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  • LI .Net User Group June 3rd, 2010 Meeting with Sam Abraham

    - by Sam Abraham
    It was a pleasure seeing old friends and meeting new ones at the LI .Net User Group Meeting on Thursday June 3rd 2010. I was very impressed as more than 35 developers were present which highlights the buzz MVC is creating with its latest release. We covered an introduction to MVC then went on to discuss new features in MVC2. I enjoyed the good dialogue among the group as we discussed how MVC can fit side-by-side with an existing WebForms paradigm and how MVC Support for TDD can dramatically shift Architecture practices as we know them. Looking forward to meeting you all next time I am on the Island. Below are some photos of the event. --Sam Abraham Site Director - West Palm Beach .Net User Group

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  • Playing NSF music in FMOD.net

    - by Tesserex
    So, as the title says, I want to be able to play NSF files using FMOD, because my project already uses FMOD and I'd rather not replace it. This will involve figuring out how existing players and emulators work and porting it. I haven't yet found an existing player that uses FMOD. My starting point is the MyNes source from http://sourceforge.net/projects/mynes/. There are two big steps between here and what I'm looking for. MyNes plays from a ROM, not NSF. So, I have to rip out the APU and get it to play NSF files. The MyNes APU uses SlimDX, so I have to convert that to FMOD.NET. I am really stuck about how to go about either of these, because I'm not that familiar with audio formats and it's hard finding resources online. So here are a few questions: From what I can tell from the NSF spec at http://kevtris.org/nes/nsfspec.txt, it's just contains the relevant memory section of the ROM, plus the header. If anyone can verify or correct this that would be great. The emulator APU uses data from the rest of the emulator to play, including things like cycle counts. I'm not sure what replaces this in a standalone player. Can't I just load all the music data at once into a stream and play it? Joining #1 and #2, does the header data from the NSF substitute for some of the ROM data in the emulator code? Using FMOD, will I be following the usercreatedsound example for loading a stream? And does this format count as PCM? Specifically MyNes says PCM8. Any tips on loading / playing the stream in FMOD are appreciated. As an aside, I don't really understand the loading / playing sections of the spec I linked at all. It seems to apply to 6502 systems / emulators only and not to my situation. I know it's a long shot for anyone here to have enough experience in this area to help, but anything you can provide is definitely appreciated. A link to an existing .NET library that does this would be even better, but I don't believe one exists.

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  • Location, Orientation, and Writing a Custom Control with Mono for Android, .NET, and C#

    - by Wallym
    Like real estate, mobile is about location, location, location. That means that direction is an important item. And just as important is how this information is presented to the user. In Nov. 2011, we talked about building a user interface in Mono For Android. In this article, I'll expand a little bit on that by creating a compass that displays north. We'll use Android's built-in sensor support to determine the orientation of the device, then use a custom control to display North. The output will look like

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  • HEALTH MONITORING IN ASP.NET 3.5

    - by kaleidoscope
    Health monitoring gives you the option of monitoring your application once you have developed and deployed your application. The Health Monitoring system works by recording event information to a specified log source. Health monitoring can be attained by doing adding a few configurations in web.config file. Health Monitoring is split into 5 categories: *EventMappings *BufferModes *Rules *Providers *Profiles. Find the below links for details: http://www.dotnetbips.com/articles/63431cdd-07a2-434f-9681-7ef5c2cf0548.aspx http://msdn.microsoft.com/en-us/library/ms178703(VS.80).aspx   Ranjit, M

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  • Custom Model Binding of IEnumerable Properties in ASP.Net MVC 2

