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Articles indexed Wednesday May 19 2010

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  • Natural problems to solve using closures

    - by m.u.sheikh
    I have read quite a few articles on closures, and, embarassingly enough, I still don't understand this concept! Articles explain how to create a closure with a few examples, but I don't see any point in paying much attention to them, as they largely look contrived examples. I am not saying all of them are contrived, just that the ones I found looked contrived, and I dint see how even after understanding them, I will be able to use them. So in order to understand closures, I am looking at a few real problems, that can be solved very naturally using closures. For instance, a natural way to explain recursion to a person could be to explain the computation of n!. It is very natural to understand a problem like computing the factorial of a number using recursion. Similarly, it is almost a no-brainer to find an element in an unsorted array by reading each element, and comparing with the number in question. Also, at a different level, doing Object-oriented programming also makes sense. So I am trying to find a number of problems that could be solved with or without closures, but using closures makes thinking about them and solving them easier. Also, there are two types to closures, where each call to a closure can create a copy of the environment variables, or reference the same variables. So what sort of problems can be solved more naturally in which of the closure implementations?

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  • Diffrernce between BackgroundWorker.ReportProgress() and Control.Invoke()

    - by ohadsc
    What is the difference between options 1 and 2 in the following? private void BGW_DoWork(object sender, DoWorkEventArgs e) { for (int i=1; i<=100; i++) { string txt = i.ToString(); if (Test_Check.Checked) //OPTION 1 Test_BackgroundWorker.ReportProgress(i, txt); else //OPTION 2 this.Invoke((Action<int, string>)UpdateGUI, new object[] {i, txt}); } } private void BGW_ProgressChanged(object sender, ProgressChangedEventArgs e) { UpdateGUI(e.ProgressPercentage, (string)e.UserState); } private void UpdateGUI(int percent, string txt) { Test_ProgressBar.Value = percent; Test_RichTextBox.AppendText(txt + Environment.NewLine); } Looking at reflector, the Control.Invoke() appears to use: this.FindMarshalingControl().MarshaledInvoke(this, method, args, 1); whereas BackgroundWorker.Invoke() appears to use: this.asyncOperation.Post(this.progressReporter, args); (I'm just guessing these are the relevant function calls.) If I understand correctly, BGW Posts to the WinForms window its progress report request, whereas Control.Invoke uses a CLR mechanism to invoke on the right thread. Am I close? And if so, what are the repercussions of using either ? Thanks

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  • Why is the 'var' keyword bad? Or am I just old school?

    - by WaggingSiberian
    Recently I overheard junior developer ask "why do you use 'var' so much?". The mid-level developer responded "I use VAR all the time. I love it! I don't have to figure out the type." I didn't have the time or energy to get into a religious war and hey, I'm still the new guy here :-) I understand var has its place. LINQ comes to mind. But I have also always been told the use of var represents lazy programming and I should just use the correct type to begin with. If it's an int, define it as an int, not a var. When reviewing code, seeing the type makes it easier to follow. My opinion is, it's just lazy but there are exception. Var also reminds me of the VB/VBA variant type. It also had its place. I recall (from many years ago) its usage being less-than-desirable type and it was rather resource hungry. Am I just being stuck in my ways? Should we start using var all the time as my co-worker does?

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  • replacing toString using Groovy metaprogramming

    - by Don
    In the following Groovy snippet, I attempt to replace both the hashCode and toString methods String.metaClass.toString = {-> "override" } String.metaClass.hashCode = {-> 22 } But when I test it out, only the replacement of hashCode works String s = "foo" println s.hashCode() // prints 22 println s.toString() // prints "foo" Is toString somehow a special case (possibly for security reasons)?

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  • How to get application to use specific version of .NET?

    - by HN
    Hi, I am using pnunit to run nunit tests on remote machines, the pnunit agent loads the test and runs it in Windows 2008 but the test fails to load in Windows 2003, the agent error is INFO PNUnit.Agent.PNUnitAgent - Registering channel on port 9080 INFO PNUnit.Agent.PNUnitAgent - RunTest called for Test MyTest, AssemblyName test.dll, TestToRun test.Program.myDeployTest INFO PNUnit.Agent.PNUnitTestRunner - Spawning a new thread INFO PNUnit.Agent.PNUnitTestRunner - Thread entered for Test MyTest:test.Program.myDeployTest Assembly test.dll Unhandled Exception: System.BadImageFormatException: The format of the file 'test ' is invalid. File name: "test" Server stack trace: at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, B oolean isStringized, Evidence assemblySecurity, Boolean throwOnFileNotFound, Ass embly locationHint, StackCrawlMark& stackMark) On running procmon and monitoring the agent process i could see that the agent executable was using .NET 1.1 assemblies on Windows 2003 and .NET 2.0 on Windows 2008 which could be an explanation for this behavior. How do I get the agent to use .NET 2.0 on Windows 2003?

