iOS 7 Programming Cookbook

10.6. Detecting Pinch Gestures

Problem

You want your users to be able to perform pinch gesture on a view.

Solution

Create an instance of the UIPinchGestureRecognizer class and add it to your target view, using the addGestureRecognizer: instance method of the UIView class:

- (void)viewDidLoad {
    [super viewDidLoad];
    
    CGRect labelRect = CGRectMake(0.0f,     /* X */
                                  0.0f,     /* Y */
                                  200.0f,   /* Width */
                                  200.0f);  /* Height */
    
    self.myBlackLabel = [[UILabel alloc] initWithFrame:labelRect];
    self.myBlackLabel.center = self.view.center;
    self.myBlackLabel.backgroundColor = [UIColor blackColor];
    
    /* Without this line, our pinch gesture recognizer
     will not work */
    self.myBlackLabel.userInteractionEnabled = YES;
    [self.view addSubview:self.myBlackLabel];
    
    /* Create the Pinch Gesture Recognizer */
    self.pinchGestureRecognizer =  [[UIPinchGestureRecognizer alloc]
                                    initWithTarget:self
                                    action:@selector(handlePinches:)];
    
    /* Add this gesture recognizer to our view */
    [self.myBlackLabel 
     addGestureRecognizer:self.pinchGestureRecognizer];
    
}

The view controller is defined in this way:

#import "ViewController.h"

@interface ViewController ()
@property (nonatomic, strong)
    UIPinchGestureRecognizer *pinchGestureRecognizer;
@property (nonatomic, strong) UILabel *myBlackLabel;
@property (nonatomic, unsafe_unretained) CGFloat currentScale;
@end

Discussion

Pinching allows users to scale GUI elements up and down easily. For instance, the Safari web browser on iOS allows users to pinch on a web page in order to zoom into the contents ...