    - by Doug Lampe
    MVC 2 provides a GREAT feature for dealing with enumerable types.  Let's say you have an object with a parent/child relationship and you want to allow users to modify multiple children at the same time.  You can simply use the following syntax for any indexed enumerables (arrays, generic lists, etc.) and then your values will bind to your enumerable model properties. 1: <% using (Html.BeginForm("TestModelParameter", "Home")) 2: { %> 3: < table > 4: < tr >< th >ID</th><th>Name</th><th>Description</th></tr> 5: <% for (int i = 0; i < Model.Items.Count; i++) 6: { %> 7: < tr > 8: < td > 9: <%= i %> 10: </ td > 11: < td > 12: <%= Html.TextBoxFor(m => m.Items[i].Name) %> 13: </ td > 14: < td > 15: <%= Model.Items[i].Description %> 16: </ td > 17: </ tr > 18: <% } %> 19: </ table > 20: < input type ="submit" /> 21: <% } %> Then just update your model either by passing it into your action method as a parameter or explicitly with UpdateModel/TryUpdateModel. 1: public ActionResult TestTryUpdate() 2: { 3: ContainerModel model = new ContainerModel(); 4: TryUpdateModel(model); 5:   6: return View("Test", model); 7: } 8:   9: public ActionResult TestModelParameter(ContainerModel model) 10: { 11: return View("Test", model); 12: } Simple right?  Well, not quite.  The problem is the DefaultModelBinder and how it sets properties.  In this case our model has a property that is a generic list (Items).  The first bad thing the model binder does is create a new instance of the list.  This can be fixed by making the property truly read-only by removing the set accessor.  However this won't help because this behaviour continues.  As the model binder iterates through the items to "set" their values, it creates new instances of them as well.  This means you lose any information not passed via the UI to your controller so in the examplel above the "Description" property would be blank for each item after the form posts. One solution for this is custom model binding.  I have put together a solution which allows you to retain the structure of your model.  Model binding is a somewhat advanced concept so you may need to do some additional research to really understand what is going on here, but the code is fairly simple.  First we will create a binder for the parent object which will retain the state of the parent as well as some information on which children have already been bound. 1: public class ContainerModelBinder : DefaultModelBinder 2: { 3: /// <summary> 4: /// Gets an instance of the model to be used to bind child objects. 5: /// </summary> 6: public ContainerModel Model { get; private set; } 7:   8: /// <summary> 9: /// Gets a list which will be used to track which items have been bound. 10: /// </summary> 11: public List<ItemModel> BoundItems { get; private set; } 12:   13: public ContainerModelBinder() 14: { 15: BoundItems = new List<ItemModel>(); 16: } 17:   18: protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) 19: { 20: // Set the Model property so child binders can find children. 21: Model = base.CreateModel(controllerContext, bindingContext, modelType) as ContainerModel; 22:   23: return Model; 24: } 25: } Next we will create the child binder and have it point to the parent binder to get instances of the child objects.  Note that this only works if there is only one property of type ItemModel in the parent class since the property to find the item in the parent is hard coded. 1: public class ItemModelBinder : DefaultModelBinder 2: { 3: /// <summary> 4: /// Gets the parent binder so we can find objects in the parent's collection 5: /// </summary> 6: public ContainerModelBinder ParentBinder { get; private set; } 7: 8: public ItemModelBinder(ContainerModelBinder containerModelBinder) 9: { 10: ParentBinder = containerModelBinder; 11: } 12:   13: protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) 14: { 15: // Find the item in the parent collection and add it to the bound items list. 16: ItemModel item = ParentBinder.Model.Items.FirstOrDefault(i => !ParentBinder.BoundItems.Contains(i)); 17: ParentBinder.BoundItems.Add(item); 18: 19: return item; 20: } 21: } Finally, we will register these binders in Global.asax.cs so they will be used to bind the classes. 1: protected void Application_Start() 2: { 3: AreaRegistration.RegisterAllAreas(); 4:   5: ContainerModelBinder containerModelBinder = new ContainerModelBinder(); 6: ModelBinders.Binders.Add(typeof(ContainerModel), containerModelBinder); 7: ModelBinders.Binders.Add(typeof(ItemModel), new ItemModelBinder(containerModelBinder)); 8:   9: RegisterRoutes(RouteTable.Routes); 10: } I'm sure some of my fellow geeks will comment that this could be done more efficiently by simply rewriting some of the methods of the default model binder to get the same desired behavior.  I like my method shown here because it extends the binder class instead of modifying it so it minimizes the potential for unforseen problems. In a future post (if I ever get around to it) I will explore creating a generic version of these binders.

