Question

我有一个带图像的UIScrollView，当用户滚动到scrollview的末尾时，我想更新内容。这是我的代码，用于检测何时到达滚动视图的底部：

以下代码在scrollViewDidScroll:委托

中实施

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，我的函数会多次调用，但我想只调用一次。我尝试使用imagesScrollView.contentOffset.y == scrollViewBottomOffset但是它不起作用并且没有调用该函数

Answer 1

如果你想在swift中检测它们：

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。第一次调用方法时可能会更新它，也可能在用户向上滚动时更新它。

Answer 5

实施scrollViewDidScroll:并在其中检查contentOffset以达到目的

Answer 6

有时你必须在条件中使用+1，因为contentSize.height会给你一些小数，所以如果你使用它，你就可以避免它......

override func scrollViewDidScroll(scrollView: UIScrollView) {

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

Answer 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

为此我使用了混合方法。让我解释一下：

虽然您的微积分是正确的，但您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，它们在各自事件结束时仅被调用一次。

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
    }
}

检测UIScrollview底部到达

8 个答案: