Qt:如何在 C++ 端而不是 QML 监控 Q_PROPERTY 更改 [英] Qt : How to monitor a Q_PROPERTY change on C++ side instead of QML

问题描述

我使用的是 Qt 5.9.3.我在我的应用程序的 main.qml

中声明了以下属性

代码:

//main.qml我的快速项目{属性颜色 nextColoronNextColorChanged:{console.log("下一个颜色是:" + nextColor.toString())}}//MyQuickItem.h类 MyQuickItem : 公共 QQuickItem {}

问题:

如何在C++端定义onNextColorChanged?

我知道我也可以将 nextColor 作为 C++ 类 MyQuickItem 中的一个属性.像这样

//MyQuickItem.h类 MyQuickItem : 公共 QQuickItem {Q_PROPERTY(QColor nextColor READ nextColor WRITE setNextColor NOTIFY nextColorChanged)}

是否可以在MyQuickItem中监控OnNextColorChanged?

解决方案

我们可以使用 QMetaObject 来获取属性和信号，然后我们通过旧式连接:

#ifndef MYQUICKITEM_H#define MYQUICKITEM_H#include #include 类 MyQuickItem : 公共 QQuickItem{Q_OBJECT上市:MyQuickItem(QQuickItem *parent = Q_NULLPTR): QQuickItem(parent){}受保护:void componentComplete(){int index =metaObject()->indexOfProperty("nextColor");const QMetaProperty property = metaObject()->property(index);如果(property.hasNotifySignal()){const QMetaMethod s = property.notifySignal();QString sig = QString("2%1").arg(QString(s.methodSignature()));连接(这个，sig.toStdString().c_str()，这个，SLOT(onNextColorChanged()))；}}私人插槽:void onNextColorChanged(){int index =metaObject()->indexOfProperty("nextColor");const QMetaProperty property = metaObject()->property(index);qDebug()<<颜色"<<property.read(this);}};#endif//MYQUICKITEM_H

完整示例可在以下链接中找到.>

I am using Qt 5.9.3. I have following property declared in my app's main.qml

Code:

//main.qml
MyQuickItem {

    property color nextColor
    onNextColorChanged: {
        console.log("The next color will be: " + nextColor.toString())
    }
}

// MyQuickItem.h
class MyQuickItem : public QQuickItem {

}

Question:

How can I make onNextColorChanged be defined in the C++ side?

I know that I can also make nextColor as a property inside C++ class MyQuickItem. like so

// MyQuickItem.h
class MyQuickItem : public QQuickItem {

    Q_PROPERTY(QColor nextColor READ nextColor WRITE setNextColor NOTIFY nextColorChanged)
}

Is it possible to monitor OnNextColorChanged inside MyQuickItem?

解决方案

We can use the QMetaObject to obtain the property and the signal, then we connect it through the old style:

#ifndef MYQUICKITEM_H
#define MYQUICKITEM_H

#include <QQuickItem>
#include <QDebug>

class MyQuickItem : public QQuickItem
{
    Q_OBJECT
public:
    MyQuickItem(QQuickItem *parent = Q_NULLPTR): QQuickItem(parent){}
protected:
    void componentComplete(){
        int index =metaObject()->indexOfProperty("nextColor");
        const QMetaProperty property = metaObject()->property(index);
        if (property.hasNotifySignal()){
            const QMetaMethod s = property.notifySignal();
            QString sig = QString("2%1").arg(QString(s.methodSignature()));
            connect(this, sig.toStdString().c_str() , this, SLOT(onNextColorChanged()));
        }
    }
private slots:
    void onNextColorChanged(){
        int index =metaObject()->indexOfProperty("nextColor");
        const QMetaProperty property = metaObject()->property(index);
        qDebug()<<"color" << property.read(this);
    }
};

#endif // MYQUICKITEM_H

The complete example can be found in the following link.

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