iPhone - 知道UIScrollView是否达到顶部或底部

时间:2011-10-09 19:56:39

标签: ios objective-c iphone uiscrollview uiscrollviewdelegate

有没有办法知道UIScrollView是否已经到达顶部或底部

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

感谢。

6 个答案:

答案 0 :(得分:185)

在您的课程中实施UIScrollViewDelegate,然后添加:

-(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
    }
}

希望这就是你所追求的!否则,通过向上面的代码添加更多条件和NSLog scrollOffset的值来修改。

答案 1 :(得分:71)

当您尝试确定scrollView是在顶部还是在底部时,也会涉及contentInsets。当您的scrollView 位于顶部位于下方底部时,您可能也会感兴趣。 这是我用来查找顶部和底部位置的代码:

夫特:

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
    }

}

目标-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

答案 2 :(得分:27)

如果你想要swift中的代码:

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
    }
}

答案 3 :(得分:9)

简单而干净的扩展:

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-view-edges

答案 4 :(得分:4)

我弄明白该怎么做:

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!
}

答案 5 :(得分:0)

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
        }


    }
}