as the user presses the Insert key to switch between overtype and insert modes, the cursor changes to indicate which input mode the user is currently in. In IE (which is the official browser of the company), overtype mode also works, but there's no visual indication as to whether overtype mode is on or not, until the user starts typing and possibly over-writes existing information unexpectedly. I'd like to put some sort of visual indicator on the screen if in overtype mode. How can you determine if the browser is in 'overtype mode' from Javascript? Is there some property or function i can query to determine if the browser is in overtype mode? Even an IE-specific solution would be helpful, since our corporate policy dictates the browser to use as IE7 (pure torture, btw). (I do know that one solution is to do check for key presses of the Insert key. However, it's a solution that I'd prefer to avoid since that method seems a bit flaky & error-prone because I can't guarantee what mode the user would be in BEFORE he/she hits my page. ) The reasoning behind this question: The functionality of this portion of the green-screen app is such that the user can select from a list of 'preformatted bodies of text'. crude eg. The excess for this policy is: $xxxxxx and max limit is:$xxxxxx Date of policy is: xx/xx/xxxx and expires : xx/xx/xxxx Some other irrelevant text After selecting this 'preformatted text', the user would then use overtype to replace the x's with actual values, without disturbing the alignment of the rest of the text. (To be clear, they can still edit any part of the 'preformatted text' if they so wished. It's just that usually, they just wish to replace specific portions of the text. Keeping the alignment is important since these sections of text can end up on printed documents.) Of course, the same effect can be achieved by just selecting the x's to replace first, but it would be helpful (with respect to easing the transition to the web app) to allow old methods of doing things to continue to work, while still allowing 'web methods' to be used by the more tech-savvy users. Essentially, we're trying to make the initial transition from the green-screen app to the web app be as seemless as possible to minimise the resistance from the long-time green-screeners.

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• Creating meaningful routes in wizard style ASP.NET MVC form

  - by R0MANARMY

  I apologize in advance for a long question, figured better have a bit more information than not enough. I'm working on an application with a fairly complex form (~100 fields on it). In order to make the UI a little more presentable the fields are organized into regions and split across multiple (~10) tabs (not unlike this, but each tab does a submit/redirect to next tab). This large input form can also be in one of 3 views (read only, editable, print friendly). The form represents a large domain object (let's call it Foo). I have a controller for said domain object (FooController). It makes sense to me to have the controller be responsible for all the CRUD related operations. Here are the problems I'm having trouble figuring out. Goals: I'd like to keep to conventions so that Foo/Create creates a new record Foo/Delete deletes a record Foo/Edit/{foo_id} takes you to the first tab of the form ...etc I'd like to be able to not repeat the data access code such that I can have Foo/Edit/{foo_id}/tab1 Foo/View/{foo_id}/tab1 Foo/Print/{foo_id}tab1 ...etc use the same data access code to get the data and just specify which view to use to render it. My current implementation has a massive FooController with Create, Delete, Tab1, Tab2, etc actions. Tab actions are split out into separate files for organization (using partial classes, which may or may not be abuse of partial classes). Problem I'm running into is how to organize my controller(s) and routes to make that happen. I have the default route {controller}/{action}/{id} Which handles goal 1 properly but doesn't quite play nice with goal 2. I tried to address goal 2 by defining extra routes like so: routes.MapRoute( "FooEdit", "Foo/Edit/{id}/{action}", new { controller = "Foo", action = "Tab1", mode = "Edit", id = (string)null } ); routes.MapRoute( "FooView", "Foo/View/{id}/{action}", new { controller = "Foo", action = "Tab1", mode = "View", id = (string)null } ); routes.MapRoute( "FooPrint", "Foo/Print/{id}/{action}", new { controller = "Foo", action = "Tab1", mode = "Print", id = (string)null } ); However defining these extra routes causes the Url.Action to generate routs like Foo/Edit/Create instead of Foo/Create. That leads me to believe I designed something very very wrong, but this is my first attempt an asp.net mvc project and I don't know any better. Any advice with this particular situation would be awesome, but feedback on design in similar projects is welcome.

