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  • Clarification on the Strategy Pattern

    - by Holly
    I've just been reading through some basic design patterns, Could someone tell me if the term "strategy pattern" only applies if your implementing a completely abstract interface? What about when your children (concretes?) inherit from a parent class (the strategy?) with some implemented methods and some virtual and/or abstract functions? Otherwise the rest of the implementation, the idea that you can switch between different children at run time, is identical. This is something i'm quite familiar with, i was wondering if you would still call it the Strategy Pattern or if that term only applies to using an interface. Apologies if this question is not appropriate! Or if this is just nitpicking :) I'm still learning and i'm not really sure if design patterns are quite heavily defined within the industry or just a concept to be implemented as you like.

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  • Is it okay to have many Abstract classes in your application?

    - by JoseK
    We initially wanted to implement a Strategy pattern with varying implementations of the methods in a commmon interface. These will get picked up at runtime based on user inputs. As it's turned out, we're having Abstract classes implementing 3 - 5 common methods and only one method left for a varying implementation i.e. the Strategy. Update: By many abstract classes I mean there are 6 different high level functionalities i.e. 6 packages , and each has it's Interface + AbstractImpl + (series of Actual Impl). Is this a bad design in any way? Any negative views in terms of later extensibility - I'm preparing for a code/design review with seniors.

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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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  • TrueCrypt System Favorite Volume doesn't mount automatically on boot

    - by Anders Hovgaard
    I've encrypted my system partition using TrueCrypt and I've read that I can mount my encrypted data partition (TrueCrypt volume) on boot by making it a "System Favorite" and giving it the same password as the system partition. However it doesn't work and I have to mount it manually every time. See this example. I've tried enabling "Cache pre-boot authentication password in driver memory (for mounting of non-system volumes)" in System - Settings, but that didn't change anything either. Any ideas?

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  • Can manager classes be a sign of bad architecture?

    - by Paul
    Lately I've begun to think that having lots of manager classes in your design is a bad thing. The idea hasn't matured enough for me to make a compelling argument, but here's a few general points: I found it's a lot harder for me to understand systems that rely heavily on "managers". This is because, in addition to the actual program components, you also have to understand how and why the manager is used. Managers, a lot of the time, seem to be used to alleviate a problem with the design, like when the programmer couldn't find a way to make the program Just WorkTM and had to rely on manager classes to make everything operate correctly. Of course, mangers can be good. An obvious example is an EventManager, one of my all time favorite constructs. :P My point is that managers seem to be overused a lot of the time, and for no good reason other than mask a problem with the program architecture. Are manager classes really a sign of bad architecture?

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  • When dealing with a static game board, what are some methods to make it more interesting?

    - by Ólafur Waage
    Let's say you have a game board that you look at. It does not move but there is some action going on. For example Chess, Checkers, Solitaire. The game I'm working on is not one of these but it's a good reference. What are some methods you can apply to the game or the design that increases the appeal of the game to the user? Of course you can make it prettier but what are some other methods you can use? For example: Visual cues, game design changes, user interface arrangement, etc.

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  • Passing functions into other functions as parameters, bad practice?

    - by BlueHat
    We've been in the process of changing how our AS3 application talks to our back end and we're in the process of implementing a REST system to replace our old one. Sadly the developer who started the work is now on long term sick leave and it's been handed over to me. I've been working with it for the past week or so now and I understand the system, but there's one thing that's been worrying me. There seems to be a lot of passing of functions into functions. For example our class that makes the call to our servers takes in a function that it will then call and pass an object to when the process is complete and errors have been handled etc. It's giving me that "bad feeling" where I feel like it's horrible practice and I can think of some reasons why but I want some confirmation before I propose a re-work to system. I was wondering if anyone had any experience with this possible problem?

