移动UIButton

-(void)viewDidLoad 
{
   [super viewDidLoad];

   // create a new button
   UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
   [button setTitle:@"Drag me!" forState:UIControlStateNormal];

   // add drag listener
   [button addTarget:self action:@selector(wasDragged:withEvent:)
       forControlEvents:UIControlEventTouchDragInside];

   // center and size
   button.frame = CGRectMake((self.view.bounds.size.width - 100)/2.0,
            (self.view.bounds.size.height - 50)/2.0,
           100, 50);

   // add it, centered
   [self.view addSubview:button];
}

-(void)wasDragged:(UIButton *)button withEvent:(UIEvent *)event
{
   // get the touch
   UITouch *touch = [[event touchesForView:button] anyObject];

   // get delta
   CGPoint previousLocation = [touch previousLocationInView:button];
   CGPoint location = [touch locationInView:button];
   CGFloat delta_x = location.x - previousLocation.x;
   CGFloat delta_y = location.y - previousLocation.y;

   // move button
   button.center = CGPointMake(button.center.x + delta_x,
       button.center.y + delta_y);
}