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• How to produce precisely-timed tone and silence in C#

  - by Bob Denny

  I have a C# project that plays Morse code for RSS feeds. I write it using Managed DirectX, only to discover that Managed DirectX is old and deprecated. The task I have is to play pure sine wave bursts interspersed with silence periods (the code) which are precisely timed as to their duration. I need to be able to call a function which plays a pure tone for so many milliseconds, then Thread.Sleep() then play another, etc. At its fastest, the tones and spaces can be as short as 40ms. It's working quite well in Managed DirectX. To get the precisely timed tone I create 1 sec. of sine wave into a secondary buffer, then to play a tone of a certain duration I seek forward to within x milliseconds of the end of the buffer then play. I've tried System.Media.SoundPlayer. It's a loser because you have to Play(), Sleep(), then Stop() for arbitrary tone lengths. The result is a tone that is too long, variable by CPU load. It takes an indeterminate amount of time to actually stop the tone. I then embarked on a lengthy attempt to use NAudio 1.3. I ended up with a memory resident stream providing the tone data, and again seeking forward leaving the desired length of tone remaining in the stream, then playing. This worked OK on the DirectSoundOut class for a while (see below) but the WaveOut class quickly dies with an internal assert saying that buffers are still on the queue despite PlayerStopped = true. This is odd since I play to the end then put a wait of the same duration between the end of the tone and the start of the next. You'd think that 80ms after starting Play of a 40 ms tone that it wouldn't have buffers on the queue. DirectSoundOut works well for a while, but its problem is that for every tone burst Play() it spins off a separate thread. Eventually (5 min or so) it just stops working. You can see thread after thread after thread exiting in the Output window while running the project in VS2008 IDE. I don't create new objects during playing, I just Seek() the tone stream then call Play() over and over, so I don't think it's a problem with orphaned buffers/whatever piling up till it's choked. I'm out of patience on this one, so I'm asking in the hopes that someone here has faced a similar requirement and can steer me in a direction with a likely solution. Thanks in advance...

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• stdio's remove() not always deleting on time.

  - by Kyte

  For a particular piece of homework, I'm implementing a basic data storage system using sequential files under standard C, which cannot load more than 1 record at a time. So, the basic part is creating a new file where the results of whatever we do with the original records are stored. The previous file's renamed, and a new one under the working name is created. The code's compiled with MinGW 5.1.6 on Windows 7. Problem is, this particular version of the code (I've got nearly-identical versions of this floating around my functions) doesn't always remove the old file, so the rename fails and hence the stored data gets wiped by the fopen(). FILE *archivo, *antiguo; remove("IndiceNecesidades.old"); // This randomly fails to work in time. rename("IndiceNecesidades.dat", "IndiceNecesidades.old"); // So rename() fails. antiguo = fopen("IndiceNecesidades.old", "rb"); // But apparently it still gets deleted, since this turns out null (and I never find the .old in my working folder after the program's done). archivo = fopen("IndiceNecesidades.dat", "wb"); // And here the data gets wiped. Basically, anytime the .old previously exists, there's a chance it's not removed in time for the rename() to take effect successfully. No possible name conflicts both internally and externally. The weird thing's that it's only with this particular file. Identical snippets except with the name changed to Necesidades.dat (which happen in 3 different functions) work perfectly fine. // I'm yet to see this snippet fail. FILE *antiguo, *archivo; remove("Necesidades.old"); rename("Necesidades.dat", "Necesidades.old"); antiguo = fopen("Necesidades.old", "rb"); archivo = fopen("Necesidades.dat", "wb"); Any ideas on why would this happen, and/or how can I ensure the remove() command has taken effect by the time rename() is executed? (I thought of just using a while loop to force call remove() again so long as fopen() returns a non-null pointer, but that sounds like begging for a crash due to overflowing the OS with delete requests or something.)

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• How can I use Web Services Core to send a complex type as a parameter to a SOAP API method

  - by Matthew Brindley

  I don't do much Cocoa programming, so I'm probably missing something obvious, so please excuse the basic question. I have a SOAP method that expects a complex type as a paramater. Here's some WSDL: <s:element name="SaveTestResult"> <s:complexType> <s:sequence> <s:element minOccurs="0" maxOccurs="1" name="result" type="tns:TestItemResponse" /> </s:sequence> </s:complexType> </s:element> Here's the definition of the complex type "TestItemResponse": <s:complexType name="TestItemResponse"> <s:sequence> <s:element minOccurs="1" maxOccurs="1" name="TestItemRequestId" type="s:int" /> <s:element minOccurs="1" maxOccurs="1" name="ExternalId" type="s:int" /> <s:element minOccurs="0" maxOccurs="1" name="ApiId" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="InboxGuid" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="SpamResult" type="tns:SpamResult" /> <s:element minOccurs="0" maxOccurs="1" name="ResultImageSet" type="tns:ResultImageSet" /> <s:element minOccurs="1" maxOccurs="1" name="ExclusiveUseMailAccountId" type="s:int" /> <s:element minOccurs="1" maxOccurs="1" name="State" type="tns:TestItemResponseState" /> <s:element minOccurs="0" maxOccurs="1" name="ErrorShortDescription" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="ErrorFullDescription" type="s:string" /> </s:sequence> </s:complexType> I've been using Web Services Core to call a SOAP API method that requires a simple string param, that works great. That same method returns a complex type which WSC converted into nested NSDictionaries, so no problems there. So I assumed I'd be able to convert my local TestItemResponse class into an NSDictionary and then use that as the complex type param. It almost worked, but unfortunately WSC set the object's type as "Dictionary", instead of "TestItemResponse", and the server complained. <TestItemResponse xsi:type=\"SOAP-ENC:Dictionary\"> <ErrorFullDescription xsi:type=\"xsd:string\">foo</ErrorFullDescription> ... I can't seem to find anything that allows you to override the type WSC assigns to the element in the SOAP XML. I've been using code adapted from here, I'm happy to list it, it's just quite long and this is already the longest SO question I've ever posted.

