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• Clean MVC design when there is viewer latency

  - by Tony Suffolk 66

  It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane implements how the game is displayed, and user iteraction - i.e. what game items or controls the user has activated. The challenge that I have is this : In my game the Control Plane can move game items more or less instaneously (The decision about what item to place where - and some of the initial consequences of that placement are reasonably trivial to calculate), but I want to design the Control Plane so that the View plane can display these movements either instaneously or using movement animations. The other complication is that player interaction must be locked out while those game items are moving (similar to chess - you can't attack an opposing piece as it moves past one of your pieces) So do I : Implement all the logic in the Control Plane asynchronously - and separate the descision making from the actions - so the Control plane decides piece 'A' needs to move to a given place - tells the view plane, and but does not implement the move in data until the view plane informs the control plane that the move/animation is complete. A lot of interlock points between the two layers. Implement all the control plane logic in one place - decisions and movement (keeping track of what moved where), and pass all the movements in one go to the View plane to do with what it will. Control Plane is almost fire and forget here. A hybrid of 1 & 2 - The control plane implements all the moves in a temporary data store - but maintains a second store which reflects what is actually visible to the viewer, based on calls and feedback from the View plane. All 3 are relatively easy to implement (target language is python), but having never done a clean MVC pattern with view latency before - I am not sure which design is best

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• What is the simplest human readable configuration file format?

  - by Juha

  Current configuration file is as follows: mainwindow.title = 'test' mainwindow.position.x = 100 mainwindow.position.y = 200 mainwindow.button.label = 'apply' mainwindow.button.size.x = 100 mainwindow.button.size.y = 30 logger.datarate = 100 logger.enable = True logger.filename = './test.log' This is read with python to a nested dictionary: { 'mainwindow':{ 'button':{ 'label': {'value':'apply'}, ... }, 'logger':{ datarate: {'value': 100}, enable: {'value': True}, filename: {'value': './test.log'} }, ... } Is there a better way of doing this? The idea is to get XML type of behavior and avoid XML as long as possible. The end user is assumed almost totally computer illiterate and basically uses notepad and copy-paste. Thus the python standard "header + variables" type is considered too difficult. The dummy user edits the config file, able programmers handle the dictionaries. Nested dictionary is chosen for easy splitting (logger does not need or even cannot have/edit mainwindow parameters).

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• Is there a Design Pattern for preventing dangling references?

  - by iFreilicht

  I was thinking about a design for custom handles. The thought is to prevent clients from copying around large objects. Now a regular handle class would probably suffice for that, but it doesn't solve the "dangling reference problem"; If a client has multiple handles of the same object and deletes the object via one of them, all the others would be invalid, but not know it, so the client could write or read parts of the memory he shouldn't have access to. Is there a design pattern to prevent this from happening? Two ideas: An observer-like pattern where the destructor of an object would notify all handles. "Handle handles" (does such a thing even exist?). All the handles don't really point to the object, but to another handle. When the object gets destroyed, this "master-handle" invalidates itself and therefore all that point to it.

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• How to manage long running background threads and report progress with DDD

  - by Mr Happy

  Title says most of it. I have found surprising little information about this. I have a long running operation of which the user wants to see the progress (as in, item x of y processed). I also need to be able to pause and stop the operation. (Stopping doesn't rollback the items already processed.) The thing is, it's not that each item takes a long time to get processed, it's that that there are usually a lot of items. And what I've read about so far is that it's somewhat of an anti-pattern to put something like a queue in the DB. I currently don't have any messaging system in place, and I've never worked with one either. Another thing I read somewhere is that progress reporting is something that belongs in the application layer, but it didn't go into the details. So having said all this, what I have in mind is the following. User request with list of items enters the application layer. Application layer gets some information from the domain needed to process the items. Application layer passes the items and the information off to some domain service (should the implementation of this service belong in the infrastructure layer?) This service spins up a worker thread with callbacks for both progress reporting and pausing/stopping it. This worker thread will process each item in it's own UoW. This means the domain information from earlier needs to be stored in some DTO. Since nothing is really persisted, the service should be singleton and thread safe Whenever a user requests a progress report or wants to pause/stop the operation, the application layer will ask the service. Would this be a correct solution? Or am I at least on the right track with this? Especially the singleton and thread safe part makes the whole thing feel icky.

