Does UIGestureRecognizer work on a UIWebView?

UIWebView has its own private views, which also has gesture recognizers attached. Hence, precedence rules keep any gesture recognizers added to a UIWebView from working properly.

One option is to implement the UIGestureRecognizerDelegate protocol and implement the method gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer. Return YES from this method for other tap gestures. This way you'll get your tap handler called, and the web view will still get its called.

See this on the Apple dev forums.


This is a somewhat hack-ish solution, but it works. UIWebView has a lot of internal gesture recognizers that you normally cannot access without using private API. You get them all for free, though, when you implement gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:. At that point, you can tell all the internal UITapGestureRecognizers to only fire when your own UITapGestureRecognizer has failed. You only do that once and then remove the delegate from your own gesture recognizer. The result is that you can still pan and scroll your webView, but it won't receive any (single) tap gestures anymore.

- (void)viewDidLoad 
{      
    [super viewDidLoad];

    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTapGesture:)];

    // view is your UIViewController's view that contains your UIWebView as a subview
    [self.view addGestureRecognizer:tap];

    tap.delegate = self;
}

- (void)handleTapGesture:(UITapGestureRecognizer *)gestureRecognizer
{
    NSLog(@"tap!");

    // this is called after gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: so we can safely remove the delegate here
    if (gestureRecognizer.delegate) {
        NSLog(@"Removing delegate...");
        gestureRecognizer.delegate = nil;
    }
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
    if ([otherGestureRecognizer isKindOfClass:[UITapGestureRecognizer class]]) {
        [otherGestureRecognizer requireGestureRecognizerToFail:gestureRecognizer];

        NSLog(@"added failure requirement to: %@", otherGestureRecognizer);
    }

    return YES;
}

Enjoy!


From what I have seen, UIWebView does not play well with others. For gesture recognizers, you could try returning YES from:

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer;

I had to be backwards compatible with 3.0 so I ended up doing all the gesture handling with Javascript inside the UIWebView. Not a good solution, but it worked for my needs. I was able to capture a long press on an element, as well as tap, swipe, pinch and rotate. Of course, I was using only local content.

Edit:

You can look in PhoneGap for an example of sending messages to the delegate of the UIWebView. In a nutshell, you use document.location = "myscheme:mycommand?myarguments" then parse out the command and arguments from this delegate callback:

-(BOOL) webView:(UIWebView *)inWeb shouldStartLoadWithRequest:(NSURLRequest *)inRequest navigationType:(UIWebViewNavigationType)inType {
  if ( [[[inRequest URL] absoluteString] hasPrefix:@"myscheme:"] ) {
    //.. parse arguments
    return NO;
  }
}

You can see in the PhoneGap code that they set up a queue and timer to send the messages. Depending on your usage, you may need to do the same thing. There are other questions on SO on this topic.

Here is the Event Handling documentation. In my case I added event listeners to document from <body onload="myloader();">

function myloader() {
    document.addEventListener( 'touchcancel' , touch_cancel , false );
    document.addEventListener( 'touchstart' , touch_start , false );
    document.addEventListener( 'touchmove' , touch_move , false );
    document.addEventListener( 'touchend' , touch_end , false );
};

The actual event handling depends a lot on your needs. Each event handler will receive a TouchEvent with a touches property where each item is a Touch. You can record the start time and location in your touchstart handler. If the touches move to far or the wrong amount of time passes it is not a long touch.

WebKit may try to handle a long touch to start a selection and copy. In your event handler you can use event.preventDefault(); to stop the default behavior. I also found the -webkit-user-select:none css property handy for some things.

var touch = {};
function touch_start( event /*TouchEvent*/ {
  event.preventDefault();
  touch = {};
  touch.startX = event.touches.item(0).pageX;
  touch.startY = event.touches.item(0).pageY;
  touch.startT = ( new Date() ).getTime();
}

This is only the second project I have used javascript with. You can find better examples elsewhere.

As you can see this is no quick answer to your problem. I am pretty happy with the results I got. The html I was working with had no interactive elements beyond a link or two.

Tags:

Objective C

Iphone

Cocoa

Ipad

Uigesturerecognizer

Recent Posts