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• List all possible combinations of k integers between 1...n (n choose k)

  - by Asaf R

  Hi, Out of no particular reason I decided to look for an algorithm that produces all possible choices of k integers between 1...n, where the order amongst the k integer doesn't matter (the n choose k thingy). From the exact same reason, which is no reason at all, I also implemented it in C#. My question is: Do you see any mistake in my algorithm or code? And, more importantly, can you suggest a better algorithm? Please pay more attention to the algorithm than the code itself. It's not the prettiest code I've ever written, although do tell if you see an error. EDIT: Alogirthm explained - We hold k indices. This creates k nested for loops, where loop i's index is indices[i]. It simulates k for loops where indices[i+1] belongs to a loop nested within the loop of indices[i]. indices[i] runs from indices[i - 1] + 1 to n - k + i + 1. CODE: public class AllPossibleCombination { int n, k; int[] indices; List<int[]> combinations = null; public AllPossibleCombination(int n_, int k_) { if (n_ <= 0) { throw new ArgumentException("n_ must be in N+"); } if (k_ <= 0) { throw new ArgumentException("k_ must be in N+"); } if (k_ > n_) { throw new ArgumentException("k_ can be at most n_"); } n = n_; k = k_; indices = new int[k]; indices[0] = 1; } /// <summary> /// Returns all possible k combination of 0..n-1 /// </summary> /// <returns></returns> public List<int[]> GetCombinations() { if (combinations == null) { combinations = new List<int[]>(); Iterate(0); } return combinations; } private void Iterate(int ii) { // // Initialize // if (ii > 0) { indices[ii] = indices[ii - 1] + 1; } for (; indices[ii] <= (n - k + ii + 1); indices[ii]++) { if (ii < k - 1) { Iterate(ii + 1); } else { int[] combination = new int[k]; indices.CopyTo(combination, 0); combinations.Add(combination); } } } } I apologize for the long question, it might be fit for a blog post, but I do want the community's opinion here. Thanks, Asaf

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• Faster Matrix Multiplication in C#

  - by Kyle Lahnakoski

  I have as small c# project that involves matrices. I am processing large amounts of data by splitting it into n-length chunks, treating the chucks as vectors, and multiplying by a Vandermonde** matrix. The problem is, depending on the conditions, the size of the chucks and corresponding Vandermonde** matrix can vary. I have a general solution which is easy to read, but way too slow: public byte[] addBlockRedundancy(byte[] data) { if (data.Length!=numGood) D.error("Expecting data to be just "+numGood+" bytes long"); aMatrix d=aMatrix.newColumnMatrix(this.mod, data); var r=vandermonde.multiplyBy(d); return r.ToByteArray(); }//method This can process about 1/4 megabytes per second on my i5 U470 @ 1.33GHz. I can make this faster by manually inlining the matrix multiplication: int o=0; int d=0; for (d=0; d<data.Length-numGood; d+=numGood) { for (int r=0; r<numGood+numRedundant; r++) { Byte value=0; for (int c=0; c<numGood; c++) { value=mod.Add(value, mod.Multiply(vandermonde.get(r, c), data[d+c])); }//for output[r][o]=value; }//for o++; }//for This can process about 1 meg a second. (Please note the "mod" is performing operations over GF(2^8) modulo my favorite irreducible polynomial.) I know this can get a lot faster: After all, the Vandermonde** matrix is mostly zeros. I should be able to make a routine, or find a routine, that can take my matrix and return a optimized method which will effectively multiply vectors by the given matrix, but faster. Then, when I give this routine a 5x5 Vandermonde matrix (the identity matrix), there is simply no arithmetic to perform, and the original data is just copied. ** Please note: What I use the term "Vandermonde", I actually mean an Identity matrix with some number of rows from the Vandermonde matrix appended (see comments). This matrix is wonderful because of all the zeros, and because if you remove enough rows (of your choosing) to make it square, it is an invertible matrix. And, of course, I would like to use this same routine to convert any one of those inverted matrices into an optimized series of instructions. How can I make this matrix multiplication faster? Thanks! (edited to correct my mistake with Vandermonde matrix)