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• Algorithm to Solve Most of a Problem

  - by Mike G

  I need an Algorithm/Design Pattern that allows me to try to get the maximum number of rules followed. So I have a couple teams and I need to pair them with a referee and against each other into a round robin. There a rules on who can compete with who and who can judge who so I need to find the configuration that satisfies the most of these. Some rules are more important than others and are "worth more" when evaluating "what satisfies the most of them" There probably isn't a algorithm for this, but is there a design pattern that could help me maximize my chances of finding this configuration?

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• How to have operations with character/items in binary with concrete operations?

  - by Piperoman

  I have the next problem. A item can have a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can have some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have tried to set binary flags to states, and use AND to combine different states, checking before if it is possible or not to do it, or change to another status. Does there exist a concrete approach to solve this problem efficiently without having an interminable switch that checks every state with every new state? It is relatively easy to check 2 different states, but if there exists a third state it is not trivial to do.

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• How can I selectively update XNA GameComponents?

  - by Bill

  I have a small 2D game I'm working on in XNA. So far, I have a player-controlled ship that operates on vector thrust and is terribly fun to spin around in circles. I've implemented this as a DrawableGameComponent and registered it with the game using game.Components.Add(this) in the Ship object constructor. How can I implement features like pausing and a menu system with my current implementation? Is it possible to set certain GameComponents to not update? Is this something for which I should even be using a DrawableGameComponent? If not, what are more appropriate uses for this?

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• Relationship DAO, Servlet, JSP and POJO

  - by John Hendrik

  I want to implement a JSP, POJO, DAO and Servlet in my J2EE program. However, I don't fully understand how the relationship between these elements should be. Is the following (MVC) setup the right way to do it? Main class creates servlet(controller) Servlet has a DAO defined in its class DAO has a POJO defined in its class Servlet communicates with the view (JSP page) Please give your feedback.

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• Recommened design pattern to handle multiple compression algorithms for a class hierarchy

  - by sgorozco

  For all you OOD experts. What would be the recommended way to model the following scenario? I have a certain class hierarchy similar to the following one: class Base { ... } class Derived1 : Base { ... } class Derived2 : Base { ... } ... Next, I would like to implement different compression/decompression engines for this hierarchy. (I already have code for several strategies that best handle different cases, like file compression, network stream compression, legacy system compression, etc.) I would like the compression strategy to be pluggable and chosen at runtime, however I'm not sure how to handle the class hierarchy. Currently I have a tighly-coupled design that looks like this: interface ICompressor { byte[] Compress(Base instance); } class Strategy1Compressor : ICompressor { byte[] Compress(Base instance) { // Common compression guts for Base class ... // if( instance is Derived1 ) { // Compression guts for Derived1 class } if( instance is Derived2 ) { // Compression guts for Derived2 class } // Additional compression logic to handle other class derivations ... } } As it is, whenever I add a new derived class inheriting from Base, I would have to modify all compression strategies to take into account this new class. Is there a design pattern that allows me to decouple this, and allow me to easily introduce more classes to the Base hierarchy and/or additional compression strategies?

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• Identifying the best pattern

  - by Daniel Grillo

  I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern.

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• Best Creational Pattern for loggers in a multi-threaded system?

