NSSet use predicate to return objects matching given class

问题

Let's say I have an NSSet that contains a collection of objects of type id<Shape>

. . . of which there are CircleShape, SquareShape, HexagonalShape instances put into it (not the real protocol or class names) . .

is it possible to use a predicate or another single line of code to return all of the instances of CircleShape?

回答1:

You can use a block-based predicate like this:

NSSet *yourSet = ...;
NSPredicate *pred = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
    return [evaluatedObject isKindOfClass:[CircleShape class]];
}];
NSSet *filteredSet = [yourSet filteredSetUsingPredicate:pred];

This would return all instances of CircleShape or subclasses of CircleShape. Use isMemberOfClass if you want only instances of the class, but not of subclasses.

来源：https://stackoverflow.com/questions/14276018/nsset-use-predicate-to-return-objects-matching-given-class