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• Creating WPF components in background thread

  - by mizipzor

  Im working on a reporting system, a series of DocumentPage are to be created through a DocumentPaginator. These documents include a number of WPF components that are to be instantiated so the paginator includes the correct things when later sent to the XpsDocumentWriter (which in turn is sent to the actual printer). My problem now is that the DocumentPage instances take quite a while to create (enough for Windows to mark the application as frozen) so I tried to create them in a background thread, which is problematic since WPF expects the attributes on them to be set from the GUI thread. I would also like to have a progress bar showing up, indicating how many pages have been created so far. Thus, it looks like Im trying to get two things to happen in parallell on the GUI. The problem is hard to explain and Im really not sure how to tackle it. In short: Create a series of DocumentPage's. These include WPF components These are to be created on a background thread, or use some other trick so the application isnt frozen. After each page is created, a WPF ProgressBar should be updated. If there is no decent way to do this, alternate solutions and approaches are more than welcome.

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• how do use Ninject with class libraries I am developing?

  - by Greg

  Hi, If I am working on a class library how do I make use of Ninject here? Ie from the internal class library point of view and also from the client code? For example: should the class library have it's own IOC set up, or should it always assume the client code will supply? if no (ie it's upto the client to have the IOC in place) then where is the mapping data stored here'. Is this mapping of the class library's functionality to be places in the client? have a reusable library that is available, that uses interfaces with classes that use the getInstance concept to create concrete classes for you to use, then in this case would that make sense on the client side to use the IOC container to create instances of these classes? Or is that really applying a double layer of abstraction? Q2 Or in the cases where I'm building the reusable library myself and want the client to use an IOC container, then in my reusable library would I then dispense with any overhead of having factories or "getInstance" methods to instantiate the classes in the client? (i.e. as the IOC container would do this no?)

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• BASH echo write mysql input

  - by jmituzas

  Have a bash menu where variables write to file for mysql input. heres what I have: echo "CREATE DATABASE '$mysqldbn'; #GRANT ALL PRIVILEGES ON *.* TO '$mysqlu'@'$myhost' IDENTIFIED BY '$mysqlup' WITH GRANT OPTION; GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES ON '$mysqldbn'.* TO '$mysqlu'@'$myhost' IDENTIFIED BY '$mysqlup'; GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES ON '$mysqldbn'.* TO '$mysqlu'@'$myip' IDENTIFIED BY '$mysqlup'; GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES ON '$mysqldbn'.* TO '$mysqlu'@'localhost' IDENTIFIED BY '$mysqlup'; GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, CREATE TEMPORARY TABLES< LOCK TABLES on '$mysqldbn'.* TO '$mysqlu'@'$rip' IDENTIFIED BY '$mysqlup';" > nmysql.db mysql -u root -p$mypass < nmysql.db problem is to get variables to show I had to put them in single quotes, the single quotes show up as I want for instances like '$mysqlu'@'localhost'. But how can I remove the quotes and still get to use the variable in the instance like, CREATE DATABASE '$mysqldbn' ? Double quotes wont work either, I am at a loss. Thanks in advance, Joe

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• iPhone: Does it ever make sense for an object to retain its delegate?

  - by randombits

  According to the rules of memory management in a non garbage collected world, one is not supposed to retain a the calling object in a delegate. Scenario goes like this: I have a class that inherits from UITableViewController and contains a search bar. I run expensive search operations in a secondary thread. This is all done with an NSOperationQueue and subclasses NSOperation instances. I pass the controller as a delegate that adheres to a callback protocol into the NSOperation. There are edge cases when the application crashes because once an item is selected from the UITableViewController, I dismiss it and thus its retain count goes to 0 and dealloc gets invoked on it. The delegate didn't get to send its message in time as the results are being passed at about the same time the dealloc happens. Should I design this differently? Should I call retain on my controller from the delegate to ensure it exists until the NSOperation itself is dealloc'd? Will this cause a memory leak? Right now if I put a retain on the controller, the crashes goes away. I don't want to leak memory though and need to understand if there are cases where retaining the delegate makes sense. Just to recap. UITableViewController creates an NSOperationQueue and NSOperation that gets embedded into the queue. The UITableViewController passes itself as a delegate to NSOperation. NSOperation calls a method on UITableViewController when it's ready. If I retain the UITableViewController, I guarantee it's there, but I'm not sure if I'm leaking memory. If I only use an assign property, edge cases occur where the UITableViewController gets dealloc'd and objc_msgSend() gets called on an object that doesn't exist in memory and a crash is imminent.

