How to determine if a type implements an interface with C reflection

Question

Does reflection in C  offer a way to determine if some given System Type type models some interface   public interface IMyInterface     public class MyType   IMyInterface        should yield  true  typeof MyType             MODELS INTERFACE IMyInterface

User · Answer

If you don t need to use reflection and you have an object  you can use this  if myObject is IMyInterface         it s implementing IMyInterface

User · Answer

What about   typeof IWhatever  GetTypeInfo   IsInterface

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public static bool ImplementsInterface this Type type  Type ifaceType         Type   intf   type GetInterfaces        for int i   0  i  lt  intf Length  i                   if intf  i      ifaceType                         return true                      return false      I think this is the correct release  for three reasons      It uses GetInterfaces and not IsAssignableFrom  it s faster since IsAssignableFrom eventually after several checks does call GetInterfaces  It iterates over the local array  so there will be no bounds checks  It uses the    operator which is defined for Type  so probably is safer than the Equals method  that the Contains call  will eventually use

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If you have a type or an instance you can easily check if they support a specific interface   To test if an object implements a certain interface   if myObject is IMyInterface         object myObject implements IMyInterface     To test if a type implements a certain interface   if typeof IMyInterface  IsAssignableFrom typeof MyType           type MyType implements IMyInterface     If you got a generic object and want to do a cast as well as a check if the interface you cast to is implemented the code is    var myCastedObject   myObject as IMyInterface       if myCastedObject    null             object myObject implements IMyInterface

User · Answer

As someone else already mentioned  Benjamin Apr 10  13 at 22 21      It sure was easy to not pay attention and get the arguments for   IsAssignableFrom backwards  I will go with GetInterfaces now  p       Well  another way around is just to create a short extension method that fulfills  to some extent  the  most usual  way of thinking  and agreed this is a very little personal choice to make it slightly  more natural  based on one s preferences    public static class TypeExtensions       public static bool IsAssignableTo this Type type  Type assignableType                return assignableType IsAssignableFrom type             And why not going a bit more generic  well not sure if it is really that interesting  well I assume I m just passing another pinch of  syntaxing  sugar    public static class TypeExtensions       public static bool IsAssignableTo this Type type  Type assignableType                return assignableType IsAssignableFrom type              public static bool IsAssignableTo lt TAssignable gt  this Type type                return IsAssignableTo type  typeof TAssignable              I think it might be much more natural that way  but once again just a matter of very personal opinions   var isTrue   michelleType IsAssignableTo lt IMaBelle gt

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IsAssignableFrom is now moved to TypeInfo   typeof ISMSRequest  GetTypeInfo   IsAssignableFrom typeof T  GetTypeInfo

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I just did   public static bool Implements lt I gt  this Type source  where I   class     return typeof I  IsAssignableFrom source       I wish I could have said where I   interface  but interface is not a generic parameter constraint option  class is as close as it gets   Usage   if MyType Implements lt IInitializable gt       MyCollection Initialize      I just said Implements because that s more intuitive  I always get IsAssignableFrom flip-flopped

User · Answer

You have a few choices    typeof IMyInterface  IsAssignableFrom typeof MyType   typeof MyType  GetInterfaces   Contains typeof IMyInterface     For a generic interface  it   s a bit different    typeof MyType  GetInterfaces   Any i   gt  i IsGenericType  amp  amp  i GetGenericTypeDefinition      typeof IMyInterface lt  gt

