I don't understand the concept of selectors

[Russell]

I don't understand the details of why and how to use selectors in objective -c. I understand that at runtime messages are 'converted' to selectors. But I don't understand why I should use them in practice. For example what is the purpose of calling the animateBall method in the initializerTimer method using a selector?


-

(void)animateBall:(NSTimer *)theTimer {

	ball.center = CGPointMake(ball.center.x +ballMovement.x,
		ball.center.y + ballMovement.y);
}

-

(void)initializeTimer
{
	float theInterval = 1.0/30.0;
	[NSTimer scheduledTimerWithTimeInterval:theInterval target:self selector:@selector(animateBall:) userInfo:nil repeats: YES];

}

[RLScott]

A selector is essentially a pointer to a method (except that it points to the name rather than to the implementation). It is used anywhere you need to specify which method should be called in a certain circumstance. If you are calling the method right now, then you can refer to it directly and there is no need for a selector. But if you are setting up something to be called at a later time, then you would have to specify that method with a selector.