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  • CouchDB on Windows?

    - by epitka
    I started exploring CouchDB and I am interested in following: Is there or will there be a Windows install? If there is, is there a shared hosting provider that offers CouchDB? Not knowing much about it, can it be somehow embedded in my application or bin deployed (don't laugh).

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  • Spring Test / JUnit problem - unable to load application context

    - by HDave
    I am using Spring for the first time and must be doing something wrong. I have a project with several Bean implementations and now I am trying to create a test class with Spring Test and JUnit. I am trying to use Spring Test to inject a customized bean into the test class. Here is my test-applicationContext.xml: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="............."> <bean id="MyUuidFactory" class="com.myapp.UuidFactory" scope="singleton" > <property name="typeIdentifier" value="CLS" /> </bean> <bean id="ThingyImplTest" class="com.myapp.ThingyImplTest" scope="singleton"> <property name="uuidFactory"> <idref local="MyUuidFactory" /> </property> </bean> </beans> The injection of MyUuidFactory instance goes along with the following code from within the test class: private UuidFactory uuidFactory; public void setUuidFactory(UuidFactory uuidFactory) { this.uuidFactory = uuidFactory; } However, when I go to run the test (in Eclipse or command line) I get the following error (stack trace omitted for brevity): Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'MyImplTest' defined in class path resource [test-applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.lang.String' to required type 'com.myapp.UuidFactory' for property 'uuidFactory'; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.myapp.UuidFactory] for property 'uuidFactory': no matching editors or conversion strategy found Funny thing is, the Eclipse/Spring XML editor shows errors of I misspell any of the types or idrefs. If I leave the bean in, but comment out the dependency injection, everything work until I get a NullPointerException while running the test...which makes sense.

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  • Who deletes the copied instance in + operator ? (c++)

    - by Dima
    Hello, I searched how to implement + operator properly all over the internet and all the results i found do the following steps : const MyClass MyClass::operator+(const MyClass &other) const { MyClass result = *this; // Make a copy of myself. Same as MyClass result(*this); result += other; // Use += to add other to the copy. return result; // All done! } I have few questions about this "process" : Isn't that stupid to implement + operator this way, it calls the assignment operator(which copies the class) in the first line and then the copy constructor in the return (which also copies the class , due to the fact that the return is by value, so it destroys the first copy and creates a new one.. which is frankly not really smart ... ) When i write a=b+c, the b+c part creates a new copy of the class, then the 'a=' part copies the copy to himself. who deletes the copy that b+c created ? Is there a better way to implement + operator without coping the class twice, and also without any memory issues ? thanks in advance

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  • mysqli insert problem

    - by Simon
    Hello i have this error: Warning: mysqli_stmt::bind_param() [mysqli-stmt.bind-param]: Number of elements in type definition string doesn't match number of bind variables in E:\wamp\www\classes\UserLogin.php on line 31 and i dont know what it is :/ here is my code function createUser($username, $password) { $mysql = connect(); if($stmt = $mysql->prepare('INSERT INTO users (username, password, alder, hood, fornavn, efternavn, city, ip, level, email) VALUES (?,?,?,?,?,?,?,?,?,?)')) { $stmt->bind_param($username,$password, $alder, $hood, $fornavn, $efternavn, $city, $ip, $level, $email); $stmt->execute(); $stmt->close(); } else { echo 'error: ' . $mysql->error; } then my user create the user they only need to type username and password, and later they can edit the profile and edit, email,alder,hood and like that :). Thanks for helping me

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  • Drupal 6 sign-up booking, reservation system with payments

    - by Lukasz
    Hi Guys. I have tried to find out the working solution for implementing simple events booking system in Drupal 6 (limited places, payment, signing up/buying few places for firends). System does not have to be big but easy to customize events to reserve/book places for. I was surprised of not finding much complete solutions. Most of the time I was directed to use modules like: Date, Calendar, Singup, Singup Ubercraft integration, Ubercraft. Does anybody of you has tested it? Is it working and customizable or you would suggest other alternatives on the subject? Wiil appreciate any recomendations.

