Change scrolling position of collection view, when view is currently not visible

问题

There are two scenarios where I have problem with setting the scrolling position of my collection view:

on start up I want to scroll to a certain item (starting position != beginning of the collection view)
view is currently not visible yet, but in "background" the collection view should scroll to a certain item

What is a reliable way to scroll the collection view to a certain cell? Currently I'm setting the scrolling position with scrollToItemAtIndexPath in viewDidAppear, but that is too late for me.

回答1:

Try to call the moethod in viewDidLayoutSubview:

Loooks like you cant scroll to item either in viewWillAppear/DidAppear!!!!

YOu can modify the UICollectionViewScrollPositionLeft based on your collection view scroll direction

-(void)viewDidLayoutSubviews{

    [super viewDidLayoutSubviews];

    NSIndexPath *indexPath=[NSIndexPath indexPathForItem:3 inSection:0]; //indexpath for the item to scroll

    [_collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];

}

Swift:

    func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    var indexPath: NSIndexPath = NSIndexPath.indexPathForItem(3, inSection: 0)
    collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .Left, animated: true)
}

The method viewDidLayoutSubviews will get called only once, and it doesnt get called based on the collection view scroll!!!

Normally it will get called after viewWillAppear and before viewDidAppear!!

回答2:

Try this:

CGPoint newContentOffset = yourCollectionView.contentOffset;
float offset = selectedIndex * (self.view.bounds.size.width + cellSpacing);
newContentOffset.x += offset;
yourCollectionView.contentOffset = newContentOffset;

来源：https://stackoverflow.com/questions/33737839/change-scrolling-position-of-collection-view-when-view-is-currently-not-visible

标签

ios

uiscrollview

uicollectionview