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• Lightbox image / link URL

  - by GSTAR

  Basically I have a slightly non-standard implementation of FancyBox. By default you have to include a link to the large version of the image so that the Lightbox can display it. However, in my implementation, the image link URLs point to a script rather than directly to the image file. So for example, instead of: <a href="mysite/images/myimage.jpg" rel="gallery"> I have: <a href="mysite/photos/view/abc123" rel="gallery"> The above URL points to a function: public function actionPhotos($view) { $photo=Photo::model()->find('name=:name', array(':name'=>$view)); if(!empty($photo)) { $this->renderPartial('_photo', array('photo'=>$photo, true)); } } The "$this-renderPartial()" bit simply calls a layout file which includes a standard HTML tag to output. Now when the user clicks on a thumbnail, the above function is called and the large image is displayed in the Lightbox. Now if the user right clicks on the thumbnail and selects "open in new tab/window" then the image is displayed in the browser as per normal, i.e. just the image. I want to change this so that it displays the image within a layout. In the above code I can include the following and put it in an IF statement: $this->render('photos', array('photo'=>$photo)); This will call the layout file "photos" which contains the layout to display the image in. I have a specific limitation for this - the image URL must remain the same, i.e. no additional GET variables in the URL. However if we can pass in a GET variable in the background then that is OK. I will most likely need to change my function above so that it calls a different file for this functionality. EDIT: To demonstrate exactly what I am trying to do, check out the following: http://www.starnow.co.uk/KimberleyMarren Go to the photos tab and hover over a thumbnail - note the URL. Click the thumbnail and it will open up in the Lightbox. Next right click on that same thumbnail and select "open in new tab/new window". You will notice that the image is now displayed in a layout. So that same URL is used for displaying the image in the Lightbox and on its own page. The way StarNow have done this is using some crazy long JavaScript functionality, which I'm not too keen on replicating.

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• Custom NSView in NSMenuItem not receiving mouse events

  - by Dennis

  I have an NSMenu popping out of an NSStatusItem using popUpStatusItemMenu. These NSMenuItems show a bunch of different links, and each one is connected with setAction: to the openLink: method of a target. This arrangement has been working fine for a long time. The user chooses a link from the menu and the openLink: method then deals with it. Unfortunately, I recently decided to experiment with using NSMenuItem's setView: method to provide a nicer/slicker interface. Basically, I just stopped setting the title, created the NSMenuItem, and then used setView: to display a custom view. This works perfectly, the menu items look great and my custom view is displayed. However, when the user chooses a menu item and releases the mouse, the action no longer works (i.e., openLink: isn't called). If I just simply comment out the setView: call, then the actions work again (of course, the menu items are blank, but the action is executed properly). My first question, then, is why setting a view breaks the NSMenuItem's action. No problem, I thought, I'll fix it by detecting the mouseUp event in my custom view and calling my action method from there. I added this method to my custom view: - (void)mouseUp:(NSEvent *)theEvent { NSLog(@"in mouseUp"); } No dice! This method is never called. I can set tracking rects and receive mouseEntered: events, though. I put a few tests in my mouseEntered routine, as follows: if ([[self window] ignoresMouseEvents]) { NSLog(@"ignoring mouse events"); } else { NSLog(@"not ignoring mouse events"); } if ([[self window] canBecomeKeyWindow]) { dNSLog((@"canBecomeKeyWindow")); } else { NSLog(@"not canBecomeKeyWindow"); } if ([[self window] isKeyWindow]) { dNSLog((@"isKeyWindow")); } else { NSLog(@"not isKeyWindow"); } And got the following responses: not ignoring mouse events canBecomeKeyWindow not isKeyWindow Is this the problem? "not isKeyWindow"? Presumably this isn't good because Apple's docs say "If the user clicks a view that isn’t in the key window, by default the window is brought forward and made key, but the mouse event is not dispatched." But there must be a way do detect these events. HOW? Adding: [[self window] makeKeyWindow]; has no effect, despite the fact that canBecomeKeyWindow is YES.

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• Is this (Lock-Free) Queue Implementation Thread-Safe?

