How to prevent manual zooming in a UIScrollView

Question

Hopefully someone can help with this issue. I have a class derived from UIScrollView and I'd like to prevent the user from being able to zoom or scroll via manual pinch and swipe gestures. All view navigation will instead be controlled by programmatic means in response to where a user taps (think of an ebook reader where tapping on the left or right sides of the display causes the view to scroll by exactly one page width). Any suggestions on how to implement this?

Answer 1

On your - (void)viewDidLoad; you should be able to just disable whatever gesture recognizer you want. In this case:

UIPinchGestureRecognizer *pinchRecognizer = self.pinchGestureRecognizer;
pinchRecognizer.enabled = NO;

or

UIPanGestureRecognizer *panRecognizer = self.scrollView.panGestureRecognizer;
panRecognizer.enabled = NO;

I sometimes do this from view controllers that contain UIScrollViews. I just target the scroll view (self.scrollView.pinchGestureRecognizer) and temporarily disable gestures when the app. is in a certain state.

Answer 2

To prevent user-controller zooming and panning but still allow programmatic zooming and panning of a scrollview, the best approach is to override the UIScrollView's -addGestureRecognizer: method in a subclass. In my use I wanted to block all the recognizers and control the viewable area completely from my view controller, I did so like this:

-(void)addGestureRecognizer:(UIGestureRecognizer *)gestureRecognizer {
    //Prevent any of the default panning and zooming controls from working
    gestureRecognizer.enabled = NO;
    [super addGestureRecognizer:gestureRecognizer];
}

Each gesture recognizer is simply disabled, for finer control (allowing the pan control but only allow zooming via a double tap for instance) you'd simply check the incoming gesture recognizer via -isKindOfClass: and disabling as appropriate.

-(void)addGestureRecognizer:(UIGestureRecognizer *)gestureRecognizer {
    //Prevent zooming but not panning
    if ([gestureRecognizer isKindOfClass:[UIPinchGestureRecognizer class]]) {
        gestureRecognizer.enabled = NO;
    }
    [super addGestureRecognizer:gestureRecognizer];
}

I used this method in a comic reading app that uses guided navigation to animate between cropped panels on a page with the full page being contained in a UIScrollView.I can smoothly zoom in and out on a selected area by simply setting the view bounds to the region I want to display.

Answer 3

A quick note here. It seems UIScrollView's panGestureRecognizer and pinchGestureRecognizer are both enabled the first time a view controller is added to a window.

Basically what that means is setting them to enabled = NO in viewDidLoad won't work in some cases. I moved my enabled = NO to viewWillAppear: and it stuck. :)