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• Debugged Program Window Won't Close

  - by Marc Bernier

  Hi, I'm using VS 2008 on a 64-bit XP machine. I'm debugging a 32-bit C++ DLL via a console program. The DLL and EXE projects are contained in the same SLN so that I can modify the DLL as I test. What happens is that every once in a while I kill the program with Debug | Stop Debugging (Shift-F5). VS stops the program, but the console window stays open! If I'm sitting at a breakpoint and hit Shift-F5, it will terminate properly, but if the program is running full-tilt when I stop it, I often see this instead. The big problem is that I can't close these zombie windows. Using End Task in Task Manager does nothing (no message, no nothing). When I shut down the machine, it is unable to due to the orphans and I have to resort to actually turning off the power. I think this is connected to having the DLL and EXE project in the same SLN, as for months I worked on this project in 2 VS instances, one for the DLL and the other for the EXE. I would continually jump back and forth between the windows as I worked. This problem never happened until I put the two projects into a single SLN. The single SLN works a lot better, but this anomaly is very irritating. Any ideas anyone? UPDATE After a bit of searching (here), I found that it appears to have to do with one of the updates from last Tuesday (KB977165 or KB978037). Thank you Microsoft for your excellent pre-release testing.

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• Handling Types Defined in Plug-ins That Are No Longer Available

  - by Chris

  I am developing a .NET framework application that allows users to maintain and save "projects". A project can consist of components whose types are defined in the assemblies of the framework itself and/or in third-party assemblies that will be made available to the framework via a yet-to-be-built plug-in architecture. When a project is saved, it is simply binary-serialised to file. Projects are portable, so multiple users can load the same project into their own instances of the framework (just as different users may open the same MSWord document in their own local copies of MSWord). What's more, the plug-ins available to one user's framework might not be available to that of another. I need some way of ensuring that when a user attempts to open (i.e. deserialise) a project that includes a type whose defining assembly cannot be found (either because of a framework version incompatibility or the absence of a plug-in), the project still opens but the offending type is somehow substituted or omitted. Trouble is, the research I've done to date does not even hint at a suitable approach. Any ideas would be much appreciated, thanks.

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• Finding ALL positions of a substring in a large string in C#

  - by Tommy

  Alright, so what i have, is a large string i need to parse, and what i need to happen, is find all the instances of extract"(me,i-have lots. of]punctuation, and store them to a list. So say this piece of string was in the beginning and middle of the larger string, both of them would be found, and their index's would be added to the List. and the List would contain 0 and the other index whatever it would be. Ive been playing around, and the string.IndexOf does almost what i'm looking for, and ive written some code. But i cant seem to get it to work: List<int> inst = new List<int>(); int index = 0; while (index < source.LastIndexOf("extract\"(me,i-have lots. of]punctuation", 0) + 39) { int src = source.IndexOf("extract\"(me,i-have lots. of]punctuation", index); inst.Add(src); index = src + 40; } inst = The list source = The large string Any better ideas?

