UIImageView and UIScrollView zooming

Question

Do I actually need a UIPinchGestureRecognizer inside a UIScrollView to have the pinch working? If yes how do I do it? I am trying to implement what flipboard has, where it b

Answer 1

I did a custom image viewer not a long ago without the pinch recognizers. Just UIImageView on top of UIScrollView. There you pass a string with a link to the image and it also has a progress bar. Once that image is finished loading the image is shown. Here's the code:

-(UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
  return self.theImageView;
}

- (CGRect)centeredFrameForScrollView:(UIScrollView *)scroll andUIView:(UIView *)rView {
  CGSize boundsSize = scroll.bounds.size;
  CGRect frameToCenter = rView.frame;
  // center horizontally
  if (frameToCenter.size.width < boundsSize.width) {
    frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
  }
  else {
    frameToCenter.origin.x = 0;
  }
  // center vertically
  if (frameToCenter.size.height < boundsSize.height) {
    frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
  }
  else {
    frameToCenter.origin.y = 0;
  }
  return frameToCenter;
}

-(void)scrollViewDidZoom:(UIScrollView *)scrollView
{
  self.theImageView.frame = [self centeredFrameForScrollView:self.theScrollView andUIView:self.theImageView];                               
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
  [self.resourceData setLength:0];
  self.filesize = [NSNumber numberWithLongLong:[response expectedContentLength]];
}

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
  [self.resourceData appendData:data];
  NSNumber *resourceLength = [NSNumber numberWithUnsignedInteger:[self.resourceData length]];
  self.progressBar.progress = [resourceLength floatValue] / [self.filesize floatValue];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
  self.theImage = [[UIImage alloc]initWithData:resourceData];
  self.theImageView.frame = CGRectMake(0, 0, self.theImage.size.width, self.theImage.size.height);
  self.theImageView.image = self.theImage;
  self.theScrollView.minimumZoomScale = self.theScrollView.frame.size.width / self.theImageView.frame.size.width;
  self.theScrollView.maximumZoomScale = 2.0;
  [self.theScrollView setZoomScale:self.theScrollView.minimumZoomScale];
  self.theScrollView.contentSize = self.theImageView.frame.size;
  self.theLabel.hidden = YES;
  self.progressBar.hidden = YES;
}

-(void)setImageInImageView
{
  NSURLRequest *req = [[NSURLRequest alloc]initWithURL:[NSURL URLWithString:self.imageLink]];
  NSURLConnection *conn = [[NSURLConnection alloc]initWithRequest:req delegate:self];
  if (conn)
  {
    self.resourceData = [NSMutableData data];
  }
  else
  {
    NSLog(@"Connection failed: IMageViewerViewController");
  }
}

-(void)loadView
{
  self.filesize = [[NSNumber alloc]init];
  self.progressBar = [[UIProgressView alloc]initWithProgressViewStyle:UIProgressViewStyleBar];
  self.progressBar.frame = CGRectMake(20, 240, 280, 40);
  [self.progressBar setProgress:0.0];
  self.theImageView = [[[UIImageView alloc]initWithFrame:[[UIScreen mainScreen]applicationFrame]]autorelease];
  self.theScrollView = [[[UIScrollView alloc]initWithFrame:[[UIScreen mainScreen]applicationFrame]]autorelease];
  self.theScrollView.delegate = self;
  [self.theScrollView addSubview:self.theImageView];
  self.view = self.theScrollView;
  self.theLabel = [[UILabel alloc]initWithFrame:CGRectMake(0, 200, 320, 40)];
  self.theLabel.font = [UIFont boldSystemFontOfSize:15.0f];
  self.theLabel.text = @"Please wait, file is being downloaded";
  self.theLabel.textAlignment = UITextAlignmentCenter;
  self.theLabel.hidden = NO;
  [self.view addSubview:self.progressBar];
  [self.view bringSubviewToFront:self.progressBar];
  [self.view addSubview:self.theLabel];
  [self.view bringSubviewToFront:self.    theLabel];
  [self performSelectorOnMainThread:@selector(setImageInImageView) withObject:nil waitUntilDone:NO];
}

And the header file:

@interface ImageViewerViewController : UIViewController

@property (nonatomic, retain) IBOutlet UIImageView *theImageView;
@property (nonatomic, retain) IBOutlet UIScrollView *theScrollView;
@property (nonatomic, retain) NSString *imageLink;
@property (nonatomic, retain) UIImage *theImage;
@property (nonatomic, retain) UILabel *theLabel;
@property (nonatomic, retain) UIProgressView *progressBar;
@property (nonatomic, retain) NSMutableData *resourceData;
@property (nonatomic, retain) NSNumber *filesize;
@end

Hope it helps