Question

I have an “PDF Viewer” in my application. I use the CGPDFDocumentRef and CGPDFPageRef to show the PDF. To zoom in the PDF I use a UIScrollView.

I am already able to pinch-zoom in the UIScrollView but I also want to be able to double-tap to zoom.

Double tap with one finger takes you to different levels in the PDF until you hit the maximumZoomLevel and then be able to double-tap with two fingers to the minimumZoomLevel.

I haven’t been able to find a solution on the Internet that shows you this in particular so I’m asking here. How could I accomplish this?

In viewDidLoad:

UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTap:)];
    [doubleTap setNumberOfTapsRequired:2];
    [self.scrollView addGestureRecognizer:doubleTap];
    [doubleTap release];

Method:

- (void)handleDoubleTap:(UIGestureRecognizer *)gestureRecognizer 
{      
    if(self.scrollView.zoomScale > self.scrollView.minimumZoomScale)
        [self.scrollView setZoomScale:self.scrollView.minimumZoomScale animated:YES]; 
    else 
        [self.scrollView setZoomScale:self.scrollView.maximumZoomScale animated:YES];
}

Answer 1

I think that you can use UITapGestureRecognizer with numberOfTapsRequired property after that in handle method (which you specify when alloc/init the recognizer) and use to use – zoomToRect:animated: or – setZoomScale:animated: on the view to zoom.

Edit: keep track on current zoom level to reverse the effect.