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• Resque: Slow worker startup and Forking

  - by David John

  I'm currently moving my application from a Linode setup to EC2. Redis is currently installed on a remote instance with various worker instances interacting with the queue. Thats all going fantastic. My problem is with the amount of time it takes for a worker to be 'instantiated' and slow forking. Starting a worker will usually take between 30 seconds and a minute(from god.rb starting the worker rake task and the worker actively starting work on the queue). I could live with that, but I've not experienced such a wait time on my current Linode production box so I believe its one of my symptoms to a bigger problem. Next issue is that jobs that took a second or less in my previous environment now seem to take about 5 to 10 times longer.. I'm assuming this must be some sort of issue with my Ubuntu install on EC2? One notable difference is that I'm running REE 1.8.7-2010.01 in my new setup, and REE 1.8.6 on the old Linode boxes. Anyone else experienced these issues?

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• How do I get my Flash CS4 buttons to direct the user to another URL?

  - by goldenfeelings

  My apologies if this has been fully addressed before, but I've read through several other threads and still can't seem to get my file to work. My actionscript code is at the bottom of this message. I created it using instructions from the Adobe website: http://help.adobe.com/en_US/ActionScript/3.0_ProgrammingAS3/WS5b3ccc516d4fbf351e63e3d118a9b90204-7fd7.html I believe I have all of my objects set to the correct type of symbol (button) and all of my instances are named appropriately (see screenshot here: www.footprintsfamilyphoto.com/wp-content/themes/Footprints/images/flash_buttonissue.jpg) Action Script here. Let me know if you have suggestions! (Note: I am very new to Flash): stop (); function families(event:MouseEvent):void { var targetURL:URLRequest = new URLRequest("http://www.footprintsfamilyphoto.com/portfolio/families"); navigateToURL(targetURL); } bc_btn1.addEventListener(MouseEvent.CLICK, families); bc_btn2.addEventListener(MouseEvent.CLICK, families); function families(event:MouseEvent):void { var targetURL:URLRequest = new URLRequest("http://www.footprintsfamilyphoto.com/portfolio/families"); navigateToURL(targetURL); } f_btn1.addEventListener(MouseEvent.CLICK, families); f_btn2.addEventListener(MouseEvent.CLICK, families); function families(event:MouseEvent):void { var targetURL:URLRequest = new URLRequest("http://www.footprintsfamilyphoto.com/portfolio/families"); navigateToURL(targetURL); } cw_btn1.addEventListener(MouseEvent.CLICK, families); cw_btn2.addEventListener(MouseEvent.CLICK, families);

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• Is there any way to provide custom factory for .Net Framework creation Entities from EF4 ?

  - by ILICH

  There are a lot of posts about how cool POCO objects are and how Entity Framework 4 supports them. I decided to try it out with domain driven development oriented architecture and finished with domain entities that has dependencies from services. So far so good. Imagine my Products are POCO objects. When i query for objects like this: NorthwindContext db = new NorthwindContext(); var products = db.Products.ToList(); EF creates instances of products for me. Now I want to inject dependencies in my POCO objects (products) The only way I see is make some method within NorthwindContext that makes something like pseudo-code below: public List<Product> GetProducts(){ var products = database.Products.ToList(); container.BuildUp(products); //inject dependencies return products; } But what if i want to make my repository to be more flexible like this: public ObjectSet<Product> GetProducts() { ... } So, I really need a factory to make it more lazy and linq friendly. Please help !

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• Right way to return proxy model instance from a base model instance in Django ?

  - by sotangochips

  Say I have models: class Animal(models.Model): type = models.CharField(max_length=255) class Dog(Animal): def make_sound(self): print "Woof!" class Meta: proxy = True class Cat(Animal): def make_sound(self): print "Meow!" class Meta: proxy = True Let's say I want to do: animals = Animal.objects.all() for animal in animals: animal.make_sound() I want to get back a series of Woofs and Meows. Clearly, I could just define a make_sound in the original model that forks based on animal_type, but then every time I add a new animal type (imagine they're in different apps), I'd have to go in and edit that make_sound function. I'd rather just define proxy models and have them define the behavior themselves. From what I can tell, there's no way of returning mixed Cat or Dog instances, but I figured maybe I could define a "get_proxy_model" method on the main class that returns a cat or a dog model. Surely you could do this, and pass something like the primary key and then just do Cat.objects.get(pk = passed_in_primary_key). But that'd mean doing an extra query for data you already have which seems redundant. Is there any way to turn an animal into a cat or a dog instance in an efficient way? What's the right way to do what I want to achieve?

