如果QML组件是从C＆＃x2B;＆＃x2B;

Question

我的目标是创建一个自定义组件（让我们称其为componentloader），该组件可以通过委托来实例化另一个组件（我们称其为delegatecomponent）。

问题在于，创建后未显示delegatecompont的实例（白屏幕）。注意：tst_component已加载消息存在，这意味着delegatecomponent实例实际创建了。

这是一个最小示例：

main.qml

ApplicationWindow {
    id: mainWindow
    width: 640
    height: 480
    visible: true

    Component {
        id: tst_component

        Rectangle {
            anchors.fill: parent

            Component.onCompleted: {
                console.debug("tst_component is loaded");
            }

            Label {
                text: "hello world"
                anchors.centerIn: parent
            }
        }
    }

// doesn't work
    ComponentLoader {
        anchors.fill: parent
        delegate: tst_component
    }

// works
//    Loader {
//        anchors.fill: parent
//        sourceComponent: tst_component
//    }
}

componentloader.h + componentloader.cpp

#pragma once
#include <QQuickItem>

class ComponentLoader : public QQuickItem
{
    Q_OBJECT
    Q_PROPERTY(QQmlComponent* delegate READ delegate WRITE setDelegate NOTIFY delegateChanged)

public:
    QQmlComponent* delegate() const;
    void setDelegate(QQmlComponent*);

signals:
    void delegateChanged();

private:
    void generate();

protected:
    void componentComplete() override;

private:
    QQmlComponent* mDelegate = nullptr;
};

// componentloader.cpp
#include "componentloader.h"
#include <QtWidgets/QtWidgets>
#include <QtQmlModels/QtQmlModels>
#include <QQuickWindow>

QQmlComponent* ComponentLoader::delegate() const
{
    return mDelegate;
}

void ComponentLoader::setDelegate(QQmlComponent* delegate)
{
    if (delegate != mDelegate)
    {
        mDelegate = delegate;
        emit delegateChanged();
    }
}

void ComponentLoader::componentComplete()
{
    QQuickItem::componentComplete();
    generate();
}

void ComponentLoader::generate()
{
    QQmlEngine* engine = qmlEngine(this);
    QQmlContext* root_ctx = engine->rootContext();
    QQmlContext* ctx = new QQmlContext(root_ctx);

    QObject* item = mDelegate->create(ctx);
    QQuickItem* quickItem = qobject_cast<QQuickItem*>(item);

    QQuickItem* quickParent = qobject_cast<QQuickItem*>(parent());
    quickItem->setParent(quickParent);
    quickItem->setParentItem(quickParent);
}

Answer 1

您的QuickParent指针将qobject parent（）值而不是qquickitem parentItem（）值。

当我尝试您的代码时，只需将其更改为对我来说有用：

QQuickItem* quickParent = qobject_cast<QQuickItem*>(parentItem());

我也认为您根本不需要致电SetParent（）。只是setParentItem（）。