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• How do I reuse a state machine in a slightly different way?

  - by JoJo

  Problem I have a big state machine. The design requirements of the project have changed such that I need to re-use this state machine in another place. All the states remain the same in this new place, but a few states run slightly different stuff. What design pattern allows me to reuse this state machine? Motivation I am building a video player. It is modeled by a state machine with these states: stopped, loading, playing, paused, crashed, and some more... This video player needs to be used on two web pages. When the player crashes on the first page, it should show an error message below. If the player crashes on the second page, the error message should appear in the center of the video and pulsate a few times.

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• Is OOP becoming easier or harder?

  - by tunmise fasipe

  When the concepts of Object Oriented Programming were introduced to programmers years back it looks interesting and programming was cleaner. OOP was like this Stock stock = new Stock(); stock.addItem(item); stock.removeItem(item); That was easier to understand with self-descriptive name. But now OOP, with pattern like Data Transfer Objects (or Value Objects), Repository, Dependency Injection etc, has become more complex. To achieve the above you may have to create several classes (e.g. abstract, factory, DAO etc) and Implement several interfaces Note: I am not against best practices that makes Collaboration, Testing and Integration easier

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• How to generate "language-safe" UUIDs?

  - by HappyDeveloper

  I always wanted to use randomly generated strings for my resources' IDs, so I could have shorter URLs like this: /user/4jz0k1 But I never did, because I was worried about the random string generation creating actual words, eg: /user/f*cker. This brings two problems: it might be confusing or even offensive for users, and it could mess with the SEO too. Then I thought all I had to do was to set up a fixed pattern like adding a number every 2 letters. I was very happy with my 'generate_safe_uuid' method, but then I realized it was only better for SEO, and worse for users, because it increased the ratio of actual words being generated, eg: /user/g4yd1ck5 Now I'm thinking I could create a method 'replace_numbers_with_letters', and check that it haven't formed any words against a dictionary or something. Any other ideas? ps. As I write this, I also realized that checking for words in more than one language (eg: english and french, spanish, etc) would be a mess, and I'm starting to love numbers-only IDs again.

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• What version will be chosen by MSXML2.XMLHTTP request, without version suffix? [migrated]

  - by jayarjo

  Probably every web developer is familiar with a pattern like this: var xmlHttp = null; if (window.XMLHttpRequest) { // If IE7, Mozilla, Safari, and so on: Use native object. xmlHttp = new XMLHttpRequest(); } else { if (window.ActiveXObject) { // ...otherwise, use the ActiveX control for IE5.x and IE6. xmlHttp = new ActiveXObject('MSXML2.XMLHTTP'); } } But the question is - if there are multiple MSXML versions available on the client's PC (let's say 3.0, 5.0, 6.0), which one of them will be chosen by MSXML2.XMLHTTP call (notice no version suffix at the end)? Will it be the latest or - not necessarily? And a side-question - is it possible to check which version was chosen?

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• What is this called?

  - by robertlewis2001

  I'm hoping there's a book or something out there for me to get... If I have a class that has Collection as an instance variable, what is that method of coding called? A design pattern? If so, where can I find more information on it? As I've been working with this mentor, he's really helped me understand my programming weakness and that weakness is thinking in terms of collections or relationships between objects. It just seems so difficult for me right now and I need to read to become smarter. My mentor is a great guy, but he gets frustrated when I start asking lots of questions, so I'm starting to feel like I need to learn more on my own. public class Evaluation { private List<Criterion> criterion = null; public Evaluation() { criterion = new List<Criterion>(); } }

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• My laptop doesn't always boot to login

  - by GUI Junkie

  I have an recurring problem. Every once in a while, no pattern, the laptop freezes during boot. Sometimes at a black screen, sometimes a black screen with a not blinking cursor... The solution is to power down the laptop, cross my fingers and boot again. Sometimes it takes four or five reboots, but in the end I always get the system up and running. What bugs me is the fact that the boot is not 'stable' in a sense that apparently it doesn't always do exactly the same thing. I'm still using 10.10. The question is whether there is anything that can be done to make the system stable. (Does 11.04 have the same issue?) Edit: Today the same thing happened. First a black screen with a non blinking cursor. Second a black screen. Third login screen.

