UIView touch location coordinates

问题:

What are the coordinates used in UIViews and their corresponding superviews? I have this code which i would like to detect a 'corridor' where the user can touch... similar to this image:alt text http://img17.imageshack.us/img17/4416/bildschirmfoto20100721u.png

This is the code i have:

    CGPoint touch = [recognizer locationInView:[shuttle superview]];
    CGPoint centre = shuttle.center;

    int outerRadius = shuttle.bounds.size.width/2;
    int innerRadius = (shuttle.bounds.size.width/2) - 30;
    if ((touch.x < outerRadius && touch.y <outerRadius)){
        NSLog(@"in outer");
        if(touch.x > innerRadius && touch.y > innerRadius) {
            NSLog(@"in corridor");  
        }
    }

The radii are approximately 500 and 600, and the touch x and y are 100 and 200...

Thus, the NSLog "in corridor" never gets called.

Thanks

回答1:

Your condition is wrong. The corridor according to it is a square, with its center at (0, 0) instead of shuttle.center. Try

CGFloat dx = touch.x - centre.x;
CGFloat dy = touch.y - centre.y;
CGFloat r2 = dx*dx + dy*dy;
if (r2 < outerRadius*outerRadius) {
  NSLog(@"in outer");
  if (r2 > innerRadius*innerRadius)
    NSLog(@"in corridor")
}

instead.

Even if the corridor is indeed expected to be a square, you should check with fabs(dx), fabs(dy) not touch.x, touch.y.