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LimitPinchGestureZoom

Limit UIPinchGestureRecognizer Zoom for any UIView

The code sample shows two things (Objective-C and Swift 3):

  1. Use multiple gestures together to create a responsive user experience with media content.
  2. How to zoom using the UIPinchGestureRecognizer and limit the zoom extents as well as speed.

I have used this code in my iPhone apps/games (i.e. Bomb Dodge) and recently revised it to make it easier to use as discussed on Stack Overflow.

Video

UIGesture Video

Code

Create a view, if you use UILabel or UIImageView, you must set userInteractionEnabled = YES

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIView *blueView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 150, 150)];
    blueView.backgroundColor = [UIColor blueColor];
    [self.view addSubview:blueView];
    [self addMovementGesturesToView:blueView];
    
    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanGesture:)];
    panGesture.delegate = self;
    [blueView addGestureRecognizer:panGesture];
    
    UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handlePinchGesture:)];
    pinchGesture.delegate = self;
    [blueView addGestureRecognizer:pinchGesture];
}

Implement methods to respond to gesture messages. Pan gesture can use relative motion by reseting the translation back to (0,0).

- (void)handlePanGesture:(UIPanGestureRecognizer *)panGesture {
    CGPoint translation = [panGesture translationInView:panGesture.view.superview];
    
    if (UIGestureRecognizerStateBegan == panGesture.state ||UIGestureRecognizerStateChanged == panGesture.state) {
        panGesture.view.center = CGPointMake(panGesture.view.center.x + translation.x,
                                             panGesture.view.center.y + translation.y);
        // Reset translation, so we can get translation delta's (i.e. change in translation)
        [panGesture setTranslation:CGPointZero inView:self.view];
    }
    // Don't need any logic for ended/failed/canceled states
}

The Pinch gesture is a little more complex. This sample code shows how to apply a scale factor. If you want to change font sizes, you'll need to use different code. (Creating too many UIFont objects can slow down responsiveness)

- (void)handlePinchGesture:(UIPinchGestureRecognizer *)pinchGesture {
    
    if (UIGestureRecognizerStateBegan == pinchGesture.state ||
        UIGestureRecognizerStateChanged == pinchGesture.state) {
        
        // Use the x or y scale, they should be the same for typical zooming (non-skewing)
        float currentScale = [[pinchGesture.view.layer valueForKeyPath:@"transform.scale.x"] floatValue];
        
        // Variables to adjust the max/min values of zoom
        float minScale = 1.0;
        float maxScale = 2.0;
        float zoomSpeed = .5;
        
        float deltaScale = pinchGesture.scale;
        
        // You need to translate the zoom to 0 (origin) so that you
        // can multiply a speed factor and then translate back to "zoomSpace" around 1
        deltaScale = ((deltaScale - 1) * zoomSpeed) + 1;

        // Limit to min/max size (i.e maxScale = 2, current scale = 2, 2/2 = 1.0)
        //  A deltaScale is ~0.99 for decreasing or ~1.01 for increasing
        //  A deltaScale of 1.0 will maintain the zoom size
        deltaScale = MIN(deltaScale, maxScale / currentScale);
        deltaScale = MAX(deltaScale, minScale / currentScale);
        
        CGAffineTransform zoomTransform = CGAffineTransformScale(pinchGesture.view.transform, deltaScale, deltaScale);
        pinchGesture.view.transform = zoomTransform;
        
        // Reset to 1 for scale delta's
        //  Note: not 0, or we won't see a size: 0 * width = 0
        pinchGesture.scale = 1;
    }
}

Conform to the UIGestureRecognizerDelegate Protocol and make sure to set the delegate for each gesture you create. This method can have more complex logic, but I find that YES is enough for general photo collage type apps.

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES; // Works for most use cases of pinch + zoom + pan
}

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