檢測到 UIScrollview 底部

Question

我有一個帶有圖像的 UIScrollView，當用戶滾動到滾動視圖的末尾時，我想更新內容。 這是我檢測何時到達滾動視圖底部的代碼：

下面的代碼在scrollViewDidScroll: delegate 中實現

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];

}

我的問題是，當用戶滾動到底部時，我的函數被調用了幾次，但我只想調用它一次。 我嘗試使用 imagesScrollView.contentOffset.y == scrollViewBottomOffset 但它不起作用並且未調用該函數

Answer 1

如果您想快速檢測它們：

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。

對於 Swift 4.x，您必須更改方法名稱：

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

你有沒有想過添加一個布爾值。 在第一次調用該方法時更新它，也許當用戶向上滾動時更新它。

Answer 5

有時您將不得不在條件中使用 +1，因為 contentSize.height 給了您幾個小數，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

實現scrollViewDidScroll:並檢查contentOffset以達到終點

Answer 7

對於 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

我為此使用了混合方法。 讓我解釋：

雖然您的微積分是正確的，但您收聽的委托是一種矯枉過正，因為scrollViewDidScroll被多次調用，這可能會導致性能問題。 您應該（像我一樣）使用scrollViewDidEndDragging和scrollViewDidEndDecelerating ，它們僅在每個事件結束時調用一次。

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
}}

確保您的視圖實現了 UIScrollViewDelegate

MyView: UITableViewDelegate,UIScrollViewDelegate