Iphone – Scrolling, zooming UIScrollView and interface orientation rotation. How to use autoresize and more

autoresizeiphonelandscapeuiscrollviewzooming

This should be a pretty common thing to do, but I haven't been able to get it to work exactly right.

I have rectangular content. It normally fits in 320×361: portrait mode minus status bar minus ad minus tab bar.

I have put that content in a UIScrollView and enabled zooming. I also want interface rotation to work. The content will always be a tall rectangle, but when zoomed users might want to see more width at a time and less height.

What do I need to do in Interface Builder and code to get this done? How should I set my autoresizing on the different views? How do I set my contentSize and contentInsets?

I have tried a ton of different ways and nothing works exactly right. In various of my solutions, I've had problems with after some combination of zooming, interface rotation, and maybe scrolling, it's no longer possible to scroll to the entire content on the screen. Before you can see the edge of the content, the scroll view springs you back.

The way I'm doing it now is about 80% right. That is, out of 10 things it should do, it does 8 of them. The two things it does wrong are:

  1. When zoomed in portrait mode, you can scroll past the edge of the content, and see a black background. That's not too much to complain about. At least you can see all the content. In landscape mode, zoomed or not, seeing the black background past the edge is normal, since the content doesn't have enough width to fill the screen at 1:1 zoom level (the minimum).

  2. I am still getting content stuck off the edge when it runs on a test device running iOS 3.0, but it works on mine running 4.x. — Actually that was with the previous solution. My tester hasn't tried the latest solution.

Here is the solution I'm currently using. To summarize, I have made the scroll view as wide and tall as it needs to be for either orientation, since I've found resizing it either manually or automatically adds complexity and is fragile.

View hierarchy:

  • view
    • scrollView
      • scrollableArea
        • content
    • ad

view is 320×411 and has all the autoresizing options on, so conforms to screen shape

scrollView is 480 x 361, starts at origin -80,0, and locks to top only and disables stretching

scrollableArea is 480 x 361 and locks to left and top. Since scrollView disables stretching, the autoresizing masks for its subviews don't matter, but I tell you anyway.

content is 320×361, starts at origin 80,0, and locks to top

I am setting scrollView.contentSize to 480×361.

shouldAutorotateToInterfaceOrientation supports all orientations except portrait upside down.

In didRotateFromInterfaceOrientation, I am setting a bottom content inset of 160 if the orientation is landscape, resetting to 0 if not. I am setting left and right indicator insets of 80 each if the orientation is portrait, resetting if not.

scrollView.minimumZoomScale = 1.0

scrollView.maximumZoomScale = 2.0

viewForZoomingInScrollView returns scrollableArea

Best Answer

// in IB it would be all options activated
scrollView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
scrollView.contentSize = content.frame.size; // or bounds, try both

what do you mean with scrollableArea?

your minZoomScale is set to 1.0 thats fine for portrait mode but not for landscape. Because in landscape your height is smaller than in portrait you need to have a value smaller than 1.0. For me I use this implementation and call it every time, the frame of the scrollView did change:

- (void)setMaxMinZoomScalesForCurrentBounds {
    CGSize boundsSize = self.bounds.size; // self is a UIScrollView here
    CGSize contentSize = content.bounds.size;

    CGFloat xScale = boundsSize.width / contentSize.width;
    CGFloat yScale = boundsSize.height / contentSize.height;
    CGFloat minScale = MIN(xScale, yScale);

    if (self.zoomScale < minScale) {
        [self setZoomScale:minScale animated:NO];
    }
    if (minScale<self.maximumZoomScale) self.minimumZoomScale = minScale;
    //[self setZoomScale:minScale animated:YES];
}

- (void)setFrame:(CGRect)rect { // again, this class is a UIScrollView
    [super setFrame:rect];
    [self setMaxMinZoomScalesForCurrentBounds];
}
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