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  • Delphi dbExpress and Interbase: UTF8 migration steps and risks?

    - by mjustin
    Currently, our database uses Win1252 as the only character encoding. We will have to support Unicode in the database tables soon, which means we have to perform this migration for four databases and around 80 Delphi applications which run in-house in a 24/7 environment. Are there recommendations for database migrations to UTF-8 (or UNICODE_FSS) for Delphi applications? Some questions listed below. Many thanks in advance for your answers! are there tools which help with the migration of the existing databases (sizes between 250 MB and 2 GB, no Blob fields), by dumping the data, recreating the database with UNICODE_FSS or UTF-8, and loading the data back? are there known problems with Delphi 2009, dbExpress and Interbase 7.5 related to Unicode character sets? would you recommend to upgrade the databases to Interbase 2009 first? (This upgrade is planned but does not have a high priority) can we simply migrate the database and Delphi will handle the Unicode character sets automatically, or will we have to change all character field types in every Datamodule (dfm and source code) too? which strategy would you recommend to work on the migration in parallel with the normal development and maintenance of the existing application? The application runs in-house so development and database administration is done internally.

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  • weekly Automatic running sql server script

    - by AmRoSH
    I have sql server script and i want to automatic run it on the database every week. any help. i tried sql server agent job but i have alot of data bases on my server and i should make step to every database and it will run in the same day and same time.

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  • div style working in Firefox but not IE8

    - by Nathan Spiwak
    I am creating a banner that resizes to fit the window (I got the code of a blog post) and it works fine in Firefox, but it doesn't display at all in IE8. Please help!! <html> <body> <div style="position:relative; width:100%; height:100%; margin:0px; padding:0px; left:0px;right:0px;z-index:1”><img src="https://na6.salesforce.com/servlet/servlet.ImageServer?id=01580000000pT8r&oid=00D80000000aYeL&lastMod=1273785188000" width="100%"></div> <div style="z-index:2; position:relative; margin:0px; padding:0px;"> </div> </body> </html>

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  • difficulty based time estimation software

    - by Frankie
    Some months ago I found a project-management / time-estimation software that would ask you to sort out your tasks in terms of difficulty (1, 2 or 3) and would then estimate the time you would take to deploy. The system would auto-adapt as you were working. I've forgot the software name. For the past days I've been digging emails and searching Google with no results. Can anyone pin the software name by my description? Its not http://www.fogcreek.com (though I've found it to be a great piece of software. Thank you in advance.

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  • gwt typeahead missing

    - by arinte
    I have a GWT app with a bunch of textboxes. In firefox I would expect that when I type a word in a textbox that I have already typed in and submitted, that firefox would offer to autocomplete that text. But for this GWT app it is not happening. Also in IE it seems that none of my css stuff is loaded. And when I IE developer tools on my GWT page, it can focus in on any of the textboxes it just focuses on the encompassing DIV around all the textboxes.

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  • Draw to an Image

    - by nXqd
    I'm new to GDI+ and I don't know how to draw to an Image. I've a matrix ( game map ) and tiles, Can I create an Image or a Bitmap, then I draw everything on it, so I can work with it likes an Image I load from resources. Thanks so much :)

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  • MvcExtensions - PerRequestTask