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  • Playing NSF music in FMOD.net

    - by Tesserex
    So, as the title says, I want to be able to play NSF files using FMOD, because my project already uses FMOD and I'd rather not replace it. This will involve figuring out how existing players and emulators work and porting it. I haven't yet found an existing player that uses FMOD. My starting point is the MyNes source from http://sourceforge.net/projects/mynes/. There are two big steps between here and what I'm looking for. MyNes plays from a ROM, not NSF. So, I have to rip out the APU and get it to play NSF files. The MyNes APU uses SlimDX, so I have to convert that to FMOD.NET. I am really stuck about how to go about either of these, because I'm not that familiar with audio formats and it's hard finding resources online. So here are a few questions: From what I can tell from the NSF spec at http://kevtris.org/nes/nsfspec.txt, it's just contains the relevant memory section of the ROM, plus the header. If anyone can verify or correct this that would be great. The emulator APU uses data from the rest of the emulator to play, including things like cycle counts. I'm not sure what replaces this in a standalone player. Can't I just load all the music data at once into a stream and play it? Joining #1 and #2, does the header data from the NSF substitute for some of the ROM data in the emulator code? Using FMOD, will I be following the usercreatedsound example for loading a stream? And does this format count as PCM? Specifically MyNes says PCM8. Any tips on loading / playing the stream in FMOD are appreciated. As an aside, I don't really understand the loading / playing sections of the spec I linked at all. It seems to apply to 6502 systems / emulators only and not to my situation. I know it's a long shot for anyone here to have enough experience in this area to help, but anything you can provide is definitely appreciated. A link to an existing .NET library that does this would be even better, but I don't believe one exists.

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  • BDD using SpecFlow on ASP.NET MVC Application

    - by Rajesh Pillai
    I usually love doing TDD and am moving towards understanding BDD (Behaviour Driven Development).  My learnings are documented in the form of an article at CodeProject. The URL is http://www.codeproject.com/KB/architecture/BddWithSpecFlow.aspx I will keep this updated as and when I learn a couple of more things. Hope you like it. Cheers !!!

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  • CodePlex Daily Summary for Wednesday, August 06, 2014

