检查 UIScrollView 是否到达顶部或底部

Question

有没有办法知道 UIScrollView 是否到达顶部或底部？可能在方法中：

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView 
                  willDecelerate:(BOOL)decelerate

Answer 1

在您的类中实现UIScrollViewDelegate，然后添加以下内容：

-(void)scrollViewDidScroll: (UIScrollView*)scrollView
{
    float scrollViewHeight = scrollView.frame.size.height;
    float scrollContentSizeHeight = scrollView.contentSize.height;
    float scrollOffset = scrollView.contentOffset.y;

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

希望这就是您想要的！另外，还可以通过向上面的代码添加更多条件并 NSLog 记录scrollOffset 的值来进行修补。

Answer 2

好吧，当您尝试确定scrollView是在顶部还是在底部时，也涉及到contentInsets。您可能还对滚动视图位于顶部上方和底部下方的情况感兴趣。
这是我用来查找顶部和底部位置的代码：

Swift:

extension UIScrollView {

    var isAtTop: Bool {
        return contentOffset.y <= verticalOffsetForTop
    }

    var isAtBottom: Bool {
        return contentOffset.y >= verticalOffsetForBottom
    }

    var verticalOffsetForTop: CGFloat {
        let topInset = contentInset.top
        return -topInset
    }

    var verticalOffsetForBottom: CGFloat {
        let scrollViewHeight = bounds.height
        let scrollContentSizeHeight = contentSize.height
        let bottomInset = contentInset.bottom
        let scrollViewBottomOffset = scrollContentSizeHeight + bottomInset - scrollViewHeight
        return scrollViewBottomOffset
    }

}

Objective-C:

@implementation UIScrollView (Additions)

- (BOOL)isAtTop {
    return (self.contentOffset.y <= [self verticalOffsetForTop]);
}

- (BOOL)isAtBottom {
    return (self.contentOffset.y >= [self verticalOffsetForBottom]);
}

- (CGFloat)verticalOffsetForTop {
    CGFloat topInset = self.contentInset.top;
    return -topInset;
}

- (CGFloat)verticalOffsetForBottom {
    CGFloat scrollViewHeight = self.bounds.size.height;
    CGFloat scrollContentSizeHeight = self.contentSize.height;
    CGFloat bottomInset = self.contentInset.bottom;
    CGFloat scrollViewBottomOffset = scrollContentSizeHeight + bottomInset - scrollViewHeight;
    return scrollViewBottomOffset;
}


@end

Answer 3

如果你想要快速的代码：

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 4

简单干净的扩展：

import UIKit

extension UIScrollView {

    var scrolledToTop: Bool {
        let topEdge = 0 - contentInset.top
        return contentOffset.y <= topEdge
    }

    var scrolledToBottom: Bool {
        let bottomEdge = contentSize.height + contentInset.bottom - bounds.height
        return contentOffset.y >= bottomEdge
    }

}

在 GitHub 上：

https://github.com/salutis/swift-scroll -视图边缘

Answer 5

我确切地知道了该怎么做：

CGFloat maxPosition = scrollView.contentInset.top + scrollView.contentSize.height + scrollView.contentInset.bottom - scrollView.bounds.size.height;
CGFloat currentPosition = scrollView.contentOffset.y + self.topLayoutGuide.length;

if (currentPosition == maxPosition) {
  // you're at the bottom!
}

Answer 6

这样做（对于 Swift 3）：

class MyClass: UIScrollViewDelegate {

   func scrollViewDidScroll(_ scrollView: UIScrollView) {

        if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) {
           //scrolled to top, do smth
        }


    }
}