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  • What types of objects should the ViewModel reference in the MVVM pattern?

    - by Blanthor
    I've seen quite a few examples of MVVM. I can see that the View should reference the ViewModel. I've seen recently an example of a ViewModel referencing a View, which seems wrong to me, as it would result in tighter coupling. Given that ViewModel is often described as an intermediary between the View and the Model, is there more to the ViewModel than a facade to domain objects? I hope I used the term "facade" correctly here.

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  • C++ Singleton design pattern.

    - by Artem Barger
    Recently I've bumped into realization/implementation of Singleton design pattern for C++. It has looked in the following way (I have adopted it from real life example): // a lot of methods is omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that instance field is initiated on the heap, that means there is a memory allocation. That is completely unclear for me is when does exactly memory is going to be deallocated? Or there is a bug and memory leak? It seems like there is a problem in implementation. PS. And main question how to implement it in the right way?

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  • Manually Dispatching a DocumentEvent for testing UI element validation code

    - by Bassam
    Hi. I'm testing a Swing GUI application using the UISpec4J testing framework. I'm testing validation code on a JTextField, but the framework does not support focus-change events, as it runs the application in a headless fashion. The text field has a DocumentEvent attached to it that activates the validation code. I'm trying to figure out how to dispatch the document event manually to activate the validation code. Trying to dispatch focus or mouse events manually haven't been working for me. Thanks for any help!

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  • What's the proper approach for writing multi-path "story" flows?

    - by Basiclife
    Hi, I wonder if you can help me. I'm writing a game (2d) which allows players to take multiple routes, some of which branch/merge - perhaps even loop. Each section of the game will decide which section is loaded next. I'm calling each section an IStoryElement - And I'm wondering how best to link these elements up in a way that is easily changed/configured and at the same time, graphable I'm going to have an engine/factory assembly which will load the appropriate StoryElement(s) based on various config options. I initially planned to give each StoryElement a NextElement() As IStoryElement property and a Completed() event. When the vent fires, the engine reads the NextElement property to find the next StoryElement. The downside to this is that if I ever wanted to graph all the routes through the game, I would be unable to - I couldn't determine all possible targets for each StoryElement. I considered a couple of other solutions but they all feel a little clunky - eg Do I need an additional layer of abstraction? ie StoryElementPlayers or similar - Each one would be responsible for stringing together multiple StoryElement perhaps a Series and a ChoicePlayer with each responsible for graphing its own StoryElement - But this will just move the problem up a layer. In short, I need some way of emulating a simple but dynamic workflow (but I'd rather not actually use WWF). Is there a pattern for something this simple? All the ones I've managed to find relate to more advanced control flow (parallel processing, etc.)

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  • Stored Procedure or calculations via IQueryable?

    - by Shawn Mclean
    This is a question that is based on choosing performance over design practices. If I have a method that will be executed many times a second; public static IQueryable<IPerson> InRadius(this IQueryable<IPerson> query, Coordinate center, double radius) { return (from u in query where CallHeavyMathFormula(u, center, radius) select u); } This extension method for IQueryable generates a SQL that does some heavy maths calculation (Cosine, Sine, etc). This would mean the application sends 1-2KB of sql to the server per call. I've heard of placing all application logic, in your application. I also would like to change to a database such as azure or one of those scalable databases in the future. How do I handle something like this? Should I leave it as it is now or write stored procedures? How do applications like twitter or facebook do it?

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  • Beginner Design pattern question (Web Services involved)

    - by zombie
    Hi all ! I am a noob to web services world. I need to develop a login validator module and expose it as a service. I want it to be service independent, i.e I should have the option of exposing it as a SOAP service or REST service in the future. What pattern should I follow ? Sorry if I am unclear in my requirements, I can clarify as per need. Thanks !! Edit : I am using Eclipse as an IDE and Jersey libraries. I am not into any framework, simply using the MVC pattern. I find a lot of difference between SOAP ann REST methods, so I want my methods to be implementation independent - i.e I should be easily able to use my method through a SOAP or REST service call as per need. What should I do for maximum flexibility ?

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  • What are the best practices for writing maintainable CSS?