    CodePlex Daily Summary for Wednesday, August 06, 2014Popular ReleasesRecaptcha for .NET: Recaptcha for .NET v1.6.0: What's New?Bug fixes Optimized codeMath.NET Numerics: Math.NET Numerics v3.2.0: Linear Algebra: Vector.Map2 (map2 in F#), storage-optimized Linear Algebra: fix RemoveColumn/Row early index bound check (was not strict enough) Statistics: Entropy ~Jeff Mastry Interpolation: use Array.BinarySearch instead of local implementation ~Candy Chiu Resources: fix a corrupted exception message string Portable Build: support .Net 4.0 as well by using profile 328 instead of 344. .Net 3.5: F# extensions now support .Net 3.5 as well .Net 3.5: NuGet package now contains pro...Lib.Web.Mvc & Yet another developer blog: Lib.Web.Mvc 6.4.2: Lib.Web.Mvc is a library which contains some helper classes for ASP.NET MVC such as strongly typed jqGrid helper, XSL transformation HtmlHelper/ActionResult, FileResult with range request support, custom attributes and more. Release contains: Lib.Web.Mvc.dll with xml documentation file Standalone documentation in chm file and change log Library source code Sample application for strongly typed jqGrid helper is available here. Sample application for XSL transformation HtmlHelper/ActionRe...Virto Commerce Enterprise Open Source eCommerce Platform (asp.net mvc): Virto Commerce 1.11: Virto Commerce Community Edition version 1.11. To install the SDK package, please refer to SDK getting started documentation To configure source code package, please refer to Source code getting started documentation This release includes many bug fixes and minor improvements. More details about this release can be found on our blog at http://blog.virtocommerce.com.Json.NET: Json.NET 6.0 Release 4: New feature - Added Merge to LINQ to JSON New feature - Added JValue.CreateNull and JValue.CreateUndefined New feature - Added Windows Phone 8.1 support to .NET 4.0 portable assembly New feature - Added OverrideCreator to JsonObjectContract New feature - Added support for overriding the creation of interfaces and abstract types New feature - Added support for reading UUID BSON binary values as a Guid New feature - Added MetadataPropertyHandling.Ignore New feature - Improv...VidCoder: 1.5.24 Beta: Added NL-Means denoiser. Updated HandBrake core to SVN 6254. Added extra error handling to DVD player code to avoid a crash when the player was moved.PowerShell App Deployment Toolkit: PowerShell App Deployment Toolkit v3.1.5: *Added Send-Keys function to send a sequence of keys to an application window (Thanks to mmashwani) *Added 3 optimization/stability improvements to Execute-Process following MS best practice (Thanks to mmashwani) *Fixed issue where Execute-MSI did not use value from XML file for uninstall but instead ran all uninstalls silently by default *Fixed error on 1641 exit code (should be a success like 3010) *Fixed issue with error handling in Invoke-SCCMTask *Fixed issue with deferral dates where th...AutoUpdater.NET : Auto update library for VB.NET and C# Developer: AutoUpdater.NET 1.3: Fixed problem in DownloadUpdateDialog where download continues even if you close the dialog. Added support for new url field for 64 bit application setup. AutoUpdater.NET will decide which download url to use by looking at the value of IntPtr.Size. Added German translation provided by Rene Kannegiesser. Now developer can handle update logic herself using event suggested by ricorx7. Added italian translation provided by Gianluca Mariani. Fixed bug that prevents Application from exiti...SEToolbox: SEToolbox 01.041.012 Release 1: Added voxel material textures to read in with mods. Fixed missing texture replacements for mods. Fixed rounding issue in raytrace code. Fixed repair issue with corrupt checkpoint file. Fixed issue with updated SE binaries 01.041.012 using new container configuration.Magick.NET: Magick.NET 6.8.9.601: Magick.NET linked with ImageMagick 6.8.9.6 Breaking changes: - Changed arguments for the Map method of MagickImage. - QuantizeSettings uses Riemersma by