User · Answer

Use Type IsAssignableFrom   typeof IMyInterface  IsAssignableFrom typeof MyType

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Note that if you have a generic interface IMyInterface lt T gt  then this will always return false     typeof IMyInterface lt  gt   IsAssignableFrom typeof MyType      ALWAYS FALSE      This doesn t work either     typeof MyType  GetInterfaces   Contains typeof IMyInterface lt  gt        ALWAYS FALSE      However  if MyType implements IMyInterface lt MyType gt  this works and returns true     typeof IMyInterface lt MyType gt   IsAssignableFrom typeof MyType     However  you likely will not know the type parameter T at runtime  A somewhat hacky solution is     typeof MyType  GetInterfaces                    Any x  gt x Name    typeof IMyInterface lt  gt   Name    Jeff s solution is a bit less hacky     typeof MyType  GetInterfaces             Any i   gt  i IsGenericType                amp  amp  i GetGenericTypeDefinition      typeof IMyInterface lt  gt       Here s a extension method on Type that works for any case   public static class TypeExtensions       public static bool IsImplementing this Type type  Type someInterface                return type GetInterfaces                 Any i   gt  i    someInterface                      i IsGenericType                       amp  amp  i GetGenericTypeDefinition      someInterface              Note that the above uses linq  which is probably slower than a loop    You can then do      typeof MyType  IsImplementing IMyInterface lt  gt

User · Answer

Modifying Jeff s answer for optimal performance  thanks to performance test by Pierre Arnaud    var type   typeof MyType   var implementsInterface   typeof IMyInterface  IsAssignableFrom type   amp  amp  type IsClass    To find all types that implement an interface in a given Assembly   var implementations   typeof TypeInTargetAssembly  Assembly GetTypes                              Where t   gt  typeof IMyInterface  IsAssignableFrom t   amp  amp  t IsClass

User · Answer

Use Type IsAssignableTo  as of  NET 5 0   typeof MyType  IsAssignableTo typeof IMyInterface     As stated in a couple of comments IsAssignableFrom may be considered confusing by being  quot backwards quot

User · Answer

what about   if MyType as IMyInterface    null

User · Answer

typeof IMyInterface  IsAssignableFrom someclass GetType       or  typeof IMyInterface  IsAssignableFrom typeof MyType

User · Answer

A correct answer is  typeof MyType  GetInterface nameof IMyInterface      null    However    typeof MyType  IsAssignableFrom typeof IMyInterface      might return a wrong result  as the following code shows with string and IConvertible       static void TestIConvertible                 string test    test           Type stringType   typeof string      or test GetType             bool isConvertibleDirect   test is IConvertible          bool isConvertibleTypeAssignable   stringType IsAssignableFrom typeof IConvertible            bool isConvertibleHasInterface   stringType GetInterface nameof IConvertible      null           Console WriteLine   isConvertibleDirect   isConvertibleDirect             Console WriteLine   isConvertibleTypeAssignable   isConvertibleTypeAssignable             Console WriteLine   isConvertibleHasInterface   isConvertibleHasInterface             Results     isConvertibleDirect  True  isConvertibleTypeAssignable  False  isConvertibleHasInterface  True

User · Answer

Anyone searching for this might find the following extension method useful   public static class TypeExtensions       public static bool ImplementsInterface this Type type  Type  interface                if  type    null                        throw new ArgumentNullException nameof type                       if   interface    null                        throw new ArgumentNullException nameof  interface                       var interfaces   type GetInterfaces            if   interface IsGenericTypeDefinition                        foreach  var item in interfaces                                if  item IsConstructedGenericType  amp  amp  item GetGenericTypeDefinition       interface                                        return true                                                    else                       foreach  var item in interfaces                                if  item     interface                                        return true                                                     return false            xunit tests   public class TypeExtensionTests        Theory       InlineData typeof string   typeof IList lt int gt    false        InlineData typeof List lt  gt    typeof IList lt int gt    false        InlineData typeof List lt  gt    typeof IList lt  gt    true        InlineData typeof List lt int gt    typeof IList lt  gt    true        InlineData typeof List lt int gt    typeof IList lt int gt    true        InlineData typeof List lt int gt    typeof IList lt string gt    false       public void ValidateTypeImplementsInterface Type type  Type  interface  bool expect                var output   type ImplementsInterface  interface           Assert Equal expect  output

[c#] How to determine if a type implements an interface with C# reflection

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