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• Repositories and the Save Method

  One of the questions I've been getting lately goes like this: Should a Repository class have a Save method? And the standard answer: It depends. It's hard to keep track of all the different approaches to implementing the repository pattern these days, but I assume when someone asks me this type of question they are thinking of using code like this: var employee = new Employee(); employeeRepository.Save(employee); var account = new Account(); accountRepository.Save(account); This...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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• Processing a list of atomic operations, allowing for interruptions

  - by JDB

  I'm looking for a design pattern that addresses the following situation: There exists a list of tasks that must be processed. Tasks may be added at any time. Each task is wholly independent from all other tasks. The order in which tasks are processed has no effect on the overall system or on the tasks themselves. Every task must be processed once and only once. The "main" process which launches the task processors may start and stop without warning. When stopped, the "main" process loses all in-memory data. Obviously this is going to involve some state, but are there any design patterns which discuss where and how to maintain that state? Are there any relevant anti-patterns? Named patterns are especially helpful so that we can discuss this topic with other organizations without having to describe the entire problem domain.

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• Why do most of us use 'i' as a loop counter variable?

  - by kprobst

  Has anyone thought about why so many of us repeat this same pattern using the same variable names? for (int i = 0; i < foo; i++) { // ... } It seems most code I've ever looked at uses i, j, k and so on as iteration variables. I suppose I picked that up from somewhere, but I wonder why this is so prevalent in software development. Is it something we all picked up from C or something like that? Just an itch I've had for a while in the back of my head.

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• MVC? patterns for game development? [closed]

  - by davivid

  Possible Duplicate: MVC-like compartmentalization in games? I am thinking of the best way to structure my project and was thought a MVC style pattern would be appropriate. Would be correct having the model handle the majority and basically being the game engine? Are there any standardised patterns recommended for simple game development? Model / Game Engine Data: Level Design, Chat feeds, etc Game Status: Player status, Enemy status, World Status etc etc. Engine: Physics, Collisions, AI View 3D: Gameplay, Camera, Rendering... 2D: UI etc Controller: Player Input UI Input

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• What are the caveats of the event system built on Messenger rather than on classic .NET events?

  - by voroninp

  MVVM Light and PRISM offer messenger to implement event system. the approximate interface looks like the following one: interface Messanger { void Subscribe<TMessageParam>(Action<TMessageParam> action); void Unsubscribe<TMessageParam>(Action<TMessageParam> action); void Unsubscribe<TMessageParam>(objec actionOwner); void Notify<TMessageParam>(TMessageParam param); } Now this model seems beneficial comparing to classic .net events. It works well with Dependency Injection. Actions are stored as weak references so memory leaks are avioded and unsubscribe is not a must. The only annoyance is the need to declare new TMessageParam for each specific message. But everything comes at a cost. And what I'm really worried about is that I see no shortcomings of this approach. Has anoyne the experience of some troubles with this design pattern?

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• Get and set accessors do they protect different instances of a variable?

  - by Chris Halcrow

  The standard method of implementing get and set accessors in C# and VB.NET is to use a public property to set and retrieve the value of a corresponding private variable. Am I right in saying that this has no effect of different instances of a variable? By this I mean, if there are different instantiations of an object, then those instances and their properties are completely independent right? So I think my understanding is correct that setting a private variable is just a construct to be able to implement the get and set pattern? Never been 100% sure about this.

