Question

In .Net when I have an object that has an event I can register to handle that event via a delegate:

void Test()
{
    Button button = new Button();
    button.Click  += new EventHandler(OnClick);
}
void OnClick(object sender, EventArgs e)
{
    text1.Text = "The Button Was Clicked";
}

How do I do this sort of thing in Objective-C? Specifically I’m trying to handle the ccTouchEnded of a SneakyButton. I thought it would be something like this:

SneakyButton* mybutton = [SneakyButton button];
[mybutton ccTouchEnded:self.onButtonDown];

- (void)onButtonDown:(UITouch *)touch withEvent:(UIEvent *)event
{
    CCLOG(@"The Button Was Clicked");
}

Answer 1

Cocoa and CocoaTouch often uses “Target/Action”.

• Target: an objc object. the target is what gets messaged.
• Action: a selector. the action is the selector to message the target with.

In that sense, the action is the equivalent.

When the target/action is performed, it would take this general form:

[target performSelector:action withObject:someParameter];

of course, the parameter list will vary in the real world.

The UIControl class is quite small – read it for more info on the subject. It will give you a good idea of a control’s target/action support and the interfaces you’ll use for handling these events. NSControl is the Cocoa counterpart, but that’s a much larger class – it defines much more than Target/Action interfaces.