default.Version Control Guide (ex-Branching & Merging): v3.0 - Visual Studio 2013 (Spanish): Important: This download has been created using ALM Ranger bits by the community, for the community. Although ALM Rangers were involved in the process, the content has not been through their quality review. Please post your candid feedback and improvement suggestions to the Community tab of this Codeplex project. Translated by: Juan María Laó Ramos See ¿Habla Español? … Testing Unitario con Microsoft® Fakes http://blogs.msdn.com/b/willy-peter_schaub/archive/2013/08/22/191-habla-espa-241-ol...Windows forms generator: Windows forms generator beta 2: Second beta release of windows forms generator. Have some basic configuration and can handle basic types. Supported types: int string double float long decimal short bool List<E> Vector2 (Microsoft.Xna.Framework, new in beta 2) Fixed bugs in beta 2: Problem with nested classes and list Known bugs: Form height sometimes get weird (fix it by using form attribute on class) Can't create a form with just a listSharePoint Real Time Log Viewer: SharePoint Real Time Log Viewer - Source: Source codeModern Audio Tagger: Modern Audio Tagger 1.0.0.0: Modern Audio Tagger is bornQuickMon: Version 3.20: Added a 'Directory Services Query' collector agent. This collector allows for querying Active Directory using simple DirectorySearcher queries. Note: The current implementation only supports 'LDAP://' related path queries. In a future release support for other 'Providers' will be added as well.Grunndatakvalitet: Initial working: Show Altinn metadata in Excel. To get a live list you need to run the sql script on a server and update the connection string in ExcelMultiple Threads TCP Server: Project: this Project is based on VS 2013, .net freamwork 4.0, you can open it by vs 2010 or laterAricie Shared: Aricie.Shared Version 1.8.00: Version 1.8.0 - Release Notes New: Expression Builder to design Flee Expressions New: Cryptographic helpers and configuration classes Improvement: Many fixes and improvements with property editor Improvement: Token Replace Property explorer now has a restricted mode for additional security Improvement: Better variables, types and object manipulation Fixed: smart file and flee bugs Fixed: Removed Exception while trying to read unsuported files Improvement: several performance twe...DbEntry.Net (Leafing Framework): DbEntry.Net 4.2: DbEntry.Net is a lightweight Object Relational Mapping (ORM) database access compnent for .Net 4.0+. It has clearly and easily programing interface for ORM and sql directly, and supoorted Access, Sql Server, MySql, SQLite, Firebird, PostgreSQL and Oracle. It also provide a Ruby On Rails style MVC framework. Asp.Net DataSource and a simple IoC. DbEntry.Net.v4.2.Setup.zip include the setup package. DbEntry.Net.v4.2.Src.zip include source files and unit tests. DbEntry.Net.v4.2.Samples.zip ...Drop and Create indexes SSIS Task: Assembly and Setup files: This zip contains the task assembly and setup executable's. Click here for the Installation GuideNew ProjectsDestiny of an Emperor: game cocos2d-x sanguoGameCastleVania: Game th?y dungOrchard Application Host: The Orchard Application Host is a portable environment that lets you run your application (not just web apps) inside Orchard (http://orchardproject.net).Orchard Application Host Sample: Sample project for the Orchard Application Host (https://orchardapphost.codeplex.com/).Orchard SSEO Module: Orchard Social & Search Engine Optimization ModulePhoenix Office 365 User Group Website: The Phoenix Office 365 User Group meets once per month in the Phoenix area and facilitates networking and learning around the Office 365 platform. Thingtory ( Inventory of Things ): The Thingtory Framework allows to collect data (inventory) from all kind of "things" (can be a Computer, a Phone or your Fridge ).xRM CI Framework: The xRM Continuous Integration (CI) Framework is a set of tools that makes it easy and quick to automate the builds and deployment of your CRM components.

