销毁设置为 ShaderEffectSource 的 sourceItem 的 Item 也会隐藏 ShaderEffectSource

问题描述

简而言之，我在做什么:

What I'm doing, in short:

• 我有一个 ShaderEffectSource 项目，名为 snapshotItem，带有 live: false
• 动态实例化一个名为 dynamicItem
的项目
• 设置snapshotItem.sourceItem = dynamicItem
• 调用snapshotItem.scheduleUpdate()
• 此时，我成功地在屏幕上看到了 dynamicItem 的两个副本
• 在任意键上，我:
  • 将 snapshotItem.sourceItem 设置为一个空的、虚拟的 Item，以减少下一步出现问题的可能性
  • 销毁dynamicItem
  • I have a ShaderEffectSource Item named snapshotItem with live: false
  • Dynamically instantiating an Item called dynamicItem
  • Setting snapshotItem.sourceItem = dynamicItem
  • Calling snapshotItem.scheduleUpdate()
  • At this point, I successfully see two copies of dynamicItem on screen
  • On any key, I:
    • set snapshotItem.sourceItem to an empty, dummy Item, to make the next step less likely to cause problems
    • destroy dynamicItem

    问题是，当按下一个键时，两个副本都会从屏幕上消失，而我希望 snapshotItem 保留其中一个.

    The problem is that when a key is pressed, both copies disappear from screen, when I want the snapshotItem one to remain.

    注意:如果您对实现这一目标的动机感兴趣，请参阅我之前的问题一>.

    Note: If you're interested in the motivation behind wanting to achieve this, see my previous question.

    我的代码:

    import QtQuick 2.6
    import QtQuick.Window 2.2
    
    Window {
        visible: true
        width: 640
        height: 480
    
        property int childWidth: 100
        property int childHeight: 100
    
        id: root
        property var dynamicItem
    
        Item {
            id: dummy
        }
    
        Component {
            id: dynamicItemComponent
            Rectangle {
                color: "red"
            }
        }
    
        Component.onCompleted: {
            dynamicItem = dynamicItemComponent.createObject(row);
            dynamicItem.width = childWidth;
            dynamicItem.height = childHeight;
            snapshotItem.sourceItem = dynamicItem;
            snapshotItem.scheduleUpdate();
        }
    
        Item {
            focus: true
            Keys.onPressed: {
                snapshotItem.sourceItem = dummy;
                dynamicItem.destroy();
            }
        }
    
        Row {
            id: row
            spacing: 10
            ShaderEffectSource {
                id: snapshotItem
                live: false
                width: childWidth
                height: childHeight
            }
        }
    }
    

    推荐答案

    您不需要使用 dummyItem.您可以将 sourceItem 设置为 ShaderEffectSource 本身.

    You don't need to use a dummyItem. You can set the sourceItem to the ShaderEffectSource itself.

    也许你应该将 recursive 设置为 true，但没有它也能工作.

    Maybe you should set recursive to true, but it also works without it.

    import QtQuick 2.6
    import QtQuick.Window 2.2
    
    Window {
        visible: true
        width: 640
        height: 480
    
        property int childWidth: 100
        property int childHeight: 100
    
        id: root
        property var dynamicItem
    
        Component {
            id: dynamicItemComponent
            Rectangle {
                color: "red"
            }
        }
    
        Component.onCompleted: {
            dynamicItem = dynamicItemComponent.createObject(row);
            dynamicItem.width = childWidth;
            dynamicItem.height = childHeight;
            snapshotItem.sourceItem = dynamicItem;
            snapshotItem.scheduleUpdate();
        }
    
        Item {
            focus: true
            Keys.onPressed: {
                snapshotItem.sourceItem = snapshotItem;
                dynamicItem.destroy();
            }
        }
    
        Row {
            id: row
            spacing: 10
            ShaderEffectSource {
                id: snapshotItem
                live: false
                // recursive: sourceItem === this
                width: childWidth
                height: childHeight
            }
        }
    }
    

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