  - by Hosam Aly

  I am trying to create a lock-free queue implementation in Java, mainly for personal learning. The queue should be a general one, allowing any number of readers and/or writers concurrently. Would you please review it, and suggest any improvements/issues you find? Thank you. import java.util.concurrent.atomic.AtomicReference; public class LockFreeQueue<T> { private static class Node<E> { E value; volatile Node<E> next; Node(E value) { this.value = value; } } private AtomicReference<Node<T>> head, tail; public LockFreeQueue() { // have both head and tail point to a dummy node Node<T> dummyNode = new Node<T>(null); head = new AtomicReference<Node<T>>(dummyNode); tail = new AtomicReference<Node<T>>(dummyNode); } /** * Puts an object at the end of the queue. */ public void putObject(T value) { Node<T> newNode = new Node<T>(value); Node<T> prevTailNode = tail.getAndSet(newNode); prevTailNode.next = newNode; } /** * Gets an object from the beginning of the queue. The object is removed * from the queue. If there are no objects in the queue, returns null. */ public T getObject() { Node<T> headNode, valueNode; // move head node to the next node using atomic semantics // as long as next node is not null do { headNode = head.get(); valueNode = headNode.next; // try until the whole loop executes pseudo-atomically // (i.e. unaffected by modifications done by other threads) } while (valueNode != null && !head.compareAndSet(headNode, valueNode)); T value = (valueNode != null ? valueNode.value : null); // release the value pointed to by head, keeping the head node dummy if (valueNode != null) valueNode.value = null; return value; }

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• php if clause inside foreach not retrieving data correctly

  - by Mike

  Here's my issue: In my controller, I want to grab user input from a form. I then parse the input, and compare it to database values to ensure I'm grabbing the correct input. I simply want to match the user's answers to the question, grab the user ID, the question ID, and then determine if the answer applies to a multiple choice or checkbox question, or something else. I take those values and insert them into the answer table. Ignore the waiver stuff. I'll test that once I get the answers input correctly. // add answers and waiver consent records try { $answerArray = array(); $waiverArray = array(); // retrieve answers, waiver consents, and the question ID's from form object foreach ($formData as $key => $value) { $parts = explode("_", $key); if ($parts[0] == 'question') { array_push($answerArray, $value); } if ($parts[0] == 'waiverTitle') { array_push($waiverArray, $value); } } $questions = new Model_DbTable_Questions(); $questionResults = $questions->getQuestionResults($session->idEvent); foreach ( $questionResults as $qr ) { if ($qr ['questionType'] == 'multipleChoice' || $qr ['questionType'] == 'checkBox') { foreach ( $answerArray as $aa ) { $answerData = $answers->addAnswer ( $lastUserID, $qr ['idQuestion'], null, $aa ); echo count ( $answerData ) . ', ' . $qr ['questionType'] . ', ' . $aa . '<br />'; } } else { foreach ( $answerArray as $aa ) { $answerData = $answers->addAnswer ( $lastUserID, $qr ['idQuestion'], $aa, null ); echo count ( $answerData ) . ', ' . $qr ['questionType'] . ', ' . $aa . '<br />'; } } } } catch (Zend_Db_Statement_Exception $e) { $e->getMessage(); throw $e; } From my test data, I expect to get 2 records that match the multiple choice and checkbox criteria, and 1 record for text in the ELSE clause like this: 3, checkbox, 1 3, multipleChoice, 1 3, text, question_2 What I get is a 3x3 Cartesian product, 3 question elements each with the 3 possible answers like this output from the echo statements: 4, checkBox, 1 4, checkBox, 1 4, checkBox, question_2 4, multipleChoice, 1 4, multipleChoice, 1 4, multipleChoice, question_2 4, text, 1 4, text, 1 4, text, question_2 I've tried placing the IF clause inside the inner foreach, but I get the same results. I've been staring at this problem for way too long and cannot see what I'm doing wrong. Your kind assistance would be greatly appreciated. Please let me know if my request requires more clarification.

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• To use AES with 256 bits in inbuild java 1.4 api.