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  • ASP.Net MVC: Areas and controllers

    - by xamlnotes
    Areas are a great feature of MVC now. The let you put common code into an Area and then its segregated from other code. That makes it really easy to put those common feature in one spot and not have the interfere with other code. So today I was working on a new area and starting to test code in it. But the controller method could not be found. Testing the routes and all of the names proved no help either. So I am banging my head against the wall. Then I took a peak at one of the existing controllers in another Area in the same app. Looked similar, but … There was a Namespaceat the top of that controller with that Area in the Namespace.  I had copied my controller in from somewhere else and therefore it did not have the Namespace there.   I put in the right Namespace and cool, it worked right away. So add that to your list when testing.

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  • ASP.NET WebAPI Security 4: Examples for various Authentication Scenarios

    - by Your DisplayName here!
    The Thinktecture.IdentityModel.Http repository includes a number of samples for the various authentication scenarios. All the clients follow a basic pattern: Acquire client credential (a single token, multiple tokens, username/password). Call Service. The service simply enumerates the claims it finds on the request and returns them to the client. I won’t show that part of the code, but rather focus on the step 1 and 2. Basic Authentication This is the most basic (pun inteneded) scenario. My library contains a class that can create the Basic Authentication header value. Simply set username and password and you are good to go. var client = new HttpClient { BaseAddress = _baseAddress }; client.DefaultRequestHeaders.Authorization = new BasicAuthenticationHeaderValue("alice", "alice"); var response = client.GetAsync("identity").Result; response.EnsureSuccessStatusCode();   SAML Authentication To integrate a Web API with an existing enterprise identity provider like ADFS, you can use SAML tokens. This is certainly not the most efficient way of calling a “lightweight service” ;) But very useful if that’s what it takes to get the job done. private static string GetIdentityToken() {     var factory = new WSTrustChannelFactory(         new WindowsWSTrustBinding(SecurityMode.Transport),         _idpEndpoint);     factory.TrustVersion = TrustVersion.WSTrust13;     var rst = new RequestSecurityToken     {         RequestType = RequestTypes.Issue,         KeyType = KeyTypes.Bearer,         AppliesTo = new EndpointAddress(Constants.Realm)     };     var token = factory.CreateChannel().Issue(rst) as GenericXmlSecurityToken;     return token.TokenXml.OuterXml; } private static Identity CallService(string saml) {     var client = new HttpClient { BaseAddress = _baseAddress };     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("SAML", saml);     var response = client.GetAsync("identity").Result;     response.EnsureSuccessStatusCode();     return response.Content.ReadAsAsync<Identity>().Result; }   SAML to SWT conversion using the Azure Access Control Service Another possible options for integrating SAML based identity providers is to use an intermediary service that allows converting the SAML token to the more compact SWT (Simple Web Token) format. This way you only need to roundtrip the SAML once and can use the SWT afterwards. The code for the conversion uses the ACS OAuth2 endpoint. The OAuth2Client class is part of my library. private static string GetServiceTokenOAuth2(string samlToken) {     var client = new OAuth2Client(_acsOAuth2Endpoint);     return client.RequestAccessTokenAssertion(         samlToken,         SecurityTokenTypes.Saml2TokenProfile11,         Constants.Realm).AccessToken; }   SWT Authentication When you have an identity provider that directly supports a (simple) web token, you can acquire the token directly without the conversion step. Thinktecture.IdentityServer e.g. supports the OAuth2 resource owner credential profile to issue SWT tokens. private static string GetIdentityToken() {     var client = new OAuth2Client(_oauth2Address);     var response = client.RequestAccessTokenUserName("bob", "abc!123", Constants.Realm);     return response.AccessToken; } private static Identity CallService(string swt) {     var client = new HttpClient { BaseAddress = _baseAddress };     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", swt);     var response = client.GetAsync("identity").Result;     response.EnsureSuccessStatusCode();     return response.Content.ReadAsAsync<Identity>().Result; }   So you can see that it’s pretty straightforward to implement various authentication scenarios using WebAPI and my authentication library. Stay tuned for more client samples!

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  • Thinktecture.IdentityModel.Http and the ASP.NET Web API CodePlex bits

    - by Your DisplayName here!
    I will keep the github repo in sync with the major releases of Web API (like Beta, RC, RTM). Because of the changes made to Web API after beta, my current bits don’t build against the CodePlex version anymore. Today I installed a build environment for the CodePlex bits, and migrated my code. It turns out the changes are pretty easy: Simply replace Request.GetUserPrincipal() with Thread.CurrentPrincipal ;) I will update the repo when RC comes out.

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  • Building the Internet of Things – with Microsoft StreamInsight and the Microsoft .Net Micro Framework

    - by Roman Schindlauer
    Fresh from the press – The March 2012 issue of MSDN Magazine features an article about the Internet of Things. It discusses in depth how you can use StreamInsight to process all the data that is continuously produced in typical Internet of Things scenarios. It also gives you an end-to-end perspective on developing Internet of Things solutions in the .NET world, ranging from the .NET Micro Framework application running on the device, the communication between the devices and the server-side all the way to powerful cross-device streaming analytics implemented in StreamInsight LINQ. You can find an online version of the article here. Happy reading! Regards, The StreamInsight Team

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  • Routing in ASP.NET4

    Routing Allows us to build friendly URL's by decoupling the URL of the HTTP Request from the physical path of the web form that serves the Request.

