问题描述

我正在尝试在 iOS 5 中使用新的 scrollViewWillEndDragging:withVelocity:targetContentOffset: UIScrollView 委托调用，但我似乎无法让它真正正确地响应我.我正在更改 targetContentOffset->x 值，但它永远不会被使用.我知道代码正在运行，因为它会在该函数中遇到断点.我什至尝试将偏移值设置为硬编码数字，这样我就知道它会在哪里结束，但它永远不会起作用.

I'm trying to use the new scrollViewWillEndDragging:withVelocity:targetContentOffset: UIScrollView delegate call in iOS 5 but i can't seem to get it to actually respond to me correctly. I'm changing the targetContentOffset->x value but it never ends up being used. I know the code is being ran because it'll hit breakpoints in that function. I've even tried setting the offset value to a hard coded number so i'd know where it would end up but it never works.

有没有人能够正确使用它并使其工作?是否有任何其他必须实现的委托调用才能使其工作?

Has anyone been able to use this correctly and make it work? Is there any other delegate call that must be implemented in order for this to work?

这是我的代码，以防有人发现它有问题:

Here's my code in case someone sees something wrong with it:

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    // goodOffsetX returns the contentOffset i want the scrollView to stop at
    CGFloat goodOffsetX = [self _horizontalContentOffsetForTargetHorizontalContentOffset:(*targetContentOffset).x velocity:velocity.x];

    NSLog( @" " );
    NSLog( @"scrollViewWillEndDragging" );
    NSLog( @"   velocity: %f", velocity.x );
    NSLog( @"   currentX: %f", scrollView.contentOffset.x );
    NSLog( @"   uikit targetX: %f", (*targetContentOffset).x );
    NSLog( @"   pagedX: %f", goodOffsetX );

    targetContentOffset->x = goodOffsetX; 
}

推荐答案

您可以使用此代码实现自定义分页:

You can implement custom paging with this code:

- (float) pageWidth {
    return ((UICollectionViewFlowLayout*)self.collectionView.collectionViewLayout).itemSize.width +
    ((UICollectionViewFlowLayout*)self.collectionView.collectionViewLayout).minimumInteritemSpacing;
}

- (void) scrollViewWillBeginDragging:(UIScrollView *)scrollView {

    CGFloat pageWidth = self.collectionView.frame.size.width + 10 /* Optional Photo app like gap between images. Or use [self pageWidth] in case if you want the next page be also visible */;

    _currentPage = floor((self.collectionView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;

    NSLog(@"Dragging - You are now on page %i", _currentPage);
}

- (void) scrollViewWillEndDragging:(UIScrollView*)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint*)targetContentOffset {

    CGFloat pageWidth = self.collectionView.frame.size.width + 10; // [self pageWidth]

    int newPage = _currentPage;

    if (velocity.x == 0) { // slow dragging not lifting finger
        newPage = floor((targetContentOffset->x - pageWidth / 2) / pageWidth) + 1;
    }
    else {
        newPage = velocity.x > 0 ? _currentPage + 1 : _currentPage - 1;

        if (newPage < 0)
            newPage = 0;
        if (newPage > self.collectionView.contentSize.width / pageWidth)
            newPage = ceil(self.collectionView.contentSize.width / pageWidth) - 1.0;
    }

    NSLog(@"Dragging - You will be on %i page (from page %i)", newPage, _currentPage);

    *targetContentOffset = CGPointMake(newPage * pageWidth, targetContentOffset->y);
}

当然你必须设置 pagingEnabled = NO._currentPage 是一个类 iVar.感谢 http://www.mysamplecode.com/2012/12/ios-scrollview-example-with-paging.html 用于指出正确的方式.

Of course you must set pagingEnabled = NO. _currentPage is a class iVar. Thanks to http://www.mysamplecode.com/2012/12/ios-scrollview-example-with-paging.html for pointing the right way.

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