  - by sahil garg

  I am able to encrypt with AES 128 but with more key length it fails. code using AES 128 is as below. import java.security.*; import javax.crypto.*; import javax.crypto.spec.*; import java.io.*; /** * This program generates a AES key, retrieves its raw bytes, and * then reinstantiates a AES key from the key bytes. * The reinstantiated key is used to initialize a AES cipher for * encryption and decryption. */ public class AES { /** * Turns array of bytes into string * * @param buf Array of bytes to convert to hex string * @return Generated hex string */ public static String asHex (byte buf[]) { StringBuffer strbuf = new StringBuffer(buf.length * 2); int i; for (i = 0; i < buf.length; i++) { if (((int) buf[i] & 0xff) < 0x10) strbuf.append("0"); strbuf.append(Long.toString((int) buf[i] & 0xff, 16)); } return strbuf.toString(); } public static void main(String[] args) throws Exception { String message="This is just an example"; // Get the KeyGenerator KeyGenerator kgen = KeyGenerator.getInstance("AES"); kgen.init(128); // 192 and 256 bits may not be available // Generate the secret key specs. SecretKey skey = kgen.generateKey(); byte[] raw = skey.getEncoded(); SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); // Instantiate the cipher Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec); byte[] encrypted =cipher.doFinal("welcome".getBytes()); System.out.println("encrypted string: " + asHex(encrypted)); cipher.init(Cipher.DECRYPT_MODE, skeySpec); byte[] original = cipher.doFinal(encrypted); String originalString = new String(original); System.out.println("Original string: " + originalString + " " + asHex(original)); } }

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• mysql index optimization for a table with multiple indexes that index some of the same columns

  - by Sean

  I have a table that stores some basic data about visitor sessions on third party web sites. This is its structure: id, site_id, unixtime, unixtime_last, ip_address, uid There are four indexes: id, site_id/unixtime, site_id/ip_address, and site_id/uid There are many different types of ways that we query this table, and all of them are specific to the site_id. The index with unixtime is used to display the list of visitors for a given date or time range. The other two are used to find all visits from an IP address or a "uid" (a unique cookie value created for each visitor), as well as determining if this is a new visitor or a returning visitor. Obviously storing site_id inside 3 indexes is inefficient for both write speed and storage, but I see no way around it, since I need to be able to quickly query this data for a given specific site_id. Any ideas on making this more efficient? I don't really understand B-trees besides some very basic stuff, but it's more efficient to have the left-most column of an index be the one with the least variance - correct? Because I considered having the site_id being the second column of the index for both ip_address and uid but I think that would make the index less efficient since the IP and UID are going to vary more than the site ID will, because we only have about 8000 unique sites per database server, but millions of unique visitors across all ~8000 sites on a daily basis. I've also considered removing site_id from the IP and UID indexes completely, since the chances of the same visitor going to multiple sites that share the same database server are quite small, but in cases where this does happen, I fear it could be quite slow to determine if this is a new visitor to this site_id or not. The query would be something like: select id from sessions where uid = 'value' and site_id = 123 limit 1 ... so if this visitor had visited this site before, it would only need to find one row with this site_id before it stopped. This wouldn't be super fast necessarily, but acceptably fast. But say we have a site that gets 500,000 visitors a day, and a particular visitor loves this site and goes there 10 times a day. Now they happen to hit another site on the same database server for the first time. The above query could take quite a long time to search through all of the potentially thousands of rows for this UID, scattered all over the disk, since it wouldn't be finding one for this site ID. Any insight on making this as efficient as possible would be appreciated :) Update - this is a MyISAM table with MySQL 5.0. My concerns are both with performance as well as storage space. This table is both read and write heavy. If I had to choose between performance and storage, my biggest concern is performance - but both are important. We use memcached heavily in all areas of our service, but that's not an excuse to not care about the database design. I want the database to be as efficient as possible.

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• Synchronized IEnumerator<T>

  - by Dan Bryant

  I'm putting together a custom SynchronizedCollection<T> class so that I can have a synchronized Observable collection for my WPF application. The synchronization is provided via a ReaderWriterLockSlim, which, for the most part, has been easy to apply. The case I'm having trouble with is how to provide thread-safe enumeration of the collection. I've created a custom IEnumerator<T> nested class that looks like this: private class SynchronizedEnumerator : IEnumerator<T> { private SynchronizedCollection<T> _collection; private int _currentIndex; internal SynchronizedEnumerator(SynchronizedCollection<T> collection) { _collection = collection; _collection._lock.EnterReadLock(); _currentIndex = -1; } #region IEnumerator<T> Members public T Current { get; private set;} #endregion #region IDisposable Members public void Dispose() { var collection = _collection; if (collection != null) collection._lock.ExitReadLock(); _collection = null; } #endregion #region IEnumerator Members object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { var collection = _collection; if (collection == null) throw new ObjectDisposedException("SynchronizedEnumerator"); _currentIndex++; if (_currentIndex >= collection.Count) { Current = default(T); return false; } Current = collection[_currentIndex]; return true; } public void Reset() { if (_collection == null) throw new ObjectDisposedException("SynchronizedEnumerator"); _currentIndex = -1; Current = default(T); } #endregion } My concern, however, is that if the Enumerator is not Disposed, the lock will never be released. In most use cases, this is not a problem, as foreach should properly call Dispose. It could be a problem, however, if a consumer retrieves an explicit Enumerator instance. Is my only option to document the class with a caveat implementer reminding the consumer to call Dispose if using the Enumerator explicitly or is there a way to safely release the lock during finalization? I'm thinking not, since the finalizer doesn't even run on the same thread, but I was curious if there other ways to improve this. EDIT After thinking about this a bit and reading the responses (particular thanks to Hans), I've decided this is definitely a bad idea. The biggest issue actually isn't forgetting to Dispose, but rather a leisurely consumer creating deadlock while enumerating. I now only read-lock long enough to get a copy and return the enumerator for the copy.