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• Full Text Search like Google

  - by Eduardo

  I would like to implement full-text-search in my off-line (android) application to search the user generated list of notes. I would like it to behave just like Google (since most people are already used to querying to Google) My initial requirements are: Fast: like Google or as fast as possible, having 100000 documents with 200 hundred words each. Searching for two words should only return documents that contain both words (not just one word) (unless the OR operator is used) Case insensitive (aka: normalization): If I have the word 'Hello' and I search for 'hello' it should match. Diacritical mark insensitive: If I have the word 'así' a search for 'asi' should match. In Spanish, many people, incorrectly, either do not put diacritical marks or fail in correctly putting them. Stop word elimination: To not have a huge index meaningless words like 'and', 'the' or 'for' should not be indexed at all. Dictionary substitution (aka: stem words): Similar words should be indexed as one. For example, instances of 'hungrily' and 'hungry' should be replaced with 'hunger'. Phrase search: If I have the text 'Hello world!' a search of '"world hello"' should not match it but a search of '"hello world"' should match. Search all fields (in multifield documents) if no field specified (not just a default field) Auto-completion in search results while typing to give popular searches. (just like Google Suggest) How may I configure a full-text-search engine to behave as much as possible as Google? (I am mostly interested in Open Source, Java and in particular Lucene)

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• How to determine which inheriting class is using an abstract class's methods.

  - by Kin

  In my console application have an abstract Factory class "Listener" which contains code for listening and accepting connections, and spawning client classes. This class is inherited by two more classes (WorldListener, and MasterListener) that contain more protocol specific overrides and functions. I also have a helper class (ConsoleWrapper) which encapsulates and extends System.Console, containing methods for writing to console info on what is happening to instances of the WorldListener and MasterListener. I need a way to determine in the abstract ListenerClass which Inheriting class is calling its methods. Any help with this problem would be greatly appreciated! I am stumped :X Simplified example of what I am trying to do. abstract class Listener { public void DoSomething() { if(inheriting class == WorldListener) ConsoleWrapper.WorldWrite("Did something!"); if(inheriting class == MasterListener) ConsoleWrapper.MasterWrite("Did something!"); } } public static ConsoleWrapper { public void WorldWrite(string input) { System.Console.WriteLine("[World] {0}", input); } } public class WorldListener : Listener { public void DoSomethingSpecific() { ConsoleWrapper.WorldWrite("I did something specific!"); } } public void Main() { new WorldListener(); new MasterListener(); } Expected output [World] Did something! [World] I did something specific! [Master] Did something! [World] I did something specific!

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• Updating entity fields in app engine development server

  - by Joey

  I recently tried updating a field in one of my entities on the app engine local dev server via the sdk console. It appeared to have updated just fine (a simple float). However, when I followed up with a query on the entity, I received an exception: "Items in the mSomeList list must all be Key instances". mSomeList is just another list field I have in that entity, not the one I modified. Is there any reason manually changing a field would adversely throw something off such that the server gets confused? Is this a known bug? I wrote an http handler to alter the field through server code and it works fine if I take that approach. Update: (adding details) I am using the python google app engine server. Basically if I go into the Google App Engine Launcher and press the SDK Console button, then go into one of my entities and edit a field that is a float (i.e. change it from 0 to 3.5, for instance), I get the "Items in the mMyList list must all be Key instance" suddenly when I query the entity like this: query = DataModels.RegionData.gql("WHERE mRegion = :1", region) entry = query.get() the RegionData entity is what has the mMyList member. As mentioned previously, if I do not manually change the field but rather do so through server code, i.e. query = DataModels.RegionData.gql("WHERE mRegion = :1", region) entry = query.get() entry.mMyFloat = 3.5 entry.put() Then it works.

