How to Zoom In/Out Photo on double Tap in the iPhone WWDC 2010 - 104 PhotoScroller

Question

I am going through the Sample code of iPhone WWDC 2010 - 104 PhotoScroller App. It's working great with my project related images (PDF Page Images)

but I am struggling detect touches in the PhotoScroller App. The Zooming using multiple touches is handled by the ScrollVoiew. Now I want to Zoom In/out the photo on double Tap. The Touchesbegan method is being called in TilingView Class. Then I used [super touchesbegan: withevent:] and now the touches are in the ImageScrollView Class.

How to get these touch events in PhotoViewController. How to achieve the zoom in and zoom out on touch ?

Can anyone help in this Regard ?

Answer 1

I researched several different web sites and I came up with the following...

Place this code into your viewDidLoad or viewWillAppear method:

//////////////////////////////
// Listen for Double Tap Zoom

UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTap:)];

[doubleTap setNumberOfTapsRequired:2];

[self.scrollView addGestureRecognizer:doubleTap];

[doubleTap release];

Add this to your header file:

- (void)handleDoubleTap:(UIGestureRecognizer *)gestureRecognizer;

Add this to your implementation:

- (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]; 

  }  

Currently this does not center upon the area where the user double tapped.