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);
This question is related to
c#
reflection
interface
What about
typeof(IWhatever).GetTypeInfo().IsInterface
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 "backwards".
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<TAssignable>(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<IMaBelle>();
what about
if(MyType as IMyInterface != null)
?
Modifying Jeff's answer for optimal performance (thanks to performance test by Pierre Arnaud):
var type = typeof(MyType);
var implementsInterface = typeof(IMyInterface).IsAssignableFrom(type) && type.IsClass;
To find all types that implement an interface in a given Assembly
:
var implementations = typeof(TypeInTargetAssembly).Assembly.GetTypes()
.Where(t => typeof(IMyInterface).IsAssignableFrom(t) && t.IsClass);
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
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
}
Note that if you have a generic interface IMyInterface<T>
then this will always return false
:
typeof(IMyInterface<>).IsAssignableFrom(typeof(MyType)) /* ALWAYS FALSE */
This doesn't work either:
typeof(MyType).GetInterfaces().Contains(typeof(IMyInterface<>)) /* ALWAYS FALSE */
However, if MyType
implements IMyInterface<MyType>
this works and returns true
:
typeof(IMyInterface<MyType>).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=>x.Name == typeof(IMyInterface<>).Name)
Jeff's solution is a bit less hacky:
typeof(MyType).GetInterfaces()
.Any(i => i.IsGenericType
&& i.GetGenericTypeDefinition() == typeof(IMyInterface<>));
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 => i == someInterface
|| i.IsGenericType
&& i.GetGenericTypeDefinition() == someInterface);
}
}
(Note that the above uses linq, which is probably slower than a loop.)
You can then do:
typeof(MyType).IsImplementing(IMyInterface<>)
I just did:
public static bool Implements<I>(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<IInitializable>())
MyCollection.Initialize();
I just said Implements
because that's more intuitive. I always get IsAssignableFrom
flip-flopped.
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
}
public static bool ImplementsInterface(this Type type, Type ifaceType)
{
Type[] intf = type.GetInterfaces();
for(int i = 0; i < intf.Length; i++)
{
if(intf[ i ] == ifaceType)
{
return true;
}
}
return false;
}
I think this is the correct release, for three reasons:
IsAssignableFrom
is now moved to TypeInfo
:
typeof(ISMSRequest).GetTypeInfo().IsAssignableFrom(typeof(T).GetTypeInfo());
typeof(IMyInterface).IsAssignableFrom(typeof(MyType));
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 && 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<int>), false)]
[InlineData(typeof(List<>), typeof(IList<int>), false)]
[InlineData(typeof(List<>), typeof(IList<>), true)]
[InlineData(typeof(List<int>), typeof(IList<>), true)]
[InlineData(typeof(List<int>), typeof(IList<int>), true)]
[InlineData(typeof(List<int>), typeof(IList<string>), false)]
public void ValidateTypeImplementsInterface(Type type, Type @interface, bool expect)
{
var output = type.ImplementsInterface(@interface);
Assert.Equal(expect, output);
}
}
typeof(IMyInterface).IsAssignableFrom(someclass.GetType());
or
typeof(IMyInterface).IsAssignableFrom(typeof(MyType));
Source: Stackoverflow.com