  - by Dipan Mehta

  This is a follow up question on my past questions : Concurrency pattern of logger in multithreaded application As suggested by others, I am putting this question separately. As the learning from the last question. In a multi-threaded environment, the logger should be made thread safe and probably asynchronous (where in messages are queued while a background thread does writing releasing the requesting object thread). The logger could be signleton or it can be a per-group logger which is a generalization of the above. Now, the question that arise is how does logger should be assigned to the object? There are two options I can think of: 1. Object requesting for the logger: Should each of the object call some global API such as get_logger()? Such an API returns "the" singleton or the group logger. However, I feel this involves assumption about the Application environment to implement the logger -which I think is some kind of coupling. If the same object needs to be used by other application - this new application also need to implement such a method. 2. Assign logger through some known API The other alternative approach is to create a kind of virtual class which is implemented by application based on App's own structure and assign the object sometime in the constructor. This is more generalized method. Unfortunately, when there are so many objects - and rather a tree of objects passing on the logger objects to each level is quite messy. My question is there a better way to do this? If you need to pick any one of the above, which approach is would you pick and why? Other questions remain open about how to configure them: How do objects' names or ID are assigned so that will be used for printing on the log messages (as the module names) How do these objects find the appropriate properties (such as log levels, and other such parameters) In the first approach, the central API needs to deal with all this varieties. In the second approach - there needs to be additional work. Hence, I want to understand from the real experience of people, as to how to write logger effectively in such an environment.

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• Pattern for a class that does only one thing

  - by Heinzi

  Let's say I have a procedure that does stuff: void doStuff(initalParams) { ... } Now I discover that "doing stuff" is quite a compex operation. The procedure becomes large, I split it up into multiple smaller procedures and soon I realize that having some kind of state would be useful while doing stuff, so that I need to pass less parameters between the small procedures. So, I factor it out into its own class: class StuffDoer { private someInternalState; public Start(initalParams) { ... } // some private helper procedures here ... } And then I call it like this: new StuffDoer().Start(initialParams); or like this: new StuffDoer(initialParams).Start(); And this is what feels wrong. When using the .NET or Java API, I always never call new SomeApiClass().Start(...);, which makes me suspect that I'm doing it wrong. Sure, I could make StuffDoer's constructor private and add a static helper method: public static DoStuff(initalParams) { new StuffDoer().Start(initialParams); } But then I'd have a class whose external interface consists of only one static method, which also feels weird. Hence my question: Is there a well-established pattern for this type of classes that have only one entry point and have no "externally recognizable" state, i.e., instance state is only required during execution of that one entry point?

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• Is there a name for the Builder Pattern where the Builder is implemented via interfaces so certain parameters are required?

  - by Zipper

  So we implemented the builder pattern for most of our domain to help in understandability of what actually being passed to a constructor, and for the normal advantages that a builder gives. The one twist was that we exposed the builder through interfaces so we could chain required functions and unrequired functions to make sure that the correct parameters were passed. I was curious if there was an existing pattern like this. Example below: public class Foo { private int someThing; private int someThing2; private DateTime someThing3; private Foo(Builder builder) { this.someThing = builder.someThing; this.someThing2 = builder.someThing2; this.someThing3 = builder.someThing3; } public static RequiredSomething getBuilder() { return new Builder(); } public interface RequiredSomething { public RequiredDateTime withSomething (int value); } public interface RequiredDateTime { public OptionalParamters withDateTime (DateTime value); } public interface OptionalParamters { public OptionalParamters withSeomthing2 (int value); public Foo Build ();} public static class Builder implements RequiredSomething, RequiredDateTime, OptionalParamters { private int someThing; private int someThing2; private DateTime someThing3; public RequiredDateTime withSomething (int value) {someThing = value; return this;} public OptionalParamters withDateTime (int value) {someThing = value; return this;} public OptionalParamters withSeomthing2 (int value) {someThing = value; return this;} public Foo build(){return new Foo(this);} } } Example of how it's called: Foo foo = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).build(); Foo foo2 = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).withSomething2(3).build();

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• How to play many sounds at once in OpenAL

  - by Krom

  Hello, I'm developing an RTS game and I would like to add sounds to it. My choice has landed on OpenAL. I have plenty of units which from time to time make sounds: fSound.Play(sfx_shoot, location). Sounds often repeat, e.g. when squad of archers shoots arrows, but they are not synced with each other. My questions are: What is the common design pattern to play multiple sounds in OpenAL, when some of them are duplicate? What are the hardware limitations on sounds count and tricks to overcome them?