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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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  • Using "public" vars or attributes in class calls, functional approach

    - by marw
    I was always wondering about two things I tend to do in my little projects. Sometimes I will have this design: class FooClass ... self.foo = "it's a bar" self._do_some_stuff(self) def _do_some_stuff(self): print(self.foo) And sometimes this one: class FooClass2 ... self.do_some_stuff(foo="it's a bar") def do_some_stuff(self, foo): print(foo) Although I roughly understand the differences between functional and class approaches, I struggle with the design. For example, in FooClass the self.foo is always accessible as an attribute. If there are numerous calls to it, is that faster than making foo a local variable that is passed from method to method (like in FooClass2)? What happens in memory in both cases? If FooClass2 is preferred (ie. I don't need to access foo) and other attributes inside do not change their states (the class is executed once only and returns the result), should the code then be written as a series of functions in a module?

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  • HTML/CSS plagiarism

    - by luqita
    Hi!! I'm facing an issue here. A customer asked me to copy an exact site, and even though I'm trying to convince him of going for a new design he does not accept it. He loves this design so much (on a side note it's horrible and outdated, but I wouldn't say that to him!) It's been a couple of weeks since we are discussing this and I don't know what to do. Do you have similar experiences? I don't want to lose the customer, he pays well and his jobs are really easy. At the same time, I don't want to put my signature on someone else's work. Any suggestions? Similar experiences? Thank you!

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  • iOS app with a lot of text

    - by rdurand
    I just asked a question on StackOverflow, but I'm thinking that a part of it belongs here, as questions about design pattern are welcomed by the faq. Here is my situation. I have developed almost completely a native iOS app. The last section I need to implement is all the rules of a sport, so that's a lot of text. It has one main level of sections, divided in subsections, containing a lot of structured text (paragraphs, a few pictures, bulleted/numbered lists, tables). I have absolutely no problem with coding, I'm just looking for advice to improve and make the best design pattern possible for my app. My first shot (the last one so far) was a UITableViewController containing the sections, sending the user to another UITableViewController with the subsections of the selected section, and then one strange last UITableViewController where the cells contain UITextViews, sections header help structure the content, etc. What I would like is your advice on how to improve the structure of this section. I'm perfectly ready to destroy/rebuild the whole thing, I'm really lost in my design here.. As I said on SO, I've began to implement a UIWebView in a UIViewController, showing a html page with JQuery Mobile to display the content, and it's fine. My question is more about the 2 views taking the user to that content. I used UITableViewControllers because that's what seemed the most appropriate for a structured hierarchy like this one. But that doesn't seem like the best solution in term of user experience.. What structure / "view-flow" / kind of presentation would you try to implement in my situation? As always, any help would be greatly appreciated! Just so you can understand better the hierarchy, with a simple example : -----> Section 1 -----> SubSection 1.1 -----> Content | -----> SubSection 1.2 -----> Content | -----> SubSection 1.3 -----> Content | | | UINavigationController -------> Section 2 -----> SubSection 2.1 -----> Content | -----> SubSection 2.2 -----> Content | -----> SubSection 2.3 -----> Content | -----> SubSection 2.4 -----> Content | -----> SubSection 2.5 -----> Content | -----> Section 3 -----> SubSection 3.1 -----> Content -----> SubSection 3.2 -----> Content |------------------| |--------------------| |-------------| 1 UITableViewController 3 UITableViewControllers 10 UIViewControllers (3 rows) (with different with a UIWebView number of rows)

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  • Advice on approaching a significant rearrangement/refactoring?

    - by Prog
    I'm working on an application (hobby project, solo programmer, small-medium size), and I have recently redesigned a significant part of it. The program already works in it's current state, but I decided to reimplement things to improve the OO design. I'm about to implement this new design by refactoring a big part of the application. Thing is I'm not sure where to start. Obviously, by the nature of a rearrangement, the moment you change one part of the program several other parts (at least temporarily) break. So it's a little 'scary' to rearrange something in a piece of software that already works. I'm asking for advice or some general guidelines: how should I approach a significant refactoring? When you approach rearranging large parts of your application, where do you start? Note that I'm interested only in re-arranging the high-level structure of the app. I have no intention of rewriting local algorithms.

