Question

I am new to iPhone developer,

I want scrolling in my Image,

Here is my code snippet,

- (void)viewDidLoad {
UIImage *image1 = [UIImage imageWithContentsOfFile:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bg.png"]];
    self.imageView = [[UIImageView alloc] initWithImage:image1];
    self.imageView.frame = (CGRect){.origin=CGPointMake(0.0f, 0.0f), .size=image1.size};
    [self.scrollView addSubview:self.imageView];
    self.scrollView.contentSize = image.size;

 [self centerScrollViewContents];
}


- (void)centerScrollViewContents {
    CGSize boundsSize = self.scrollView.bounds.size;
    CGRect contentsFrame = self.imageView.frame;

    if (contentsFrame.size.width < boundsSize.width) {
        contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0f;
    } else {
        contentsFrame.origin.x = 0.0f;
    }

    if (contentsFrame.size.height < boundsSize.height) {
        contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0f;
    } else {
        contentsFrame.origin.y = 0.0f;
    }

    self.imageView.frame = contentsFrame;
}

- (UIView*)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    // Return the view that you want to zoom
    return self.imageView;
}

also bg.png is not getting applied to my background.

Any help will be appreciated.

Answer 1

the answer is actually a combination of many of the other answers & comments, plus some other adjustments.

1. as Pan said, you need to set your scrollView delegate. otherwise, your
   viewForZoomingInScrollView: delegate implementation won’t get called.
   i’ve provided this call in viewDidLoad: , though you can also hook this
   up in interface builder or storyboard.
2. as Teodor Carstea said in the comments to the original post, in your
   original code, you are setting your .imageView.size and your
   .scrollView.contentsSize to exactly the same thing. you don’t need
   the code that sets the .imageView.frame. that will happen as part of
   initWithImage: . and this will make the sizes different.
3. you do need to set the .scrollView.contentSize to the image.size .
   it sort of matters where ou do this, at least in terms of that it must
   happen prior to setting the zoom scale.
4. as Kunal Balani mentioned, you have to have scrollingEnabled, though you
   can set this in storyboard or interface builder.
5. as MidhunMP said, you have to have .userInteractionEnabled = YES, though
   generally, these are the defaults that get set in storyboard/Interface Builder,
   so i’m not going to include them in the code changes below.
6. your method centerScrollViewContents isn’t really centering the contents
   as much as it is re-shaping the imageView frame. i’ve simply commented out
   the call, because i think it’s completely unnecessary. instead, i’ve made
   a simple call to start your image in the upper left corner.
7. if you only want to scroll, setting the zoomScale, minimumZoomScale and
   maximumZoomScale is not necessary. if you also want to pinch-zoom, then
   you will need to set all three of these, and in the proper places.
8. you do seem to want to stretch the view if it is smaller than the content
   bounds. if this is truly a concern (i.e. if you know your bg.png is so
   small that it needs to be stretched), then calculate the contentFrame to
   image frame width ratio and height ratio separately, and whichever of
   these is larger will be your new zoomScale, and you’ll be able to scroll
   in the other direction. or, there are other ways to decide how you want
   that scale set. search stackoverflow.com for other answers for setting
   the zoom scale as desired.

here’s the code after applying these items.

(void)viewDidLoad {
    self.scrollView.delegate = self;         // can be set in storyboard
    self.scrollView.scrollingEnabled = YES;  // can be set in storyboard
    NSString* bgPng
      = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bg.png"];
    UIImage *image1 = [UIImage imageWithContentsOfFile:bgPng];
    self.imageView = [[UIImageView alloc] initWithImage:image1];
//  self.imageView.frame = (CGRect){.origin=CGPointMake(0.0f, 0.0f), .size=image1.size};
    [self.scrollView addSubview:self.imageView];
    self.scrollView.contentSize = image.size;

    // set zoom scale here if desired.

    // if zoom is implemented, the following call should be made
    // after setting .zoomScale, .minimumZoomScale & .maximumZoomScale
    self.scrollView.contentOffset = CGPointZero;

//  [self centerScrollViewContents];
}


//- (void)centerScrollViewContents {
//    CGSize boundsSize = self.scrollView.bounds.size;
//    CGRect contentsFrame = self.imageView.frame;
//
//    if (contentsFrame.size.width < boundsSize.width) {
//        contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0f;
//    } else {
//        contentsFrame.origin.x = 0.0f;
//    }
//
//    if (contentsFrame.size.height < boundsSize.height) {
//        contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0f;
//    } else {
//        contentsFrame.origin.y = 0.0f;
//    }
//  
//    self.imageView.frame = contentsFrame;
//}

- (UIView*)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    // Return the view that you want to zoom
    return self.imageView;
}