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• Resources about cross platform application development in ANSI C [closed]

  - by Anindya Chatterjee

  Where can I get good resources for learning cross platform application development in plain ISO/ANSI C? I have cygwin and eclipse cdt with me to start in my win7 pc. I just need a couple of good resources containing all the best practices and techniques to write good and robust and scalable cross platform application. I am totally new to this cross platform business, no prior idea. Want to learn it in a proper way from the very beginning. Please help me out here.

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• Why is nesting or piggybacking errors within errors bad in general?

  - by dietbuddha

  Why is nesting or piggybacking errors within errors bad in general? To me it seems bad intuitively, but I'm suspicious in that I cannot adequately articulate why it is bad. This may be because it is not in general bad and that it is only bad in specific instances. Why is it detrimental to design error/exception handling in such a way. The specific instance is that of a REST service. There is a desire by some to use http errors (specifically the 500 response) as a way to indicate any problem with specific instances of a resource. An example of an instance resource in this case would be: http://server/ticket/80 # instance http://server/ticket # not an instance So this is the behavior that is being proposed. If ticket 80 does not exist return a http response code of 500. Within the body of the error return the "real" error as an additional error code and description. If the ticket resource doesn't exist return a response code of 404.

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• Relative encapsulation design

  - by taher1992

  Let's say I am doing a 2D application with the following design: There is the Level object that manages the world, and there are world objects which are entities inside the Level object. A world object has a location and velocity, as well as size and a texture. However, a world object only exposes get properties. The set properties are private (or protected) and are only available to inherited classes. But of course, Level is responsible for these world objects, and must somehow be able to manipulate at least some of its private setters. But as of now, Level has no access, meaning world objects must change its private setters to public (violating encapsulation). How to tackle this problem? Should I just make everything public? Currently what I'm doing is having a inner class inside game object that does the set work. So when Level needs to update an objects location it goes something like this: void ChangeObject(GameObject targetObject, int newX, int newY){ // targetObject.SetX and targetObject.SetY cannot be set directly var setter = new GameObject.Setter(targetObject); setter.SetX(newX); setter.SetY(newY); } This code feels like overkill, but it doesn't feel right to have everything public so that anything can change an objects location for example.

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• Design for object with optional and modifiable attributtes?

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• Are there any concerns with using a static read-only unit of work so that it behaves like a cache?

  - by Rowan Freeman

  Related question: How do I cache data that rarely changes? I'm making an ASP.NET MVC4 application. On every request the security details about the user will need to be checked with the area/controller/action that they are accessing to see if they are allowed to view it. The security information is stored in the database. For example: User Permission UserPermission Action ActionPermission A "Permission" is a token that is applied to an MVC action to indicate that the token is required in order to access the action. Once a user is given the permission (via the UserPermission table) then they have the token and can therefore access the action. I've been looking in to how to cache this data (since it rarely changes) so that I'm only querying in-memory data and not hitting a database (which is a considerable performance hit at the moment). I've tried storing things in lists, using a caching provider but I either run in to problems or performance doesn't improve. One problem that I constantly run in to is that I'm using lazy loading and dynamic proxies with EntityFramework. This means that even if I ToList() everything and store them somewhere static, the relationships are never populated. For example, User.Permissions is an ICollection but it's always null. I don't want to Include() everything because I'm trying to keep things simple and generic (and easy to modify). One thing I know is that an EntityFramework DbContext is a unit of work that acts with 1st-level caching. That is, for the duration of the unit of work, everything that is accessed is cached in memory. I want to create a read-only DbContext that will exist indefinitely and will only be used to read about permission data. Upon testing this it worked perfectly; my page load times went from 200ms+ to 20ms. I can easily force the data to refresh at certain intervals or simply leave it to refresh when the application pool is recycled. Basically it will behave like a cache. Note that the rest of the application will interact with other contexts that exist per request as normal. Is there any disadvantage to this approach? Could I be doing something different?

