UICollectionView 自动滚动到 IndexPath 处的单元格 [英] UICollectionView auto scroll to cell at IndexPath

问题描述

在加载集合视图之前，用户设置集合视图数组中的图像数量.所有单元格都不适合屏幕.我有 30 个单元格，但屏幕上只有 6 个.

Before loading the collection view user sets the number of image in the array of collection view. All of the cells don't fit on the screen. I have 30 cells and only 6 on the screen.

问题:如何在加载 UICollectionView 时自动滚动到具有所需图像的单元格?

The question: How to scroll to the cell with desired image automatically at the load of UICollectionView?

推荐答案

我发现在 viewWillAppear 中滚动可能无法可靠地工作，因为集合视图尚未完成布局；您可能会滚动到错误的项目.

I've found that scrolling in viewWillAppear may not work reliably because the collection view hasn't finished it's layout yet; you may scroll to the wrong item.

我还发现在 viewDidAppear 中滚动会导致未滚动视图的瞬间闪烁可见.

I've also found that scrolling in viewDidAppear will cause a momentary flash of the unscrolled view to be visible.

而且，如果你每次都通过 viewDidLayoutSubviews 滚动，用户将无法手动滚动，因为某些集合布局在每次滚动时都会导致子视图布局.

And, if you scroll every time through viewDidLayoutSubviews, the user won't be able to manually scroll because some collection layouts cause subview layout every time you scroll.

以下是我发现的可靠方法:

Here's what I found works reliably:

目标 C:

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    // If we haven't done the initial scroll, do it once.
    if (!self.initialScrollDone) {
        self.initialScrollDone = YES;
    
        [self.collectionView scrollToItemAtIndexPath:self.myInitialIndexPath
                                    atScrollPosition:UICollectionViewScrollPositionRight animated:NO];
    }
}

斯威夫特:

 override func viewWillLayoutSubviews() {

    super.viewWillLayoutSubviews()

      if !self.initialScrollDone {

         self.initialScrollDone = true
         self.testNameCollectionView.scrollToItem(at:selectedIndexPath, at: .centeredHorizontally, animated: true)
    }

}

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