    - by kazimanzurrashid
    In the previous post, we have seen the BootstrapperTask which executes when the application starts and ends, similarly there are times when we need to execute some custom logic when a request starts and ends. Usually, for this kind of scenario we create HttpModule and hook the begin and end request events. There is nothing wrong with this approach, except HttpModules are not at all IoC containers friendly, also defining the HttpModule execution order is bit cumbersome, you either have to modify the machine.config or clear the HttpModules and add it again in web.config. Instead, you can use the PerRequestTask which is very much container friendly as well as supports execution orders. Lets few examples where it can be used. Remove www Subdomain Lets say we want to remove the www subdomain, so that if anybody types http://www.mydomain.com it will automatically redirects to http://mydomain.com. public class RemoveWwwSubdomain : PerRequestTask { public RemoveWww() { Order = DefaultOrder - 1; } protected override TaskContinuation ExecuteCore(PerRequestExecutionContext executionContext) { const string Prefix = "http://www."; Check.Argument.IsNotNull(executionContext, "executionContext"); HttpContextBase httpContext = executionContext.HttpContext; string url = httpContext.Request.Url.ToString(); bool startsWith3W = url.StartsWith(Prefix, StringComparison.OrdinalIgnoreCase); bool shouldContinue = true; if (startsWith3W) { string newUrl = "http://" + url.Substring(Prefix.Length); HttpResponseBase response = httpContext.Response; response.StatusCode = (int)HttpStatusCode.MovedPermanently; response.Status = "301 Moved Permanently"; response.RedirectLocation = newUrl; response.SuppressContent = true; shouldContinue = false; } return shouldContinue ? TaskContinuation.Continue : TaskContinuation.Break; } } As you can see, first, we are setting the order so that we do not have to execute the remaining tasks of the chain when we are redirecting, next in the ExecuteCore, we checking the whether www is present, if present we are sending a permanently moved http status code and breaking the task execution chain otherwise we are continuing with the chain. Blocking IP Address Lets take another scenario, your application is hosted in a shared hosting environment where you do not have the permission to change the IIS setting and you want to block certain IP addresses from visiting your application. Lets say, you maintain a list of IP address in database/xml files which you want to block, you have a IBannedIPAddressRepository service which is used to match banned IP Address. public class BlockRestrictedIPAddress : PerRequestTask { protected override TaskContinuation ExecuteCore(PerRequestExecutionContext executionContext) { bool shouldContinue = true; HttpContextBase httpContext = executionContext.HttpContext; if (!httpContext.Request.IsLocal) { string ipAddress = httpContext.Request.UserHostAddress; HttpResponseBase httpResponse = httpContext.Response; if (executionContext.ServiceLocator.GetInstance<IBannedIPAddressRepository>().IsMatching(ipAddress)) { httpResponse.StatusCode = (int)HttpStatusCode.Forbidden; httpResponse.StatusDescription = "IPAddress blocked."; shouldContinue = false; } } return shouldContinue ? TaskContinuation.Continue : TaskContinuation.Break; } } Managing Database Session Now, let see how it can be used to manage NHibernate session, assuming that ISessionFactory of NHibernate is already registered in our container. public class ManageNHibernateSession : PerRequestTask { private ISession session; protected override TaskContinuation ExecuteCore(PerRequestExecutionContext executionContext) { ISessionFactory factory = executionContext.ServiceLocator.GetInstance<ISessionFactory>(); session = factory.OpenSession(); return TaskContinuation.Continue; } protected override void DisposeCore() { session.Close(); session.Dispose(); } } As you can see PerRequestTask can be used to execute small and precise tasks in the begin/end request, certainly if you want to execute other than begin/end request there is no other alternate of HttpModule. That’s it for today, in the next post, we will discuss about the Action Filters, so stay tuned.

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  • ASP.NET hosting: better, faster, cheaper

    After seven years with webhost4life, it was time to move on. Especially because of all the troubles with webhost4life due to their internal migration to a new hosting environment (the company has been bought out).I've just moved all my websites elsewhere. I'm now using Arvixe and OrcsWeb.I use OrcsWeb for metaSapiens.com. OrcsWeb kindly offers me free ASP.NET hosting because I'm a Microsoft MVP. I'd like to publicly thank OrcsWeb for this, and I invite you to have a look at what they have to offer.I...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Using HTML entities in XML Literals (Avner Aharoni)

    One of the common use-cases of XML literals is creating HTML. However, HTML entities cannot be used in XML literals since LINQ to XML directly supports only the Data type definitions (DTD) defined in the XML 1.0 spec. You can read more about it here. The workaround is to use the Unicode representation of the entity, although its not as readable as the HTML entities, the output is the same. Here are two examples of HTML entities from the XHTML spec :   Entity...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Azure Blob and Entity Table Integration, extending the Thumbnail sample

    This article describes the concepts for doing CRUD (Create, Read, Update, Delete) operations on Windows Azure Tables and how table data can interact with the Blobs....Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • TCP Zero Window with no corresponding Window Update

    - by Gandalf
    I am trying to debug a network issue and am using Wireshark and tcpdump to grab packets from my server. I have one client application that is grabbing all my available connections and then holding them, trying to send A LOT of data and essentially causing an unintentional DOS attack. While debugging I notice that I see my server sending "Window Closed" and "Zero Window" TCP packets - but never sending any "Window Update" packets. I am guessing this is why the client never lets go of the connections (it still has more data to send and is waiting). Has anyone ever seen this type of behavior before? Let's not get into the reasons why I haven't set up an iptables rule to limit concurrent connections (yeah I know). I also recently changed the MTU from 1500 to 9000 - could this have such a negative effect? (Linux) Thanks.

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