创建一个可任意拖放的控件

 1 - (void)viewDidLoad {
 2     [super viewDidLoad];
 3     
 4     //初始化button
 5     _button = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
 6     _button.backgroundColor     = [UIColor redColor];
 7     _button.layer.cornerRadius  = 50;
 8     _button.layer.masksToBounds = YES;
 9     _button.center              = self.view.center;
10     
11     [self.view addSubview:_button];
12     
13     UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanGesture:)];
14     [self.button addGestureRecognizer:panGesture];
15 }
16 
17 - (void)handlePanGesture: (UIPanGestureRecognizer *)recognizer {
18     
19     CGPoint translation    = [recognizer translationInView:self.view];
20     recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,
21                                          recognizer.view.center.y + translation.y);
22     [recognizer setTranslation:CGPointMake(0, 0) inView:self.view];
23 }