Question

我有多个UIVIew子视图的UIScrollView。我想更新每个UIView出现在UIScrollView可见部分时显示的数据。

触发的回调是什么？我试过了viewWillAppear，但它似乎没有被调用。

感谢。：）

Answer 1

您必须自己进行计算。在滚动视图委托中实施scrollViewDidScroll:并手动计算哪些视图可见（例如，通过检查CGRectIntersectsRect(scrollView.bounds, subview.frame)是否返回true。

Answer 2

Swift 3解决方案

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let viewFrame = greenView.frame

    let container = CGRect(x: scrollView.contentOffset.x, y: scrollView.contentOffset.y, width: scrollView.frame.size.width, height: scrollView.frame.size.height)


    // We may have received messages while this tableview is offscreen
    if (viewFrame.intersects(container)) {
        // Do work here
        print("view is visible")
    }
    else{
        print("nope view is not on the screen")
    }
}

Answer 3

如果您的滚动视图未处于放大状态，则上述答案是正确的。万一你的滚动视图可以放大以上计算，因为你需要考虑缩放

这是代码

auto animation = Animation::createWithSpriteFrames(animFrames, 0.2f);
auto animate = Animate::create(animation);
sprite->runAction(animate);

Answer 4

略微改进。我想知道滚动视图中显示的视图数量：

editor.on("beforeEndOperation", function(e) {
    if (editor.curOp.docChanged && editor.curOp.command.name == "insertstring") {
        var pos = editor.getCursorPosition();
        var token = editor.session.getTokenAt(pos.row, pos.column);
        if (token && token.type == "keyword") {
            alert(
                "Hey there!", 
                "This is me, the most annoying editor feature evar.",
                "Just wanted to let you know, that you have typed a keyword",
                token.value
            );
        }
    }
});

Answer 5

Ole Begemann的迅速回答5，

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if scrollView.bounds.intersects(subViewFrame){
            // do something
        }
}

注意：请确保subViewFrame是相对于scrollView的框架计算的。

viewWillAppear用于子视图

5 个答案: