objective-C中触发事件

需要实现如下功能：将可拖拽的按钮拖拽到屏幕的指定位置时，自动触发一个事件。不知道应该从哪儿入手，

UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[btn1 setFrame:CGRectMake(10.0f, 300.0f, 300.0f, 42.0f)];
[btn1 setTitle:[NSString stringWithFormat:@"View Fullscreen Decor"] forState:UIControlStateNormal];
[btn1 addTarget:self action:@selector(imageMoved:withEvent:) forControlEvents:UIControlEventTouchDragInside];
[self.view addSubview:btn1];
[super viewDidLoad];
[myScrollView addSubview:btn1];

- (IBAction) imageMoved:(id) sender withEvent:(UIEvent *) event
{
CGPoint point = [[[event allTouches] anyObject] locationInView:self.view];
UIControl *control = sender;
control.center = point;
}