iOS 6 Programming Cookbook

8.3. Detecting Panning and Dragging Gestures

Problem

You want the users of your application to be able to move GUI elements around using their fingers.

Note

Pan gestures are continuous movements of fingers on the screen; recall that swipe gestures were discrete gestures. This means the method set as the target method of a pan gesture recognizer gets called repeatedly from the beginning to the end of the recognition process.

Solution

Use the UIPanGestureRecognizer class:

- (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,  /* Width */
                                 100.0f); /* Height */
  
  self.helloWorldLabel = [[UILabel alloc] initWithFrame:labelFrame];
  self.helloWorldLabel.text = @"Hello World";
  self.helloWorldLabel.backgroundColor = [UIColor blackColor];
  self.helloWorldLabel.textColor = [UIColor whiteColor];
  self.helloWorldLabel.textAlignment = UITextAlignmentCenter;
  
  /* Make sure to enable user interaction; otherwise, tap events
   won't be caught on this label */
  self.helloWorldLabel.userInteractionEnabled = YES;
  
  /* And now make sure this label gets displayed on the view */
  [self.view addSubview:self.helloWorldLabel];
  
  /* Create the Pan Gesture Recognizer */
  self.panGestureRecognizer = [[UIPanGestureRecognizer alloc] 
                               initWithTarget:self
                               action:@selector(handlePanGestures:)];
  
  /* At least and at most we need only one finger to activate
   the pan gesture recognizer */
  self.panGestureRecognizer ...