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

问题描述

在加载收集视图之前，用户设置收集视图数组中的图像数.屏幕上没有所有的单元格.我有30个单元格，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其布局.您可能滚动到错误的项目.

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时闪烁可见.

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

并且，如果您每次在viewDidLayoutSubviews中滚动，则用户将无法手动滚动，因为某些集合布局会在您每次滚动时导致子视图布局.

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.

这是我发现可靠工作的地方:

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];
    }
}

迅速:

 override func viewWillLayoutSubviews() {

    super.viewWillLayoutSubviews()

      if (!self.initialScrollDone) {

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

}

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