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  • C#/.NET Little Wonders: Constraining Generics with Where Clause

    - by James Michael Hare
    Back when I was primarily a C++ developer, I loved C++ templates.  The power of writing very reusable generic classes brought the art of programming to a brand new level.  Unfortunately, when .NET 1.0 came about, they didn’t have a template equivalent.  With .NET 2.0 however, we finally got generics, which once again let us spread our wings and program more generically in the world of .NET However, C# generics behave in some ways very differently from their C++ template cousins.  There is a handy clause, however, that helps you navigate these waters to make your generics more powerful. The Problem – C# Assumes Lowest Common Denominator In C++, you can create a template and do nearly anything syntactically possible on the template parameter, and C++ will not check if the method/fields/operations invoked are valid until you declare a realization of the type.  Let me illustrate with a C++ example: 1: // compiles fine, C++ makes no assumptions as to T 2: template <typename T> 3: class ReverseComparer 4: { 5: public: 6: int Compare(const T& lhs, const T& rhs) 7: { 8: return rhs.CompareTo(lhs); 9: } 10: }; Notice that we are invoking a method CompareTo() off of template type T.  Because we don’t know at this point what type T is, C++ makes no assumptions and there are no errors. C++ tends to take the path of not checking the template type usage until the method is actually invoked with a specific type, which differs from the behavior of C#: 1: // this will NOT compile! C# assumes lowest common denominator. 2: public class ReverseComparer<T> 3: { 4: public int Compare(T lhs, T rhs) 5: { 6: return lhs.CompareTo(rhs); 7: } 8: } So why does C# give us a compiler error even when we don’t yet know what type T is?  This is because C# took a different path in how they made generics.  Unless you specify otherwise, for the purposes of the code inside the generic method, T is basically treated like an object (notice I didn’t say T is an object). That means that any operations, fields, methods, properties, etc that you attempt to use of type T must be available at the lowest common denominator type: object.  Now, while object has the broadest applicability, it also has the fewest specific.  So how do we allow our generic type placeholder to do things more than just what object can do? Solution: Constraint the Type With Where Clause So how do we get around this in C#?  The answer is to constrain the generic type placeholder with the where clause.  Basically, the where clause allows you to specify additional constraints on what the actual type used to fill the generic type placeholder must support. You might think that narrowing the scope of a generic means a weaker generic.  In reality, though it limits the number of types that can be used with the generic, it also gives the generic more power to deal with those types.  In effect these constraints says that if the type meets the given constraint, you can perform the activities that pertain to that constraint with the generic placeholders. Constraining Generic Type to Interface or Superclass One of the handiest where clause constraints is the ability to specify the type generic type must implement a certain interface or be inherited from a certain base class. For example, you can’t call CompareTo() in our first C# generic without constraints, but if we constrain T to IComparable<T>, we can: 1: public class ReverseComparer<T> 2: where T : IComparable<T> 3: { 4: public int Compare(T lhs, T rhs) 5: { 6: return lhs.CompareTo(rhs); 7: } 8: } Now that we’ve constrained T to an implementation of IComparable<T>, this means that our variables of generic type T may now call any members specified in IComparable<T> as well.  This means that the call to CompareTo() is now legal. If you constrain your type, also, you will get compiler warnings if you attempt to use a type that doesn’t meet the constraint.  This is much better than the syntax error you would get within C++ template code itself when you used a type not supported by a C++ template. Constraining Generic Type to Only Reference Types Sometimes, you want to assign an instance of a generic type to null, but you can’t do this without constraints, because you have no guarantee that the type used to realize the generic is not a value type, where null is meaningless. Well, we can fix this by specifying the class constraint in the where clause.  By declaring that a generic type must be a class, we are saying that it is a reference type, and this allows us to assign null to instances of that type: 1: public static class ObjectExtensions 2: { 3: public static TOut Maybe<TIn, TOut>(this TIn value, Func<TIn, TOut> accessor) 4: where TOut : class 5: where TIn : class 6: { 7: return (value != null) ? accessor(value) : null; 8: } 9: } In the example above, we want to be able to access a property off of a reference, and if that reference is null, pass the null on down the line.  