Question

I am following Apple’s ScrollSuite example, however pinch to zoom is not working. I am not sure whats wrong:

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];

    // set up main scroll view
    imageScrollView = [[UIScrollView alloc] initWithFrame:[[self view] bounds]];
    [imageScrollView setBackgroundColor:[UIColor blackColor]];
    [imageScrollView setDelegate:self];
    [imageScrollView setBouncesZoom:YES];
    [[self view] addSubview:imageScrollView];

    // add touch-sensitive image view to the scroll view
    UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"default.png"]];
    [imageView setTag:ZOOM_VIEW_TAG];
    [imageView setUserInteractionEnabled:YES];
    [imageScrollView setContentSize:[imageView frame].size];
    [imageScrollView addSubview:imageView];
    [imageView release];

    // calculate minimum scale to perfectly fit image width, and begin at that scale
    float minimumScale = [imageScrollView frame].size.width  / [imageView frame].size.width;
    [imageScrollView setMinimumZoomScale:minimumScale];
    [imageScrollView setZoomScale:minimumScale];

    //[self.imageView loadImageFromURL:self.url];
}



// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    //return (interfaceOrientation == UIInterfaceOrientationPortrait);
    if (enableLandscapeOrientation) {
        [[self navigationController] setNavigationBarHidden:UIInterfaceOrientationIsLandscape(interfaceOrientation) animated:YES];
        return YES;
    }
    else {
        return NO;
    }
}


#pragma mark UIScrollViewDelegate methods

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    return [imageScrollView viewWithTag:ZOOM_VIEW_TAG];
}

/************************************** NOTE **************************************/
/* The following delegate method works around a known bug in zoomToRect:animated: */
/* In the next release after 3.0 this workaround will no longer be necessary      */
/**********************************************************************************/
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
    [scrollView setZoomScale:scale+0.01 animated:NO];
    [scrollView setZoomScale:scale animated:NO];
}

#pragma mark Utility methods

- (CGRect)zoomRectForScale:(float)scale withCenter:(CGPoint)center {

    CGRect zoomRect;

    // the zoom rect is in the content view's coordinates. 
    //    At a zoom scale of 1.0, it would be the size of the imageScrollView's bounds.
    //    As the zoom scale decreases, so more content is visible, the size of the rect grows.
    zoomRect.size.height = [imageScrollView frame].size.height / scale;
    zoomRect.size.width  = [imageScrollView frame].size.width  / scale;

    // choose an origin so as to get the right center.
    zoomRect.origin.x    = center.x - (zoomRect.size.width  / 2.0);
    zoomRect.origin.y    = center.y - (zoomRect.size.height / 2.0);

    return zoomRect;
}

Answer 1

Double check your value for minimumScale. Based on that code and guessing at what “default.png” is, I’d say your minimumScale will likely be 1.0 which means your scroll view has no zoom range. Try doing this just to see if it works:

[imageScrollView setMinimumZoomScale:0.5f];
[imageScrollView setMaximumZoomScale:2.0f];