Flex:确定组件是否显示 [英] Flex: Determine if a component is showing

问题描述

确定 Flex/Flash 中的组件是否显示在用户屏幕上的最佳方法是什么?我正在寻找类似于 Java 的 Component.isShowing() 方法.

What is the best way to determine if a component in Flex/Flash is showing on the user's screen? I'm looking for an analog to Java's Component.isShowing() method.

show 和 hide 事件触发可见性，这似乎适用于 ViewStack 组件的第一个后代，但不适用于显示树.

The show and hide events fire for visibility, and this seems to work for the first descendant of a ViewStack component, but not further down the display tree.

推荐答案

UIComponent.visible 不一定对可见=false 的对象的子级有效.来自文档:

UIComponent.visible is not necessarily valid for children of an object where visible=false. From the docs:

在任何一种情况下，对象的子对象都不会发出显示或隐藏事件，除非对象专门编写了一个实现来这样做."

"In either case the children of the object will not emit a show or hide event unless the object has specifically written an implementation to do so."

我编写了一个示例应用程序来证实这是真的.您可以做的是在显示列表中检查可见性是否在父项上为假.基本上可见"会给出误报，但不应该给出误报.这是我整理的一个快速实用程序:

I wrote a sample application that confirms this to be true. What you can do is walk up the display list checking for visible to be false on a parent. Basically "visible" gives false positives but shouldn't give false negatives. Here is a quick utility I put together:

package
{
    import flash.display.DisplayObject;

    import mx.core.Application;

    public class VisibilityUtils
    {
        public static function isDisplayObjectVisible(obj : DisplayObject) : Boolean {
            if (!obj.visible) return false;
            return checkDisplayObjectVisible(obj);
        }

        private static function checkDisplayObjectVisible(obj : DisplayObject) : Boolean {
            if (!obj.parent.visible) return false;
            if (obj.parent != null && !(obj.parent is Application))
                return checkDisplayObjectVisible(obj.parent);
            else
                return true;
        }
    }
}

除了简单的测试之外，我还没有做过任何其他事情，但它应该可以帮助您入门.

I haven't done anything more than trivial tests on this but it should get you started.

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