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• Pooling (Singleton) Objects Against Connection Pools

  - by kolossus

  Given the following scenario A canned enterprise application that maintains its own connection pool A homegrown client application to the enterprise app. This app is built using Spring framework, with the DAO pattern While I may have a simplistic view of this, I think the following line of thinking is sound: Having a fixed pool of DAO objects, holding on to connection objects from the pool. Clearly, the pool should be capable of scaling up (or down depending on need) and the connection objects must outnumber the DAOs by a healthy margin. Good Instantiating brand new DAOs for every request to access the enterprise app; each DAO will attempt to grab a connection from the pool and release it when it's done. Bad Since these are service objects, there will be no (mutable) state held by the objects (reduced risk of concurrency issues) I also think that with #1, there should be little to no resource contention, while in #2, there'll almost always be a DAO waiting to be serviced. Is my thinking correct and what could go wrong?

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• Is the UX affected negatively by fully cacheable pages?

  - by ChocoDeveloper

  I want to have fully cacheable pages in my websites, but one cannot do that if they contain user-specific data, like the userbar or things in the UI that can change depending on the permissions the user has. So I was thinking whether it was possible to pull everything that is user-specific via ajax, and update the UI accordingly. But I'm worried that this might be annoying for the user, and also it might be difficult to develop. What do you think? Is there a pattern or something I can follow to deal with this?

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• Fujitsu B6220 laptop, sometimes my desktop freezes upon resume from standby

  - by user89756

  I installed Ubuntu 11.10 on my Fujitsu Lifebook B6220 laptop just before 12.04 was released. I can not remember if I had this issue with Ubuntu 11.10 as I updated the install to 12.04 about a week after 12.04 came out. My problem is that sometimes upon resume from standby my desktop is frozen. The keyboard, touch pad, and touchscreen work, but there is no response from the desktop. I can ctrl-alt-f2 and log in and then from there I just reboot the computer. This happens about 50% of the time when I resume from standby but I have not noticed a distinct pattern. I have thought about reinstalling 12.04, since I upgraded 11.10 to 12.04 instead of a fresh install. But I have customized my laptop a lot and I would prefer to avoid reinstalling it, I'm not even sure if that would fix it. Anyone have a idea what might be the problem? If I should submit this as a bug, could someone point me in the right direction please? Thanks, Matt

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• How to design 2D collision callback methods?

  - by Ahmed Fakhry

  In a 2D game where you have a lot of possible combination of collision between objects, such as: object A vs object B = object B vs A; object A vs object C = object C vs A; object A vs object D = object D vs A; and so on ... Do we need to create callback methods for all single type of collision? and do we need to create the same method twice? Like, say a bullet hits a wall, now I need a method to penetrate the wall for the wall, and a method to destroy the bullet for the bullet!! At the same time, a bullet can hit many objects in the game, and hence, more different callback methods!!! Is there a design pattern for that?

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• Technical Article: Experimenting with Java Timers

  - by Tori Wieldt

  OTN's new tech article is "Experimenting with Java Timers" by T. Lamine Ba. This article studies time—how Java handles timers and the scheduling of tasks. Java timers are utilities that let you execute threads or tasks at a predetermined future time, and these tasks can be repeated according to a set frequency. The article starts with a simple "Hello World" program in a web application that's composed of JavaServer Pages (JSP) and uses the model-control-view (MVC) design pattern. The IDE used in this article is NetBeans IDE 7.1, but you can use any IDE that supports Java. "Experimenting with Java Timers" demonstrates how to get started scheduling jobs with Java. To learn about Swing timers, check out the Java tutorial "How to Use Swing Timers" and additional information in the Java Platform, Standard Edition 7 API Specification for Class Timer. 

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• Silverlight 4 + RIA Services - Ready for Business: Localizing Business Application

  To continue our series, lets look at localizing our business applications.  In todays global village, it is often no longer OK to support only one language.   Many real world business applications need to support multiple languages.  To demonstrate the pattern, lets look at localizing the Silverlight Business Application Template.   You can download the completed solution.   Here it is in English side-by-side with a localized version (notice the Hebrew is rendered...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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• Can a domain specific language be used to representing the Open SRD

  - by NeoModulus

  I am in the early stages of creating an open source C# library that would allow developers to drop in the open SRD (http://www.d20srd.org/) into an existing project. Abstracted it is a complex set of tightly coupled business rules. Having previously worked on an adaptive object model project for health care risk management I began with that pattern in mind. Due to the high coupling of rules it is becoming apparent that the project may require some kind of scripting. Have started researching DSL implementation I am now considering scraping the adaptive object model for a domain specific language. I have not work with domain specific languages so my question is it reasonable to assume a domain specific language can be used to representing the open SRD?