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• Dynamically generate client-side HTML form control using JavaScript and server-side Python code in Google App Engine

  - by gisc

  I have the following client-side front-end HTML using Jinja2 template engine: {% for record in result %} <textarea name="remark">{{ record.remark }}</textarea> <input type="submit" name="approve" value="Approve" /> {% endfor %} Thus the HTML may show more than 1 set of textarea and submit button. The back-end Python code retrieves a variable number of records from a gql query using the model, and pass this to the Jinja2 template in result. When a submit button is clicked, it triggers the post method to update the record: def post(self): if self.request.get('approve'): updated_remark = self.request.get('remark') record.remark = db.Text(updated_remark) record.put() However, in some instances, the record updated is NOT the one that correspond to the submit button clicked (eg if a user clicks on record 1 submit, record 2 remark gets updated, but not record 1). I gather that this is due to the duplicate attribute name remark. I can possibly use JavaScript/jQuery to generate different attribute names. The question is, how do I code the back-end Python to get the (variable number of) names generated by the JavaScript? Thanks.

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• Updating Android Tab Icons

  - by lnediger

  I have an activity which has a TabHost containing a set of TabSpecs each with a listview containing the items to be displayed by the tab. When each TabSpec is created, I set an icon to be displayed in the tab header. The TabSpecs are created in this way within a setupTabs() method which loops to create the appropriate number of tabs: TabSpec ts = mTabs.newTabSpec("tab"); ts.setIndicator("TabTitle", iconResource); ts.setContent(new TabHost.TabContentFactory( { public View createTabContent(String tag) { ... } }); mTabs.addTab(ts); There are a couple instances where I want to be able to change the icon which is displayed in each tab during the execution of my program. Currently I am deleting all the tabs, and calling the above code again to re-create them. mTabs.getTabWidget().removeAllViews(); mTabs.clearAllTabs(true); setupTabs(); Is there a way to replace the icon that is being displayed without deleting and re-creating all of the tabs?

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• django-cms lighttpd redirect domain to url

  - by Robert

  Hello, I am using djano-cms for my site, but instead of language alias /en/ /de/ I need to use another domain. I would like to avoid running multiple django instances, and instead I would like to use lighttpd redirects if possible. I would like requests coming to domain2.com getting data from domain.com/en . The best would be if the user entering: domain2.com/offer got transparently data from domain.com/en/offer Tried many solutions with url.redirect, url.rewrite but none seems to work as desired. Also tried with: http://stackoverflow.com/questions/261904/matching-domains-with-regex-for-lighttpd-mod-evhost-www-domain-com-domain-com but that didn't work. Please help. This is my lighttpd configuration. $HTTP["host"] == "^domain2\.com" { url.redirect = ("^/(.*)" => "http://domain.com/en/$1") } $HTTP["host"] =~ "^domain\.com" { server.document-root = "/var/www/django/projects/domain/" accesslog.filename = "/var/log/lighttpd/domain.log-access.log" server.errorlog = "/var/log/lighttpd/www.domain-error.log" fastcgi.server = ( "/domain-service.fcgi" => ( "main" => ( "socket" => "/tmp/django-domain.sock", "check-local" => "disable", ) ), ) alias.url = ( "/media/" => "/var/www/django/projects/domain/media/", ) url.rewrite-once = ( "^(/site_media.*)$" => "$1", "^(/media.*)$" => "$1", "^/favicon\.ico$" => "/media/favicon.ico", "^(/.*)$" => "/domain-service.fcgi$1", } Thanks

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• Handling Application Logic in Multiple AsyncTask onPostExecute()s