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  • System Out Of Memory Exception in Production Server

    - by Sachin Gupta
    We have .net application installed on production server. It is using .net FrameWork 3.0 on windows server 2003 with RAM 4 GB. But there is a problem in application while running sometimes it throws system out of memory exception. I am very frustrating with this. Also I am unable to simulate the issue. I had checked all the possibilities which can cause the problem but didn’t get any thing which solve the issue I checked on production server event log found the Out Of Memory Exception also INVALID VIEW STATE logs are there. Look at the following event log which may help to find solutions. Exception information: Exception type: HttpException Exception message: Invalid viewstate. Request information: Request path: /zContest/ScriptResource.axd User: LisaA Is authenticated: True Authentication Type: Forms Thread information: Thread ID: 10 Is impersonating: True Stack trace: at System.Web.UI.Page.DecryptStringWithIV(String s, IVType ivType) at System.Web.UI.Page.DecryptString(String s) at System.Web.Handlers.ScriptResourceHandler.DecryptParameter(NameValueCollection queryString) at System.Web.Handlers.ScriptResourceHandler.ProcessRequestInternal(HttpResponse response, NameValueCollection queryString, VirtualFileReader fileReader) at System.Web.Handlers.ScriptResourceHandler.ProcessRequest(HttpContext context) at System.Web.Handlers.ScriptResourceHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) ------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Event code: 3005 Event message: An unhandled exception has occurred. Process information: Process ID: 5388 Process name: w3wp.exe Exception information: Exception type: OutOfMemoryException Exception message: Exception of type 'System.OutOfMemoryException' was thrown. ------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Please help me out on this

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  • SBS2003 to SBS2011 Migration - Installation Error

    - by Shawn Gradwell
    Microsoft Small Business Server 2003 to 2011 Migration. I followed the Migration Guide from Microsoft and the source server had no errors when running the various tests prior to the migration. I have completed the destination server setup using the Answer File and the server is up and running. It all looks good, I can access Exchange and AD and the only problem is the error message when you log in stating that the setup did not complete and to check the logs. Because all looks good I am continuing the migration to the destination server. I also have to state that this client does not use Sharepoint at all. Do I have to redo everything? Herewith the logs: [4992] 121016.225454.5905: Task: Starting Add User or Group access VSS registry. [4992] 121016.225454.7645: TaskManagement: In TaskScheduler.RunTasks(): The "ConfigureSharePointVSSRegistryTask" Task threw an Exception during the Run() call:System.Security.Principal.IdentityNotMappedException: Some or all identity references could not be translated. at System.Security.Principal.NTAccount.Translate(IdentityReferenceCollection sourceAccounts, Type targetType, Boolean forceSuccess) at System.Security.Principal.NTAccount.Translate(Type targetType) at System.Security.AccessControl.CommonObjectSecurity.ModifyAccess(AccessControlModification modification, AccessRule rule, Boolean& modified) at System.Security.AccessControl.CommonObjectSecurity.AddAccessRule(AccessRule rule) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.AddUsersToAccessRegistry(List`1 names) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.Run(ITaskDataLink dl) at Microsoft.WindowsServerSolutions.TaskManagement.Data.Task.Run(ITaskDataLink dataLink) at Microsoft.WindowsServerSolutions.TaskManagement.TaskScheduler.RunTasks(String taskListId, String stateFileName) [4992] 121016.225454.7655: Setup: An error was encountered on the TME thread: System.Security.Principal.IdentityNotMappedException: Some or all identity references could not be translated. at System.Security.Principal.NTAccount.Translate(IdentityReferenceCollection sourceAccounts, Type targetType, Boolean forceSuccess) at System.Security.Principal.NTAccount.Translate(Type targetType) at System.Security.AccessControl.CommonObjectSecurity.ModifyAccess(AccessControlModification modification, AccessRule rule, Boolean& modified) at System.Security.AccessControl.CommonObjectSecurity.AddAccessRule(AccessRule rule) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.AddUsersToAccessRegistry(List`1 names) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.Run(ITaskDataLink dl) at Microsoft.WindowsServerSolutions.TaskManagement.Data.Task.Run(ITaskDataLink dataLink) at Microsoft.WindowsServerSolutions.TaskManagement.TaskScheduler.RunTasks(String taskListId, String stateFileName) at Microsoft.WindowsServerSolutions.Setup.SBSSetup.ProgressPagePresenter._RunTasks(Object sender, DoWorkEventArgs e) [4956] 121016.225455.0685: Setup: _UnhandledExceptionHandler: Setup encountered an error: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Reflection.TargetInvocationException: The TME thread failed (see the inner exception). ---> System.Security.Principal.IdentityNotMappedException: Some or all identity references could not be translated. at System.Security.Principal.NTAccount.Translate(IdentityReferenceCollection sourceAccounts, Type targetType, Boolean forceSuccess) at System.Security.Principal.NTAccount.Translate(Type targetType) at System.Security.AccessControl.CommonObjectSecurity.ModifyAccess(AccessControlModification modification, AccessRule rule, Boolean& modified) at System.Security.AccessControl.CommonObjectSecurity.AddAccessRule(AccessRule rule) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.AddUsersToAccessRegistry(List`1 names) at Microsoft.WindowsServerSolutions.IWorker.Tasks.ConfigureSharePointVSSRegistryTask.Run(ITaskDataLink dl) at Microsoft.WindowsServerSolutions.TaskManagement.Data.Task.Run(ITaskDataLink dataLink) at Microsoft.WindowsServerSolutions.TaskManagement.TaskScheduler.RunTasks(String taskListId, String stateFileName) at Microsoft.WindowsServerSolutions.Setup.SBSSetup.ProgressPagePresenter._RunTasks(Object sender, DoWorkEventArgs e) at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument) --- End of inner exception stack trace --- at Microsoft.WindowsServerSolutions.Setup.SBSSetup.ProgressPagePresenter.TasksCompleted(Object sender, RunWorkerCompletedEventArgs e) --- End of inner exception stack trace --- at System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbacks() at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at Microsoft.WindowsServerSolutions.Common.Wizards.Framework.WizardChainEngine.Launch() at Microsoft.WindowsServerSolutions.Setup.SBSSetup.MainClass._LaunchWizard() at Microsoft.WindowsServerSolutions.Setup.SBSSetup.MainClass.RealMain(String[] args) at Microsoft.WindowsServerSolutions.Setup.SBSSetup.MainClass.Main(String[] args) [4956] 121016.225455.0865: Setup: Removed the password. [4956] 121016.225455.0905: Setup: Deleting scheduled task at path Microsoft\Windows\Windows Small Business Server 2011 Standard with name Setup [4956] 121016.225455.8055: Setup: Removed SBSSetup from the RunOnce.

