UIScrollView adjusts contentOffset when contentSiz

问题:

I am adjusting a detail view controller's state, just before it is pushed on a navigationController:

[self.detailViewController detailsForObject:someObject];
[self.navigationController pushViewController:self.detailViewController
                                     animated:YES];

In the DetailViewController a scrollView resides. Which content I resize based on the passed object:

- (void)detailsForObject:(id)someObject {
    // set some textView's content here
    self.contentView.frame = <rect with new calculated size>;

    self.scrollView.contentSize = self.contentView.frame.size;
    self.scrollView.contentOffset = CGPointZero;
}

Now, this all works, but the scrollView adjusts it's contentOffset during the navigationController's slide-in animation. The contentOffset will be set to the difference between the last contentSize and the new calculated one. This means that the second time you open the detailsView, the details will scroll to some unwanted location. Even though I'm setting the contentOffset to CGPointZero explicitly.

I found that resetting the contentOffset in - viewWillAppear has no effect. The best I could come up with is resetting the contentOffset in viewDidAppear, causing a noticeable up and down movement of the content:

- (void)viewDidAppear:(BOOL)animated {
    self.scrollView.contentOffset = CGPointZero;
}

Is there a way to prevent a UIScrollView from adjusting its contentOffset when its contentSize is changed?

回答1:

Occurs when pushing a UIViewController containing a UIScrollView using a UINavigationController.

iOS 7

Solution 1 (Code)

Set @property(nonatomic, assign) BOOL automaticallyAdjustsScrollViewInsets to NO.

Solution 2 (Storyboard)

Uncheck the Adjust Scroll View Insets

iOS 6

Solution (Code)

Set the UIScrollView's property contentOffset and contentInset in viewWillLayoutSubviews. Sample code:

- (void)viewWillLayoutSubviews{
  [super viewWillLayoutSubviews];
  self.scrollView.contentOffset = CGPointZero;
  self.scrollView.contentInset = UIEdgeInsetsZero;
}

回答2:

The cause of this problem remains unclear, though I've found a solution. By resetting the content size and offset before adjusting them, the UIScrollView won't animate:

- (void)detailsForObject:(id)someObject {
    // These 2 lines solve the issue:
    self.scrollView.contentSize = CGSizeZero;
    self.scrollView.contentOffset = CGPointZero;

    // set some textView's content here
    self.contentView.frame = <rect with new calculated size>;

    self.scrollView.contentSize = self.contentView.frame.size;
    self.scrollView.contentOffset = CGPointZero;
}

回答3:

I had the same issue with a UIScrollview, where the problem was caused by not setting the contentSize. After setting the contentSize to the number of items this problem was solved.

self.headerScrollView.mainScrollview.contentSize = CGSizeMake(320 * self.sortedMaterial.count, 0);

回答4:

Here's what worked for me:
In the storyboard, in the Size Inspector for the scrollView, set Content Insets Adjustment Behavior to "Never".

回答5:

Is your scrollView the root view of the DetailViewController? If yes, try wrapping the scrollView in a plain UIView and make the latter the root view of DetailViewController. Since UIViews don't have a contentOffset property, they are immune to content offset adjustments made by the navigation controller (due to the navigation bar, etc.).

回答6:

I experienced the problem, and for a specific case - I don't adjust the size - I used the following:

float position = 100.0;//for example

SmallScroll.center = CGPointMake(position + SmallScroll.frame.size.width / 2.0, SmallScroll.center.y);

Same would work with y: anotherPosition + SmallScroll.frame.size.height / 2.0

So if you don't need to resize, this is a quick and painless solution.

回答7:

I was experiencing a similar problem, where UIKit was setting the contentOffset of my scrollView during push animations.

None of these solutions were working for me, maybe because I was supporting iOS 10 and iOS 11.

I was able to fix my issue by subclassing my scrollview to keep UIKit from changing my offsets after the scrollview had been removed from the window:

/// A Scrollview that only allows the contentOffset to change while it is in the window hierarchy. This can keep UIKit from resetting the `contentOffset` during transitions, etc.
class LockingScrollView: UIScrollView {
    override var contentOffset: CGPoint {
        get {
            return super.contentOffset
        }
        set {
            if window != nil {
                super.contentOffset = newValue
            }
        }
    }
}