How to properly replace image in UIImageView in UIScrollView on iOS

Question

I have an interesting problem. I have one UIScrollView and inside only one UIImageView with image. I need this for zooming and panning. Ok. On a button touch I want to replace image within UIImageView (which is within UIScrollView, like a mentioned) with the next one in line.

So far I've done this like that:

self.imageView = nil;
self.imageView = [[UIImageView alloc] initWithImage:nextImage];

The reason that I always set self.imageView to nil is that if I don't do that than the next image is scaled or zoomed like the previous one was.

But I don't think thats fine solution for memory efficiency.

Is there any other way to set new image on UIImageView with "reset" option for zooming, scale, etc... ?

UPDATE: The code that still does not work:

[self.scrollView setZoomScale:1.0];
[self.imageView setImage:photoImage];
[self.imageView setFrame:rect];
[self.scrollView setContentSize:[self.imageView frame].size];
CGFloat minZoomScale = [self.scrollView frame].size.width / [self.imageView frame].size.width;
if (minZoomScale < [self.scrollView frame].size.height / [self.imageView frame].size.height) {
    minZoomScale = [self.scrollView frame].size.height / [self.imageView frame].size.height;
}
[self.scrollView setMinimumZoomScale:minZoomScale];
[self.scrollView setZoomScale:[self.scrollView minimumZoomScale]];

UPDATE 2 Just figured out what I was doing wrong. I did not reset the minimum zoom scale.

[self.scrollView setMinimumZoomScale:1.0];

Now it works!

Answer 1

There is a property called zoomScale in UIScrollView

Set 1.0 to the zoomScale of your scrollview. No need to release the old UIImageView and to allocate a new UIImageView everytime. You can directly set the image to the imageview and set the zoomScale of the UIScrollView to 1.0.

Answer 2

Just want to make one thing clear because I ran into the same problem: reset the minimum zoom scale to 1.0 BEFORE changing the image of the imageView:

[self.scrollView setMinimumZoomScale:1.0];
[self.scrollView setZoomScale:1.0];
[self.imageView setImage:photoImage];
[self.photoView setFrame:(CGRect){.origin=CGPointMake(0.0f, 0.0f), photoImage.size=photo.size}];
[self.scrollView setContentSize:[self.imageView frame].size];
CGFloat minZoomScale = MIN([self.scrollView frame].size.width / [self.imageView frame].size.width,  [self.scrollView frame].size.height / [self.imageView frame].size.height)
[self.scrollView setMinimumZoomScale:minZoomScale];
[self.scrollView setMaximumZoomScale:1.0];
[self.scrollView setZoomScale:[self.scrollView minimumZoomScale]];
[self centerScrollViewContents];

and for centring the image:

- (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;
}