  - by stormin986

  I have three simultaneous instances of an AsyncTask for download three files. When two particular ones finish, at the end of onPostExecute() I check a flag set by each, and if both are true, I call startActivity() for the next Activity. I am currently seeing the activity called twice, or something that resembles this type of behavior. Since the screen does that 'swipe left' kind of transition to the next activity, it sometimes does it twice (and when I hit back, it goes back to the same activity). It's obvious two versions of the activity that SHOULD only get called once are being put on the Activity stack. The only way I can find that this is possible is if both AsyncTasks' onPostExecute() executed SO simultaneously that they were virtually running the same lines at the same time, since I set the 'itemXdownloaded' flag to true right before I check for both and call startActivity(). But this is happening enough that it's very hard for me to believe that both downloads are finishing precisely at the same time and having their onPostExecute()s so close together... Any thoughts on what could be going on here? General gist of code (details removed, ignore any syntactical errors I may have edited in): // In onPostExecute() switch (downloadID) { case DL1: dl1complete = true; break; case DL2: dl2complete = true; break; case DL3: dl3complete = true; break; } // If 1 and 2 are done, move on (DL3 still going in background) if ( downloadID != DL3 && dl1complete && dl2complete) { ParentClass.this.startActivity(new Intent(ParentClass.this, NextActivity.class)); }

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• Serializing Configurations for a Dependency Injection / Inversion of Control

  - by Joshua Starner

  I've been researching Dependency Injection and Inversion of Control practices lately in an effort to improve the architecture of our application framework and I can't seem to find a good answer to this question. It's very likely that I have my terminology confused, mixed up, or that I'm just naive to the concept right now, so any links or clarification would be appreciated. Many examples of DI and IoC containers don't illustrate how the container will connect things together when you have a "library" of possible "plugins", or how to "serialize" a given configuration. (From what I've read about MEF, having multiple declarations of [Export] for the same type will not work if your object only requires 1 [Import]). Maybe that's a different pattern or I'm blinded by my current way of thinking. Here's some code for an example reference: public abstract class Engine { } public class FastEngine : Engine { } public class MediumEngine : Engine { } public class SlowEngine : Engine { } public class Car { public Car(Engine e) { engine = e; } private Engine engine; } This post talks about "Fine-grained context" where 2 instances of the same object need different implementations of the "Engine" class: http://stackoverflow.com/questions/2176833/ioc-resolve-vs-constructor-injection Is there a good framework that helps you configure or serialize a configuration to achieve something like this without hard coding it or hand-rolling the code to do this? public class Application { public void Go() { Car c1 = new Car(new FastEngine()); Car c2 = new Car(new SlowEngine()); } } Sample XML: <XML> <Cars> <Car name="c1" engine="FastEngine" /> <Car name="c2" engine="SlowEngine" /> </Cars> </XML>

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• Trait, FunctionN, or trait-inheriting-FunctionN in Scala?

  - by Willis Blackburn

  I have a trait in Scala that has a single method. Call it Computable and the single method is compute(input: Int): Int. I can't figure out whether I should Leave it as a standalone trait with a single method. Inherit from (Int = Int) and rename "compute" to "apply." Just get rid of Computable and use (Int = Int). A factor in favor of it being a trait is that I could usefully add some additional methods. But of course if they were all implemented in terms of the compute method then I could just break them out into a separate object. A factor in favor of just using the function type is simplicity and the fact that the syntax for an anonymous function is more concise than that for an anonymous Computable instance. But then I've no way to distinguish objects that are actually Computable instances from other functions that map Int to Int but aren't meant to be used in the same context as Computable. How do other people approach this type of problem? No right or wrong answers here; I'm just looking for advice.

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• How do I create a class repository in Java and do I really need it?

  - by Roman

  I have a large number of objects which are identified by names (strings). So, I would like to have a kind of mapping from object name to the class instances. I was told that in this situation I can use a "repository" class which works like that: Server myServer = ServerRepository.getServer("NameOfServer"); So, if there is already an object (sever) with the "NameOfServer" it will be returned by the "getServer". If such an object does not exist yet, it will be created and returned by the "getServer". So, my question is how to program such a "repository" class? In this class I have to be able to check if there is an instance of a given class such that it has a given value of a given field. How can I do it? I need to have a kind of loop over all existing object of a given class? Another part of my question is why I cannot use associative arrays (associative container, map, mapping, dictionary, finite map)? (I am not sure how do you call it in Java) In more details, I have an "array" which maps names of objects to objects. So, whenever I create a new object, I add a new element to the array: myArray["NameOfServer"] = new Server("NameOfServer").

