iphone - 检查 UIView 是否处于 UIScrollView 可见状态

Question

检查当前 UIScrollView 的 contentView 上是否可见 UIView 的最简单和最优雅的方法是什么？有两种方法，一种是涉及到 UIScrollView 的 contentOffset.y 位置，另一种是转换 rect 区域？

Answer 1

如果您正在尝试确定视图是否已在屏幕上滚动，请尝试以下操作：

    CGRect thePosition =  myView.frame;
    CGRect container = CGRectMake(scrollView.contentOffset.x, scrollView.contentOffset.y, scrollView.frame.size.width, scrollView.frame.size.height);
    if(CGRectIntersectsRect(thePosition, container))
    {
        // This view has been scrolled on screen
    }

Answer 2

Swift 5：如果您想触发一个事件来检查整个 UIView 在滚动视图中是否可见：

extension ViewController: UIScrollViewDelegate {

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if scrollView.bounds.contains(targetView.frame) {
            // entire UIView is visible in scroll view
        }
    }

}

Answer 3

在您的滚动视图委托中实现scrollViewDidScroll:并手动计算哪些视图是可见的（例如，通过检查是否CGRectIntersectsRect(scrollView.bounds, subview.frame)返回 true。

Answer 4

为 Swift 3 更新

var rect1: CGRect!
// initialize rect1 to the relevant subview
if rect1.frame.intersects(CGRect(origin: scrollView.contentOffset, size: scrollView.frame.size)) {
        // the view is visible
    }

Answer 5

我认为你的想法是正确的。如果是我，我会这样做：

//scrollView is the main scroll view
//mainview is scrollview.superview
//view is the view inside the scroll view

CGRect viewRect = view.frame;
CGRect mainRect = mainView.frame;

if(CGRectIntersectsRect(mainRect, viewRect))
{
    //view is visible
}

Answer 6

José 的解决方案对我来说不太奏效，它会在我的视图出现在屏幕上之前检测到它。如果 José 的简单解决方案不适合您，以下相交代码在我的 tableview 中完美运行。

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let viewFrame = scrollView.convert(targetView.bounds, from: targetView)
        if viewFrame.intersects(scrollView.bounds) {
            // targetView is visible 
        }
        else {
            // targetView is not visible
        }
    }

Answer 7

考虑插图的解决方案

public extension UIScrollView {
    
    /// Returns `adjustedContentInset` on iOS >= 11 and `contentInset` on iOS < 11.
    var fullContentInsets: UIEdgeInsets {
        if #available(iOS 11.0, *) {
            return adjustedContentInset
        } else {
            return contentInset
        }
    }

    /// Visible content frame. Equal to bounds without insets.
    var visibleContentFrame: CGRect {
        bounds.inset(by: fullContentInsets)
    }
}

if scrollView.visibleContentFrame.contains(view) {
    // View is fully visible even if there are overlaying views
}