1 前言
利用 UIPanGestureRecognizer 這個手勢識別器, 來實現圖層的拖拽。

2 代碼實例
ZYViewController.m

[plain]
@synthesize helloWorldLabel; 
@synthesize panGestureRecognizer; 
 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    self.view.backgroundColor = [UIColor whiteColor]; 
    /* Let's first create a label */ 
    CGRect labelFrame = CGRectMake(0.0f, /* X */ 
                                   0.0f, /* Y */ 
                                   150.0f, /* 寬 */ 
                                   100.0f); /* 高 */ 
    self.helloWorldLabel = [[UILabel alloc] initWithFrame:labelFrame]; 
    self.helloWorldLabel.text = @"Hello World"; 
    self.helloWorldLabel.backgroundColor = [UIColor blackColor]; 
    self.helloWorldLabel.textColor = [UIColor whiteColor]; 
    self.helloWorldLabel.textAlignment = NSTextAlignmentCenter; 
    //確保label可以互動的屬性，以便可以激活其方法 
    self.helloWorldLabel.userInteractionEnabled = YES; 
    [self.view addSubview:self.helloWorldLabel]; 
    //創建拖拽手勢 
    self.panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self 
                                                                action:@selector(handlePanGestures:)]; 
    //無論最大還是最小都只允許一個手指 
    self.panGestureRecognizer.minimumNumberOfTouches = 1; 
    self.panGestureRecognizer.maximumNumberOfTouches = 1; 
    [self.helloWorldLabel addGestureRecognizer:self.panGestureRecognizer]; 
} 
 
- (void) handlePanGestures:(UIPanGestureRecognizer*)paramSender{ 
    if (paramSender.state != UIGestureRecognizerStateEnded && paramSender.state != UIGestureRecognizerStateFailed){ 
        //通過使用 locationInView 這個方法,來獲取到手勢的坐標 
        CGPoint location = [paramSender locationInView:paramSender.view.superview]; 
        paramSender.view.center = location; 
    } 
} 

@synthesize helloWorldLabel;
@synthesize panGestureRecognizer;

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    /* Let's first create a label */
    CGRect labelFrame = CGRectMake(0.0f, /* X */
                                   0.0f, /* Y */
                                   150.0f, /* 寬 */
                                   100.0f); /* 高 */
    self.helloWorldLabel = [[UILabel alloc] initWithFrame:labelFrame];
    self.helloWorldLabel.text = @"Hello World";
    self.helloWorldLabel.backgroundColor = [UIColor blackColor];
    self.helloWorldLabel.textColor = [UIColor whiteColor];
    self.helloWorldLabel.textAlignment = NSTextAlignmentCenter;
    //確保label可以互動的屬性，以便可以激活其方法
    self.helloWorldLabel.userInteractionEnabled = YES;
    [self.view addSubview:self.helloWorldLabel];
    //創建拖拽手勢
    self.panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self
                                                                action:@selector(handlePanGestures:)];
    //無論最大還是最小都只允許一個手指
    self.panGestureRecognizer.minimumNumberOfTouches = 1;
    self.panGestureRecognizer.maximumNumberOfTouches = 1;
    [self.helloWorldLabel addGestureRecognizer:self.panGestureRecognizer];
}

- (void) handlePanGestures:(UIPanGestureRecognizer*)paramSender{
    if (paramSender.state != UIGestureRecognizerStateEnded && paramSender.state != UIGestureRecognizerStateFailed){
        //通過使用 locationInView 這個方法,來獲取到手勢的坐標
        CGPoint location = [paramSender locationInView:paramSender.view.superview];
        paramSender.view.center = location;
    }
}
運行結果

拖拽後結果