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• Do all the HTML5 storage systems work together ?

  - by azera

  While there are a lot of good stuff about html5, one thing I don't get is the redondant storage mechanism, first there is localstorage and sessionstorage, which are key value stores, one is for one instance of the app ("one tab"), and the other works for all the instances of that application so they can share data. Both are saved when you close your browser and have a limited size (usually 5MB), that's great and everything would be nice if we stopped there. But then there is the "Web SQL Database", which has the same security system as the localstorage, the same size limit, the same everything except it works like/is sqlite, with tables and sql syntax and all of that. And the bummer is, they don't work on the same data at all ! This is not two way to access your data, this is really two storage for every html 5 app out there (not created by default yes, but still you see my point). What I would like to know is, is there a reason for both of this mechanisms to exist at the same time ? Or did they just look at sql and nosql movement to pick the best then went "screw it let's add both !" ? Why not implement local/session storage as a table inside web sql db ?

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• Strange JPA one-to-many behavior when trying to set the "many" on the "one" entity

  - by errr

  I've mapped two entities using JPA (specifically Hibernate). Those entities have a one-to-many relationship (I've simplified for presentation): @Entity public class A { @ManyToOne public B getB() { return b; } } @Entity public Class B { @OneToMany(mappedBy="b") public Set<A> getAs() { return as; } } Now, I'm trying to create a relationship between two instances of these entities by using the setter of the one-side/not-owner-side of the relationship (i.e the table being referenced to): em.getTransaction().begin(); A a = new A(); B b = new B(); Set<A> as = new HashSet<A>(); as.add(a); b.setAs(as); em.persist(a); em.persist(b); em.getTransaction().commit(); But then, the relationship isn't persisted to the DB (the row created for entity A isn't referencing the row created for entity B). Why is it so? I'd excpect it to work. Also, if I remove the "mappedBy" property from the @OneToMany annotation it will work. Again - why is it so? and what are the possible effects for removing the "mappedBy" property?

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• Java abstract visitor - guarantueed to succeed? If so, why?

  - by disown

  I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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• Avoiding mass propagation of properties and events for exposure to ViewModels.

  - by firoso

  I have an MVVM application I am developing that is to the point where I'm ready to start putting together a user interface (my client code is largely functional) I'm now running into the issue that I'm trying to get my application data to where I need it so that it can be consumed by the view model and then bound to the view. Unfortunately, it seems that I've either got a few structural oversights, or I'm just going to have to face the reality that I need to be propogating events and raising excessive amounts of errors to notify view models that thier properties have changed. Let me go into some examples of my issue: I have a class "Unit" contained in a class "Test", contained in a class "Session" contained in a class "TestManager" which is contained in "TestDataModel" which is utilized by "TestViewModel" which is databound to by my "TestView" .... WHOA. Now, consider that Unit (the bottom of the heiarchy) has a property called "Results" that is updated periodically, I want to expose that to my viewmodel and then databind it to my view, trouble is, the only way I can really think to do this is to perpetuate events WAY up a chain that say "I've been updated!" and then request the new value... This seems like an aweful way to do this. Alternatively, I could register a static event and raise it, and have the appropriate "Unit view model" grab the event and request the update. This SEEMS better... but... static events? Is that a taboo idea? Also, having an expression like: TestDataModel.TestManager.Session.Test.Unit.Results[i] Seems REALLY gross to have on a View Model. I know this all reeks of a bad design issue, but I can't figure out what I did wrong? Should I be using more singleton/container controlled lifetimes type objects? Register object instances with static helper containers? Obviously these are hard questions to answer without being intimate with the existing structure, but if you've run into situations like this, what did you do to refactor? Should I just live with this, add mass events, and propogate them?

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