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• Data access pattern

  - by andlju

  I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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• How to include a PHP generated XML file into flash vars, while ALSO passing through the current php functions into it?

  - by Sam

  Hello Given situation: In webpage.php the flashscript is calling a flash script with a flashvar: the playlist file which is a PHP generated XML file: playlist.php, it does that well so long as there are no extra functions in there. Now, in that XML-format playlistfile there needs to be a special function, besides the usual echo("");, namely the very special echo __(""); function that is already declared in webpage.php which needs to do something with the paragraphs residing within that xml file. However, currently the retrieved file misses the function echo __();and says "no such function declared in that xml-format [playlist.php] file". The php functions that are currently included at the very top of webpage.php somehow do not pass-through-the necessary functions into the playlist file for it to recognise how to handle it, in order for that playlist to get those necessary functions working. Apparently these are not passed through automatically/properly when residing in the flashvars?? Cause the echo __(""); works fine when called within webpage.php or via a normal php include(""); if those functions are in a different php file. But not working from the playlist.php file. Any ideas why/what is going on here? I appreciate your clues for this prob +1. Thanks very much. WEBPAGE.PHP the webpage, has at the top an include with functions: <?php include (functions.php); ?> // function that know what to do with echo __("paragraph") <script language="JavaScript" type="text/javascript"> run( 'play', 'true', 'loop', 'true', 'flashvars', 'xmlFile=/incl/playlist.php', // <<<< !! 'wmode', 'transparent', 'allowScriptAccess','sameDomain', ); </script> <noscript> <object classid="blabla"> <param name="allowScriptAccess" value="sameDomain" /> <param name="movie" value="/movies/movie.swf" /> <param name="flashvars" value="xmlFile=/incl/playlist.php" /> // <<< !! <embed src="/movies/movies.swf" type="application/x-shockwave-flash"/> </object> </noscript> PLAYLIST.PHP The PHP generated XML file which is retrieved into the webpage as flash variable (see above) <?php echo ('<?xml version="1.0" encoding="UTF-8"?>'); echo ('<songs>'); echo ('<song version="1. "') . __("boom blue blow bell bowl") . ('/>'); echo ('<song version="2. "') . __("ball bail beam bike base") . ('/>'); echo ('</songs>'); ?>

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• Need to set cursor position to the end of a contentEditable div, issue with selection and range obje

  - by DavidR

  I'm forgetting about cross-browser compatibility for the moment, I just want this to work. What I'm doing is trying to modify a script (and you probably don't need to know this) located at typegreek.com The basic script is found here. Basically what it does is when you type in characters, it converts the character your are typing into greek characters and prints it onto the screen. What I'm trying to do is to get it to work on contentEditable div's (It only works for Textareas) My issue is with this one function: The user types a key, it get's converted to a greek key, and goes to a function, it gets sorted through some if's, and where it ends up is where I can add div support. Here is what I have so far, myField is the div, myValue is the greek character. //Get selection object... var userSelection if (window.getSelection) {userSelection = window.getSelection();} else if (document.selection) {userSelection = document.selection.createRange();} //Now get the cursor position information... var startPos = userSelection.anchorOffset; var endPos = userSelection.focusOffset; var cursorPos = endPos; //Needed later when reinserting the cursor... var rangeObj = userSelection.getRangeAt(0) var container = rangeObj.startContainer //Now take the content from pos 0 -> cursor, add in myValue, then insert everything after myValue to the end of the line. myField.textContent = myField.textContent.substring(0, startPos) + myValue + myField.textContent.substring(endPos, myField.textContent.length); //Now the issue is, this updates the string, and returns the cursor to the beginning of the div. //so that at the next keypress, the character is inserted into the beginning of the div. //So we need to reinsert the cursor where it was. //Re-evaluate the cursor position, taking into account the added character. var cursorPos = endPos + myValue.length; //Set the caracter position. rangeObj.setStart(container,cursorPos) Now, this works only as long as I don't type more than the size of the original text. Say I had 30 characters in the div before hand. If I type more than that 30, it adds character 31, but places the cursor back at 30. I can type character 32 at pos.31, then character 33 at pos.32, but if I try to put character 34 in, it adds the character, and sets the cursor back at 32. The issue is that the function for adding the new character screws up if cursorPos is greater than what is defined in the range. Any ideas?

