检测到 UIScrollview 底部

Question

我有一个带有图像的 UIScrollView，当用户滚动到滚动视图的末尾时，我想更新内容。 这是我检测何时到达滚动视图底部的代码：

下面的代码在scrollViewDidScroll: delegate 中实现

CGFloat scrollViewHeight = imagesScrollView.bounds.size.height;
CGFloat scrollContentSizeHeight = imagesScrollView.contentSize.height;
CGFloat bottomInset = imagesScrollView.contentInset.bottom;
CGFloat scrollViewBottomOffset = scrollContentSizeHeight + bottomInset - scrollViewHeight;

if(imagesScrollView.contentOffset.y > scrollViewBottomOffset){


    [imagesView addSubview:imagesBottomLoadingView];

    [self downloadImages];

}

我的问题是，当用户滚动到底部时，我的函数被调用了几次，但我只想调用它一次。 我尝试使用 imagesScrollView.contentOffset.y == scrollViewBottomOffset 但它不起作用并且未调用该函数

Answer 1

如果您想快速检测它们：

override func scrollViewDidScroll(scrollView: UIScrollView) {

if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) {
    //reach bottom
}

if (scrollView.contentOffset.y < 0){
    //reach top
}

if (scrollView.contentOffset.y >= 0 && scrollView.contentOffset.y < (scrollView.contentSize.height - scrollView.frame.size.height)){
    //not top and not bottom
}}

Answer 2

卡洛斯的回答更好。

对于 Swift 4.x，您必须更改方法名称：

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if (scrollView.contentOffset.y + 1) >= (scrollView.contentSize.height - scrollView.frame.size.height) {
            //bottom reached
        }
    }

Answer 3

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView 
{
    float bottomEdge = scrollView.contentOffset.y + scrollView.frame.size.height;
    if (bottomEdge >= scrollView.contentSize.height) 
    {
        // we are at the end
    }
}

Answer 4

你有没有想过添加一个布尔值。 在第一次调用该方法时更新它，也许当用户向上滚动时更新它。

Answer 5

有时您将不得不在条件中使用 +1，因为 contentSize.height 给了您几个小数，所以如果您使用它，您可以避免它......

override func scrollViewDidScroll(scrollView: UIScrollView) {

   if (scrollView.contentOffset.y + 1) >= (scrollView.contentSize.height - scrollView.frame.size.height) {
       //bottom reached
   }
}

Answer 6

实现scrollViewDidScroll:并检查contentOffset以达到终点

Answer 7

对于 Swift 4.5：

func scrollViewDidScroll(_ scrollView: UIScrollView) 
{    
   let scrollViewHeight = scrollView.frame.size.height
    let scrollContentSizeHeight = scrollView.contentSize.height
     let scrollOffset = scrollView.contentOffset.y

    if (scrollOffset == 0)
    {
        // then we are at the top
        print("then we are at the top")
    }
    else if (scrollOffset + scrollViewHeight == scrollContentSizeHeight)
    {
        print("then we are at the end")
        // then we are at the end
    }      
}

Answer 8

我为此使用了混合方法。 让我解释：

虽然您的微积分是正确的，但您收听的委托是一种矫枉过正，因为scrollViewDidScroll被多次调用，这可能会导致性能问题。 您应该（像我一样）使用scrollViewDidEndDragging和scrollViewDidEndDecelerating ，它们仅在每个事件结束时调用一次。

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    // Scrolling acceleration didn't continue after the finger was lifted
    if !decelerate {
        executeActionAtTheEnd(of: scrollView)
    }
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    executeActionAtTheEnd(of: scrollView)
}

private func executeActionAtTheEnd(of scrollView: UIScrollView) {
    if scrollView.contentOffset.y + 1 >= (scrollView.contentSize.height - scrollView.frame.size.height) {
        // Do here whatever you want when end of scrolling is reached
    }
}

Answer 9

func scrollViewDidEndDecelerating(scrollView: UIScrollView) {

if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) {
    //reach bottom
}

if (scrollView.contentOffset.y <= 0){
    //reach top
}

if (scrollView.contentOffset.y >= 0 && scrollView.contentOffset.y < (scrollView.contentSize.height - scrollView.frame.size.height)){
    //not top and not bottom
}}

确保您的视图实现了 UIScrollViewDelegate

MyView: UITableViewDelegate,UIScrollViewDelegate