UICollectionView使边界更改上的布局无效 [英] UICollectionView Invalidate Layout On Bounds Changes

问题描述

我目前有以下代码片段用于计算 UICollectionViewCells 尺寸：

I currently have the following snippet for calculating UICollectionViewCells sizes:

- (CGSize)collectionView:(UICollectionView *)mainCollectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)atIndexPath
{
    CGSize bounds = mainCollectionView.bounds.size;
    bounds.height /= 4;
    bounds.width /= 4;
    return bounds;
}

这是有效的。但是，我现在在 viewDidLoad 中添加一个键盘观察器（它触发 UICollectionView的委托和数据源方法在它出现之前并从故事板中调整自己的大小）。因此，界限是错误的。我也想支持轮换。如果 UICollectionView 改变大小，那么处理这两个边缘情况并重新计算大小的好方法是什么？

This works. However, I'm now adding a keyboard observer in viewDidLoad (which is triggering the the delegate and data source methods for the UICollectionView before it appears and resizes itself from the storyboard). The bounds are thus wrong. I also would like to support rotation. What's a good way of handling these two edge cases and re-calculating the sizes if the UICollectionView changes size?

推荐答案

当集合视图的边界发生变化时，使布局无效的解决方案是覆盖 shouldInvalidateLayoutForBoundsChange：并返回是。
它也在文档中说明： https://developer.apple。 com / documentation / uikit / uicollectionviewlayout / 1617781-shouldinvalidatelayoutforboundsc

The solution for invalidating your layout when the bounds of the collection view changes is to override shouldInvalidateLayoutForBoundsChange: and return YES. It's also stated in the documentation: https://developer.apple.com/documentation/uikit/uicollectionviewlayout/1617781-shouldinvalidatelayoutforboundsc

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds 
{
     return YES;
}

这也应包括轮换支持。如果没有，请实现 viewWillTransitionToSize：withTransitionCoordinator：

This should cover rotation support as well. If it doesn't, implement viewWillTransitionToSize:withTransitionCoordinator:

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
    [super viewWillTransitionToSize:size
          withTransitionCoordinator:coordinator];

    [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context)
     {
         [self.collectionView.collectionViewLayout invalidateLayout];
     }
                                 completion:^(id<UIViewControllerTransitionCoordinatorContext> context)
     {
     }];
}

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