Class cluster initialization

Question

My iPhone app has an abstract class WorkingView. It is a subclass of UIView. WorkingView will in turn have a bunch of concrete subclasses. Two of those will be SimplifyView and MultiplyView.

I am trying to write the method that creates new instances of WorkingView. This method should have the mode passed in and return an instance of the appropriate concrete subclass. Per the answer to this question, this is what I have so far:

+ (id)newWorkingViewWithFrame:(CGRect)frame mode: (modeEnum) mode {
    WorkingView *ret;
    switch (mode) {
        case simplifyMode:
            ret = [[SimplifyView alloc]initWithFrame: frame];
            break;
        case multiplyMode:
            ret = [[MultiplyView alloc]initWithFrame: frame];
            break;
        // additional cases here
        default:
            return nil;
    }
    // more initialization here
    return ret;
}

So far, so good. But here is the problem. In SimplifyView's init method, I need to run the object through UIView's init method. Calling [super initWithFrame: frame] gets me only to WorkingView, not all the way to UIView. I suppose I could create an initWithFrame: method in WorkingView that in turn calls UIView's initWithFrame: method -- but that feels hackish.

What is the appropriate way to handle this?

Answer 1

If you call [super initWithFrame:frame] from your subclass, the runtime will climb the inheritance hierarchy looking for a class that implements that method, starting with super. If super doesn't implement initWithFrame:, the runtime will keep climbing until it eventually finds and invokes the default implementation in UIView.