How to tap to zoom and double tap to zoom out in iOS?

Question

I'm developing an application to display a gallery of UIImages by using a UIScrollView, my question is, how to tap to zoom and double tap to zoom out, how does it work when handling with UIScrollView.

Answer 1

You need to implement UITapGestureRecognizer - docs here - in your viewController

- (void)viewDidLoad {     [super viewDidLoad];             // what object is going to handle the gesture when it gets recognised ?     // the argument for tap is the gesture that caused this message to be sent     UITapGestureRecognizer *tapOnce = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapOnce:)];     UITapGestureRecognizer *tapTwice = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapTwice:)];      // set number of taps required     tapOnce.numberOfTapsRequired = 1;     tapTwice.numberOfTapsRequired = 2;      // stops tapOnce from overriding tapTwice     [tapOnce requireGestureRecognizerToFail:tapTwice];      // now add the gesture recogniser to a view      // this will be the view that recognises the gesture       [self.view addGestureRecognizer:tapOnce];     [self.view addGestureRecognizer:tapTwice];  } 

Basically this code is saying that when a UITapGesture is registered in self.view the method tapOnce or tapTwice will be called in self depending on if its a single or double tap. You therefore need to add these tap methods to your UIViewController:

- (void)tapOnce:(UIGestureRecognizer *)gesture {     //on a single  tap, call zoomToRect in UIScrollView     [self.myScrollView zoomToRect:rectToZoomInTo animated:NO]; } - (void)tapTwice:(UIGestureRecognizer *)gesture {     //on a double tap, call zoomToRect in UIScrollView     [self.myScrollView zoomToRect:rectToZoomOutTo animated:NO]; } 

Hope that helps