ios - 使用 scrollViewWillEndDragging 自定义 UIScrollView 分页

Question

我正在尝试在 iOS 5 中使用新的 scrollViewWillEndDragging:withVelocity:targetContentOffset: UIScrollView 委托(delegate)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，这样我就知道它最终会在哪里，但它永远不会起作用。

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

这是我的代码，以防有人发现它有问题:

- (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; 
}

Answer 1

您可以使用此代码实现自定义分页:

- (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 iVar 类。感谢http://www.mysamplecode.com/2012/12/ios-scrollview-example-with-paging.html指出正确的方法。