AS3 - Can I know if a class implements an interfac

问题:

With this code

function someFunction(classParam:Class):Boolean
{
    // how to know if classParam implements some interface?
}

i.e. Comparing classParam with IEventDispatcher interface:

someFunction(EventDispatcher) // returns true
someFunction(Object) // returns false

I know it can't be done with is operator. But, is there a way to do it? Is there a way to know if a class implements some interface? (or is a subclass of another class?)

Possible solutions:

A. Creating an object of classParam and using that object to compare using is operator.

function someFunction(classParam:Class):Boolean
{
    return (new classParam()) is IEventDispatcher
}

B. Using describeType()

function someFunction(classParam:Class):Boolean
{
    var xml:XML = describeType(classParam)
    // found "implementsInterface" value in xml and compare to IEventDispatcher
}

There is a way that DOES NOT USE describeType or creates a new operator?

回答1:

I don't see any way to achieve what you're trying to do except by using describeType.
It has been created for this purpose, why don't you want to use it?

Edit:
It actually only takes 2 lines to do this :

var classDescription:XML = describeType(classParam);
return (classDescription.factory.implementsInterface.(@type == getQualifiedClassName(IEventDispatcher)).length() != 0);

...or just in one, if it's what bothers you:

return (describeType(classParam).factory.implementsInterface.(@type == getQualifiedClassName(IEventDispatcher)).length() != 0);

回答2:

Maybe the code samples in this article will provide an answer: Runtime Checks for Abstract Classes and Methods in ActionScript 3.0

回答3:

Adding to 'Zed-K' response. I ended up not needing the .factory part. Here is a example of a test that checks that the class is utilizing and interface. '_instance' is the class under test.

[Test]
public function testInstanceShouldBeIUser():void
{
    var classDescription:XML = describeType( _instance );
    var type:String = getQualifiedClassName(IUser);
    var xmlList:XMLList = classDescription.implementsInterface.(@type == type);
    assertTrue("expected IUser", xmlList.length() != 0 );
}

回答4:

Probably not. Btw, there is also describeTypeJSON, witch is about 5x faster than describeType.