drag image inside area

Question

i'd like to drag the image "finga" inside a region height of 320. this goes off screen:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    CGPoint location = [touch locationInView:self.view];
    if (CGRectContainsPoint(finga.frame, location)){
        CGPoint yLocation = CGPointMake(finga.center.x,location.y);
        finga.center = yLocation;
    }
}

how to define the region? thanx