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  • What can I do to prevent system power downs?

    - by Joe King
    Yesterday I was given my brother's old laptop - core i7, 2.67GHz, 8GB RAM, 128GB SSD, Win7 64 bit. It's a Sony Vaio Z11. Approx 18 months old. When running something computationally intensive, the fan starts up and after about 30 secs it just powers itself down with no warning. I guess it is overheating. There is nothing in the event logs to suggest what is causing it - the only thing I see is "the last system shutdown was unexpected" or something similar. This is a problem for me because I use a lot of number crunching apps, which pretty much makes it useless to me. I would like to know if there is anything I can do, other than the obvious things I've done already - open up and clean out dust, re-install the OS. According to my brother, this problem started about 6 months ago when it was already outside warranty. If it's just used for simple things - web browsing, word processing etc, the problem does not occur. Any ideas for what I can do to fix this ? Update: I found that the laptop has 2 hardware settings for graphics: Speed and Stamina - the Speed setting seems to use an nvidia GEforce GT 330M, while the Stamina setting uses an Intel chipset. With the setting on Speed, I can hear the fan the whole time, and the system powers down after a short while (5-10 mins) even just doing basic tasks (browsing this site for example), but doesn't shut down if I just leave it switched on. In this mode it also sometimes just freezes the screen and I have to power off myself. However on Stamina setting it only powers down when doing number crunching and never freezes the screen.

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  • how can I design a good architechture for a Transaction Processing System?

    - by ghedas
    I have a project that must design an architecture for it. This project is a something like a Transaction Processing system and I need to know something like this: when and where I must use synchronous and asynchronous relations between its components? If always I use synchronous relations, the amount of messages maybe become exceeded and makes problem for TP system, and on the other hand synchronous relations make lots of delay, I think a mixture of them is required! If other parameters required to considering please help me! the most nonfunctional requirements of this project are performance and availability of it. I need useful materials and suggestions for it.

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