I've made this extension method to check if a type implements an interface. For it to work correctly it needs to compare 2 types. This comparison however doesn't seem to work realiably:
public static bool ImplementsInterface(this Type type, Type testInterface)
{
if (testInterface.GenericTypeArguments.Length > 0)
{
return testInterface.IsAssignableFrom(type);
}
else
{
foreach (var @interface in type.GetInterfaces())
{
// This doesn't always work:
if (@interface == testInterface)
// But comparing the names instead always works!
// if (@interface.Name == testInterface.Name)
{
return true;
}
}
return false;
}
}
This is the case where my comparison fails:
public static class TestInterfaceExtensions
{
interface I1 { }
interface I2<T> : I1 { }
class Class1Int : I2<int> { }
[Fact]
public void ImplementsInterface()
{
Assert.True(typeof(Class1Int).ImplementsInterface(typeof(I2<>)));
}
}
As mentioned in the comment, if I compare the type names then it always works as expected. I would like to know what's going on here.
If the interface is generic you need to be comparing back to the generic type definition:
public static bool ImplementsInterface(this Type type, Type testInterface)
{
if (testInterface.GenericTypeArguments.Length > 0)
{
return testInterface.IsAssignableFrom(type);
}
else
{
foreach (var @interface in type.GetInterfaces())
{
var compareType = @interface.IsGenericType
? @interface.GetGenericTypeDefinition()
: @interface;
if (compareType == testInterface)
{
return true;
}
}
return false;
}
}
This works for a bunch of test cases:
Console.WriteLine(typeof(Class1Int).ImplementsInterface(typeof(I2<>))); // True
Console.WriteLine(typeof(Class1Int).ImplementsInterface(typeof(I2<int>))); // True
Console.WriteLine(typeof(Class1Int).ImplementsInterface(typeof(I2<bool>))); // False
Console.WriteLine(typeof(Class1Int).ImplementsInterface(typeof(I1))); // True
Console.WriteLine(typeof(Class1Int).ImplementsInterface(typeof(I3))); // False
Live example: https://dotnetfiddle.net/bBslxH