To do this, both the input type and the output type must be reference types (yes, nullable value types could also be considered applicable at a logical level, but there’s not a direct constraint for those). Constraining Generic Type to only Value Types Similarly to constraining a generic type to be a reference type, you can also constrain a generic type to be a value type.  To do this you use the struct constraint which specifies that the generic type must be a value type (primitive, struct, enum, etc). Consider the following method, that will convert anything that is IConvertible (int, double, string, etc) to the value type you specify, or null if the instance is null. 1: public static T? ConvertToNullable<T>(IConvertible value) 2: where T : struct 3: { 4: T? result = null; 5:  6: if (value != null) 7: { 8: result = (T)Convert.ChangeType(value, typeof(T)); 9: } 10:  11: return result; 12: } Because T was constrained to be a value type, we can use T? (System.Nullable<T>) where we could not do this if T was a reference type. Constraining Generic Type to Require Default Constructor You can also constrain a type to require existence of a default constructor.  Because by default C# doesn’t know what constructors a generic type placeholder does or does not have available, it can’t typically allow you to call one.  That said, if you give it the new() constraint, it will mean that the type used to realize the generic type must have a default (no argument) constructor. Let’s assume you have a generic adapter class that, given some mappings, will adapt an item from type TFrom to type TTo.  Because it must create a new instance of type TTo in the process, we need to specify that TTo has a default constructor: 1: // Given a set of Action<TFrom,TTo> mappings will map TFrom to TTo 2: public class Adapter<TFrom, TTo> : IEnumerable<Action<TFrom, TTo>> 3: where TTo : class, new() 4: { 5: // The list of translations from TFrom to TTo 6: public List<Action<TFrom, TTo>> Translations { get; private set; } 7:  8: // Construct with empty translation and reverse translation sets. 9: public Adapter() 10: { 11: // did this instead of auto-properties to allow simple use of initializers 12: Translations = new List<Action<TFrom, TTo>>(); 13: } 14:  15: // Add a translator to the collection, useful for initializer list 16: public void Add(Action<TFrom, TTo> translation) 17: { 18: Translations.Add(translation); 19: } 20:  21: // Add a translator that first checks a predicate to determine if the translation 22: // should be performed, then translates if the predicate returns true 23: public void Add(Predicate<TFrom> conditional, Action<TFrom, TTo> translation) 24: { 25: Translations.Add((from, to) => 26: { 27: if (conditional(from)) 28: { 29: translation(from, to); 30: } 31: }); 32: } 33:  34: // Translates an object forward from TFrom object to TTo object. 35: public TTo Adapt(TFrom sourceObject) 36: { 37: var resultObject = new TTo(); 38:  39: // Process each translation 40: Translations.ForEach(t => t(sourceObject, resultObject)); 41:  42: return resultObject; 43: } 44:  45: // Returns an enumerator that iterates through the collection. 46: public IEnumerator<Action<TFrom, TTo>> GetEnumerator() 47: { 48: return Translations.GetEnumerator(); 49: } 50:  51: // Returns an enumerator that iterates through a collection. 52: IEnumerator IEnumerable.GetEnumerator() 53: { 54: return GetEnumerator(); 55: } 56: } Notice, however, you can’t specify any other constructor, you can only specify that the type has a default (no argument) constructor. Summary The where clause is an excellent tool that gives your .NET generics even more power to perform tasks higher than just the base "object level" behavior.  There are a few things you cannot specify with constraints (currently) though: Cannot specify the generic type must be an enum. Cannot specify the generic type must have a certain property or method without specifying a base class or interface – that is, you can’t say that the generic must have a Start() method. Cannot specify that the generic type allows arithmetic operations. Cannot specify that the generic type requires a specific non-default constructor. In addition, you cannot overload a template definition with different, opposing constraints.  For example you can’t define a Adapter<T> where T : struct and Adapter<T> where T : class.  Hopefully, in the future we will get some of these things to make the where clause even more useful, but until then what we have is extremely valuable in making our generics more user friendly and more powerful!   Technorati Tags: C#,.NET,Little Wonders,BlackRabbitCoder,where,generics

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