Question

I use the “is” operator to find a certain class:

for(int i=0; i<screens.Count; i++){
  if(screen is ScreenBase){
    //do something...
  }
}

This works fine especially as it finds any class that inherits from the ScreenBase but not the base classes from ScreenBase.

I would like to do the same when I know only the Type and don’t want to instantiate the class:

Type screenType = GetType(line);
if (screenType is ScreenBase)

But this comparsion produces a warning as it will compare to the “Type” class.

The only alternative I know would be to compare with ==typeof but this would test only for the exact type and not the inherited ones.
Is there a way to get a similar behaviour like the “is” operator but for the type described by the Type-class?

Answer 1

If you want to know specifically if it derives from the type, use Type.IsSubclassOf(). This will not work for interfaces.

Type screenType = GetType(line);
if (screenType.IsSubclassOf(typeof(ScreenBase)))
{
    // do stuff...
}

Otherwise if you want to know if the type could be assigned to a variable of a certain type, use Type.IsAssignableFrom(). This will work for interfaces.

Type screenType = GetType(line);
if (typeof(ScreenBase).IsAssignableFrom(screenType)) // note the usage is reversed
{
    // do stuff...
}

Do note that you don’t necessarily need a type object to determine this, you can do this with an instance of the object using Type.IsInstanceOfType(). It will behave more or less like IsAssignableFrom().

if (typeof(ScreenBase).IsInstanceOfType(line)) // note the usage is reversed
{
    // do stuff...
}