    - by Art
    I am just starting to explore this area and wonder what are the best practices when it comes to production of clean, well-structured and maintainable CSSes. There seems to be few different approaches to structuring CSS rules. One of the most commonly encountered ones I saw was throwing everything together in one rule, i.e. margins, borders, typefaces, backgrounds, something like this: .my-class { border-top:1px solid #c9d7f1; font-size:1px; font-weight:normal; height:0; position:absolute; top:24px; width:100%; } Another approach I noticed employed grouping of properties, say text-related properties like font-size, typeface, emphasis etc goes into one rule, backgrounds go into other, borders/margins go into yet another one: .my-class { border-top:1px solid #c9d7f1; } .my-class { font-size:1px; font-weight:normal; } .my-class { height:0; top:24px; width:100%; position:absolute; } I guess I am looking for a silver bullet here which I know I am not going to get, bet nevertheless - what are the best practices in this space?

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  • Name the pattern - Create, Set, Execute, Destroy?

    - by Seb Nilsson
    I somewhere heard that the .NET Framework was built around specific pattern, which they tried to uphold as much as possible. var rsa = new RSACryptoServiceProvider(); // Create rsa.ImportParameters(GetParameters()); // Set byte[] encrypted = rsa.Encrypt(data, true); // Execute // Destroyed by garbage-collector Are there any variants of this? What are the general pros and cons?

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  • Approaching Java from a Ruby perspective

    - by Travis
    There are plenty of resources available to a Java developer for getting a jump-start into Ruby/Rails development. The reverse doesn't appear to be true. What resources would you suggest for getting up-to-date on the current state of java technologies? How about learning how to approach DRY (don't repeat yourself) without the use of metaprogramming? Or how to approach various scenarios where a ruby developer is used to passing in a function (proc/lambda/block) as an argument (callbacks, etc)?

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  • Design pattern to separate messages from actual process.

    - by Manish Gupta
    I am having a C# application to sync data between PC and palm devices. There are codes written like below: showMessage("synchronizing Table1"); Sync(destTable1,sourceTable1); Sync(destTable2,sourceTable2); showMessage("synchronizing Table2"); // more code How do I separate the actual process of synchronizing from displaying message? Which design pattern to follow? Thanks in advance...

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  • Is there a design pattern that expresses objects (an their operations) in various states?

    - by darren
    Hi I have a design question about the evolution of an object (and its state) after some sequence of methods complete. I'm having trouble articulating what I mean so I may need to clean up the question based on feedback. Consider an object called Classifier. It has the following methods: void initialise() void populateTrainingSet(TrainingSet t) void pupulateTestingSet(TestingSet t) void train() void test() Result predict(Instance i) My problem is that these methods need to be called in a certain order. Futher, some methods are invalid until a previous method is called, and some methods are invalid after a method has been called. For example, it would be invalid to call predict() before test() was called, and it would be invalid to call train() after test() was called. My approach so far has been to maintain a private enum that represents the current stateof the object: private static enum STATE{ NEW, TRAINED, TESTED, READY}; But this seems a bit cloogy. Is there a design pattern for such a problem type? Maybe something related to the template method.

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  • Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

    - by Daniel Lew
    I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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  • Using a regex pattern to find revision numbers from a svn merge

    - by zyzy
    svn diff -rXX:HEAD Will give me a format like this, if there has been a merge between those revisions: Merged /<branch>:rXXX,XXX-XXX or Merged /<branch>:rXXX I'm not very familiar with regex and am trying to put together a pattern which will match all the numbers (merged revision numbers) AFTER matching the "Merged /branch:r" part. So far I have this to match the first part: [Mm]erged.*[a-zA-Z]:r Thanks in adv. for the help :)

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  • Singleton & Multithreading in Java

    - by vivek jagtap
    What is the preferred way to work with Singleton class in multithreaded environment? Suppose if I have 3 thread, and all they try to access getInstance() method of singleton class at the same time - What would happen if no synchronization is maintained? Is it good practice to use synchronized getInstance() method or use synchronized block inside getInstance(). Please advise if there is any other way out.

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  • Why represent shopping carts and order invoices differently in a domain model?

    - by Todd
    I've built some shopping cart systems in the past, but I always designed them such that the final order invoice is just a shopping cart that has been marked as "purchased". All the logic for adding/removing/changing items in a cart is also the logic for the order. All data is stored in the same tables in the database. But it seems this is not the proper way to design an e-commerce site.. Can someone explain the benefit of separating the shopping cart from invoices in the domain model? It seems to me this would lead to a lot of duplicated code, an extra set of tables in the database, and make it harder to maintain in the event the system need to start accommodating more complicated orders (like specifying selected options for an item which may or may not change the price/availability/shipping time of the order). I'm assuming I just haven't seen the light, as every book and other example I see seems to separate these two seemingly similar concerns -- but I can't find any explanation as to the benefit of doing such! It's also the case in the systems that I design that changes are often made after the initial order is confirmed. It's not uncommon for items to be removed, replaced, or added afterwards (but prior to fulfillment).

