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.NET Forum / .NET Framework / New Users / August 2007Determining if a type implements a particular interface
Hello all, When using reflection, how can I find out if a particular type implements a specific interface. For instance, I have the following code: Type t = myAsm.GetType( "AssemblyToLoad.MyClass" ); Type iMyClassType = typeof(AssemblyToLoad.IMyClass); foreach( Type i in t.GetInterfaces() ) { Console.WriteLine( "Interface: {0}; Implemented: {1}, {2}", i, iMyClassType, i.Equals( iMyClassType ) ); } The type "AssemblyToLoad.MyClass" implements an interface called "AssemblyToLoad.IMyClass", but the test "i.Equals( iMyClassType )" always returns false. The code above is in a different assembly from the "AssemblyToLoad" namespace. Thanks for your help and tips... Mario >When using reflection, how can I find out if a particular type implements a >specific interface. For instance, I have the following code: > > Type t = myAsm.GetType( "AssemblyToLoad.MyClass" ); > Type iMyClassType = typeof(AssemblyToLoad.IMyClass); Why are you using Assembly.GetType for the class and typeof for the interface if they are both defined in the same assembly? Is there any chance you have two separate definitions of the IMyClass interface? BTW I like to use Type.IsAssignableFrom rather than looping through all interfaces. Mattias  SignatureMattias Sjögren [C# MVP] mattias @ mvps.org http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com Please reply only to the newsgroup. The class AssemblyToLoad.MyClass and interface AssemblyToLoad.IMyclass are defined in an assembly different from my client application. I am emperimenting with loading a class defined in a separate assembly from my client application that shares a common interface type. In my example, that common interface is IMyClass. What I would like to do is create a system where different implementations of an interface I am desigining can be loaded at runtime using reflection or any other means. Reflection is a new field for me. I am also trying to use the Activator.CreateInstanceFrom( string, string ) method to accomplish my goal in a much more concise manner, but I get an InvalidCastException. I am duplicating the example code shown in the documentation for the Activator.CreateInstanceFrom(string, string, object[]) overloaded method. I don't think I have two separate definitions of the same interface. I'll check again. I'll look at the documentation for Type.IsAssignableFrom. Thanks so much for sharing that tip. Mario > >When using reflection, how can I find out if a particular type implements > >a [quoted text clipped - 13 lines] > > Mattias > loading a class defined in a separate assembly [...] create a system where > different implementations of an interface I am desigining can be loaded > at runtime using reflection [...] use the Activator.CreateInstanceFrom([...]) > [...] InvalidCastException. Just to reassure you: this is a pretty standard way to do it. It's sometimes called the object builder pattern, I think. If you get casting errors, make sure your references are correct, and that you have no redundant DLLs, or old DLLs lying around, accidentally being used. If you load an existing assembly from disk, make sure you specify the correct assembly details. This is a typical scenario with three assemblies, from the top of my head: 1. ObjectBuilder assembly references assembly which contains IClass and assembly which contains Class 2. Client assembly references assembly which contains IClass and assembly which contains IClass 3. Client does IClass classInstance = ObjectBuilder<IClass>.Build(), upon which ObjectBuilder uses reflection to CreateInstance() of Class, casting it as IClass, and returning it. I've used a shortcut from System.Web.dll sometimes: http://msdn2.microsoft.com/en-us/library/system.web.compilation.buildmanager_met hods.aspx It does iteration over assemblies and types to find a specified type, which you might end up doing yourself otherwise, if you want a real System.Type. Thank you all for your contributions! >> loading a class defined in a separate assembly [...] create a system >> where [quoted text clipped - 28 lines] > which you might end up doing yourself otherwise, if you want a real > System.Type. Use the "is" operator: if (i is iMyClassType) ... SignatureHTH, Kevin Spencer Microsoft MVP DSI PrintManager, Miradyne Component Libraries: http://www.miradyne.net > Hello all, > [quoted text clipped - 19 lines] > > Mario >Use the "is" operator: > >if (i is iMyClassType) ... Not in this case, where iMyClassType is a System.Type instance. Mattias SignatureMattias Sjögren [C# MVP] mattias @ mvps.org http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com Please reply only to the newsgroup. On Aug 14, 4:10 pm, Mattias Sj?gren <mattias.dont.want.s...@mvps.org> wrote: >> if (i is iMyClassType) ... > > Not in this case, where iMyClassType is a System.Type instance. Also, the correct form is "i am", not "i is". The new Code Analysis in Visual Studio 2008 would generate a OperatorShouldBeVerbedCorrectly warning for this error. Since when has "am" been a keyword in C#/.Net ? I think you've misread the code slightly. Something more readable might be : public void DoSomething(object obj) { if( obj is iMyClassType ) { } } HTH Ged On Aug 14, 4:10 pm, Mattias Sjögren <mattias.dont.want.s...@mvps.org> wrote: >> if (i is iMyClassType) ... > > Not in this case, where iMyClassType is a System.Type instance. Also, the correct form is "i am", not "i is". The new Code Analysis in Visual Studio 2008 would generate a OperatorShouldBeVerbedCorrectly warning for this error. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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