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• Java Nimbus LAF with transparent text fields

  - by Software Monkey

  I have an application that uses disabled JTextFields in several places which are intended to be transparent - allowing the background to show through instead of the text field's normal background. When running the new Nimbus LAF these fields are opaque (despite setting setOpaque(false)), and my UI is broken. It's as if the LAF is ignoring the opaque property. Setting a background color explicitly is both difficult in several places, and less than optimal due to background images actually doesn't work - it still paints it's LAF default background over the top, leaving a border-like appearance (the splash screen below has the background explicitly set to match the image). Any ideas on how I can get Nimbus to not paint the background for a JTextField? Note: I need a JTextField, rather than a JLabel, because I need the thread-safe setText(), and wrapping capability. Note: My fallback position is to continue using the system LAF, but Nimbus does look substantially better. See example images below. Conclusions The surprise at this behavior is due to a misinterpretation of what setOpaque() is meant to do - from the Nimbus bug report: This is a problem the the orginal design of Swing and how it has been confusing for years. The issue is setOpaque(false) has had a side effect in exiting LAFs which is that of hiding the background which is not really what it is ment for. It is ment to say that the component my have transparent parts and swing should paint the parent component behind it. It's unfortunate that the Nimbus components also appear not to honor setBackground(null) which would otherwise be the recommended way to stop the background painting. Setting a fully transparent background seems unintuitive to me. In my opinion, setOpaque()/isOpaque() is a faulty public API choice which should have been only: public boolean isFullyOpaque(); I say this, because isOpaque()==true is a contract with Swing that the component subclass will take responsibility for painting it's entire background - which means the parent can skip painting that region if it wants (which is an important performance enhancement). Something external cannot directly change this contract (legitimately), whose fulfillment may be coded into the component. So the opacity of the component should not have been settable using setOpaque(). Instead something like setBackground(null) should cause many components to "no long have a background" and therefore become not fully opaque. By way of example, in an ideal world most components should have an isOpaque() that looks like this: public boolean isOpaque() { return (background!=null); }

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• launching mapview from main activity (button)

  - by arc

  Hi all. Going round in circles here i think. I have an activity called Locate; public class Locate extends Activity { public static String lat; public static String lon; public static String number; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.locate); final Button buttonMaps = (Button) findViewById(R.id.ButtonMaps); buttonMaps.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { Toast.makeText(getBaseContext(), "Button Pressed", Toast.LENGTH_SHORT).show(); try { Intent i = new Intent(getBaseContext(), displayMap.class); i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); startActivity(i); } catch (ActivityNotFoundException e) { Toast.makeText(getBaseContext(), "Activity Not Found", Toast.LENGTH_SHORT).show(); } }}); // Toast.makeText(getBaseContext(), "lat: " + lat + " long: " + lon + " from: " + testname, Toast.LENGTH_LONG).show(); } If I make the displayMap class into a normal Activity, and just have display a toast message confirming it has loaded - then it works fine. If i do this though; public class displayMap extends MapActivity { /** Called when the activity is first created. */ public void onCreate() { setContentView(R.layout.displaymap); Toast.makeText(getBaseContext(), "Display Map", Toast.LENGTH_SHORT).show(); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } Then as soon as I click the Button, I get a force close. I have the correct 'uses-library' tag in my manifest; <application android:icon="@drawable/icon" android:label="@string/app_name"> <uses-library android:name="com.google.android.maps" /> I don't get what it just force closes everytime i try and load it. If I make this my onClick handler then it will fire up a working googlemaps/default mapview public void onClick(View v) { Toast.makeText(getBaseContext(), "Button Pressed", Toast.LENGTH_SHORT).show(); Uri uri=Uri.parse("geo:"+Locate.lat+","+Locate.lon); StartActivity(new Intent(Intent.ACTION_VIEW, uri)); } But that is not what I am trying to do, I want my own - so that I can add overlays etc to it. But it does prove that the permission are set correctly and that the lib is there. The logcat error when the app FCs is a Unexpected DEX error. Can anyone point in the right direction here?

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