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• Making Modular, Reusable and Loosely Coupled MVC Components

  - by Dusan

  I am building MVC3 application and need some general guidelines on how to manage complex client side interaction between my components. Here is my definition of one component in general way: Component which has it's own controller, model and view. All of the component's logic is placed inside these three parts and component is sort of "standalone", it contains it's own form, data needed for interaction, updates itself with Ajax and so on. Beside this internal logic and behavior of the component, it needs to be able to "Talk" to the outside world. By this I mean it should provide data and events (sort of) so when this component gets embedded in pages can notify other components which then can update based on the current state and data. I have an idea to use client ViewModel (in java-script) which would hookup all relevant components on page and control interaction between them. This would make components reusable, modular - independent of the context in which they are used. How would you do this, I am a bit stuck as I do not know if this is a good approach and there is a technical possibility to achieve this using java-script/jquery. The confusing part is about update via Ajax, how to ensure that component is properly linked to ViewModel when component is Ajax updated (or even worse removed or dynamically added). Also, how should this ViewModel be constructed and which technicalities to use here and in components to work as synergy??? On the web, I have found the various examples of the similar approach, but they are oversimplified (even for dummies) or over specific and do not provide valuable resource or general solution for this kind of implementation. If you have some serious examples it would be, also, very helpful. Note: My aim is to make interactions between many components on the same page simpler and more robust and elegant.

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• Is it better to define all routes in the Global.asax than to define separately in the areas?

  - by Matthew Patrick Cashatt

  I am working on a MVC 4 project that will serve as an API layer of a larger application. The developers that came before me set up separate Areas to separate different API requests (i.e Search, Customers, Products, and so forth). I am noticing that each Area has separate Area registration classes that define routes for that area. However, the routes defined are not area-specific (i.e. {controller}/{action}/{id} might be defined redundantly in a couple of areas). My instinct would be to move all of these route definitions to a common place like the Global.asax to avoid redundancy and collisions, but I am not sure if I am correct about that.

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• What are DRY, KISS, SOLID, etc. classified as?

  - by Morgan Herlocker

  Is something like DRY a design pattern, a methodology, or something in between? They do not have specific implementations that could neccessarily be demonstrated(even if you can easily demonstrate a case NOT using something like KISS... see The Daily WTF for a plethora of examples), nor do they fully explain a development process like a methodology generally would. Where does that leave these types of "rule of thumb"'s?

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• Augmenting functionality of subclasses without code duplication in C++

  - by Rob W

  I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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• Implementing a ILogger interface to log data

  - by Jon

  I have a need to write data to file in one of my classes. Obviously I will pass an interface into my class to decouple it. I was thinking this interface will be used for testing and also in other projects. This is my interface: //This could be used by filesystem, webservice public interface ILogger { List<string> PreviousLogRecords {get;set;} void Log(string Data); } public interface IFileLogger : ILogger { string FilePath; bool ValidFileName; } public class MyClassUnderTest { public MyClassUnderTest(IFileLogger logger) {....} } [Test] public void TestLogger() { var mock = new Mock<IFileLogger>(); mock.Setup(x => x.Log(Is.Any<string>).AddsDataToList()); //Is this possible?? var myClass = new MyClassUnderTest(mock.Object); myClass.DoSomethingThatWillSplitThisAndLog3Times("1,2,3"); Assert.AreEqual(3,mock.PreviousLogRecords.Count); } This won't work I don't believe as nothing is storing the items so is this possible using Moq and also what do you think of the design of the interface?

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