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  • Find recipes that can be cooked from provided ingridients

    - by skaurus
    Sorry for bad English :( Suppose i can preliminary organize recipes and ingredients data in any way. How can i effectively conduct search of recipes by user-provided ingredients, preferably sorted by max match - so, first going recipes that use maximum of provided ingridients and do not contain any other ingrs, after them recipes that uses less of provided set and still not any other ingrs, after them recipes with minimum additional requirements and so on? All i can think about is represent recipe ingridients like bitmasks, and compare required bitmask with all recipes, but it is obviously a bad way to go. And related things like Levenstein distance i don't see how to use here. I believe it should be quite common task...

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  • C++ error message output format

    - by sub
    If I want to trigger an error in my interpreter I call this function: Error( ErrorType type, ErrorSeverity severity, const char* msg, int line ); However, with that I can only output Name error: Undefined variable in line 1 instead of Name error: Undefined variable 'someVariableName' in line 1 I'm working entirely with strings (except for the error messages as they all are constant at the moment), so sprintf won't work. What is the best way to create an efficient error function that can output a constant message combined with a string that describes which object, e.g.: a non-existing variable, triggered the error?

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  • Accessing the "super of this" in Java

    - by gerdemb
    This is what I'm doing now. Is there a better way to access the super class? public class SearchWidget { private void addWishlistButton() { final SearchWidget thisWidget = this; button.addClickHandler(new ClickHandler() { public void onClick(ClickEvent event) { // A better way to access the super class? // something like "this.super" ...? workWithWidget(thisWidget); } } } } I'm programming with Google Web Toolkit, but I think this is really a generic Java question.

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  • ASP.NET MVC Filters: How to set Viewdata for Dropdown based on action parameter

    - by CRice
    Hi, Im loading an entity 'Member' from its id in route data. [ListItemsForMembershipType(true)] public ActionResult Edit(Member someMember) {...} The attribute on the action loads the membership type list items for a dropdown box and sticks it in viewdata. This is fine for add forms, and search forms (it gets all active items) but I need the attribute to execute BASED ON THE VALUE someMember.MembershipTypeId, because its current value must always be present when loading the item (i.e. all active items, plus the one from the loaded record). So the question is, what is the standard pattern for this? How can my attribute accept the value or should I be loading the viewdata for the drop down in a controller supertype or during model binding or something else? It is in an attribute now because the code to set the viewdata would otherwise be duplicated in each usage in each action.

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  • What is the correct approach to using GWT with persistent objects?

    - by dankilman
    Hi, I am currently working on a simple web application through Google App engine using GWT. It should be noted that this is my first attempt at such a task. I have run into to following problem/dilema: I have a simple Class (getters/setters and nothing more. For the sake of clarity I will refer to this Class as DataHolder) and I want to make it persistent. To do so I have used JDO which required me to add some annotations and more specifically add a Key field to be used as the primary key. The problem is that using the Key class requires me to import com.google.appengine.api.datastore.Key which is ok on the server side, but then I can't use DataHolder on the client side, because GWT doesn't allow it (as far as I know). So I have created a sister Class ClientDataHolder which is almost identical, though it doesn't have all the JDO annotations nor the Key field. Now this actually works but It feels like I'm doing something wrong. Using this approach would require maintaining to separate classes for each entity I wish to have. So my question is: Is there a better way of doing this? Thank you.

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  • How can I use Object Oriented Javascript to interact with HTML Objects

    - by Steve
    I am very new to object orientated javascript, with experience writing gui's in python and java. I am trying to create html tables that I can place in locations throughout a webpage. Each html table would have two css layouts that control if it is selected or not. I can write all of the interaction if I only have one table. It gets confusing when I have multiple tables. I am wondering how to place these tables throughout a blank webpage and then access the tables individually. I think I am having trouble understanding how inheritance and hierarchy works in javascript/html. NOTE: I am not asking how to make a table. I am trying to dynamically create multiple tables and place them throughout a webpage. Then access their css independently and change it (move them to different locations or change the way the look, independently of the other tables).

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