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• How do you usually manage callbacks in Java using Swing library?

  - by none

  I'm quite new to the Java Swing programming, and GUI development as well. As a beginner, I'm currently reading Design Pattern, but finding what I'm looking for is quite hard, most of the times. So far, I've never had huge problems defining a view hierarchy - I just use to subclass component from component. But the hard-to-do here is how managing callbacks, which often become hard to maintain due to the hard code. During my last projects, I tried to separate GUI, Listener and Callbacker objects which cooperated together, but in this way it was really hard adding new features. So, which kind of best patterns or best practices do you tend to use when trying to maintain, add new features or even worst avoid to hard-code classes which manage callbacks method in this kind of frameworks (mainly Java Swing)?

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• PHP - Data Access Layer

  - by scarpacci

  I am currently reviewing a code base and noticed that a majority of the calls (along with DB connections) are just buried inside the PHP scripts. I would have assumed that like other languages they would have developed some sort of data access layer (Like I would do in .Net or Java) for all of the communication to the DB (or implemented MVC, etc). Is this still a common pattern in PHP or is there alternative methodologies/patterns for this technology? I am just trying to understand why the subs would have developed it this way. Any insight/info on how experienced developers design an approach data access in PHP would be very much appreciated.

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• Web programming, standard way to deal with a response that takes time to complete

  - by wobbily_col

  With normal form submission I use the pattern Post / Redirect / Get, when processing the forms. I have a database application built with Django. I want to allow the users to select a number of items from the database, then launch a computationally intensive task based on those items. I expect the task to take between 10 minutes and 2 hours to complete. Is there a standard approach to dealing with requests like this (i.e. that don't return immediately)? Ideally there would be some way to display the progress.

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• Identifying methods with a specified Id in D [migrated]

  - by Ekyo777

  I want to have specific methods with a specific pattern recognized at compile time and registered along with a specified id trough mixins in a parent class. ex.: take a method 'X' from a class with a predetermined id:5, what I want is that, in a mixin in a parent class, method X will be registered as a delegate with its id to be called later on by its id. What would be the best way to specify the Id considering I want the id to be of type int and only the specified methods to be registered? should I (if it is even possible) do it with a custom annotation pretty much like the @property but with an argument, like: @autoregister(id) void method(...) if it is possible to do it this way, an example or a link to the documentation on how to do it would be nice since I didn't find it in the documentation.

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• Naming convention: field starting with "m" or "s"

  - by Noya

  Hope this question hasn't posted yet... I saw lot of code (for example some Android source code) where fields name start with a "m" while static fields start with "s" Example (taken from Android View class source): private SparseArray<Object> mKeyedTags; private static int sNextAccessibilityViewId; I was wondering what "m" and "s" stand for... maybe is "m" mutable and "s" static? Since it seems that is a largely adopted pattern do you know if there some literature about this kind of naming convention?

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• How can I bind an interface to a class decided by an xml or database configuration at the launch of the application?

  - by ipohfly

  I'm re-working on the design of an existing application which is build using WebForms. Currently the plan is to work it into a MVP pattern application while using Ninject as the IoC container. The reason for Ninject to be there is that the boss had wanted a certain flexibility within the system so that we can build in different flavor of business logic in the model and let the programmer to choose which to use based on the client request, either via XML configuration or database setting. I know that Ninject have no need for XML configuration, however I'm confused on how it can help to dynamically inject the dependency into the system? Imagine I have a interface IMember and I need to bind this interface to the class decided by a xml or database configuration at the launch of the application, how can I achieve that?

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