从元对象获取属性更改通知程序

Obtain property changed notifier from meta-object

本文关键字：通知 程序 属性 对象 获取      更新时间：2023-10-16

我想编写一个属性连接器，用于以QML方式连接C++Qt中的属性。可能是这样的：

new PropConnector ( receiver, "propName", sender, "propName" );

propConnector 类是一个小型 QObject 类，它使用发送方作为父级，侦听属性更改的信号并设置接收方的适当属性。喜欢这个：

class PropConnector : public QObject
{
    Q_OBJECT
private:
    QObject *_sender;
    QObject *_receiver;
    QString _senderProp;
    QString _receiverProp;
public:
    PropConnector(QObject *sender, QObject *receiver, QString senderProp, QString receiverProp) : 
      QObject(sender)
      ,_sender(sender)
      ,_receiver(receiver)
      ,_senderProp(senderProp)
      ,_receiverProp(receiverProp)
    { 
        // Is it possible to get the proper property-changed notifier signal?
        //connect(sender, SIGNAL( on<PROPERTY>Changed() ), this, SLOT( forward ) );
    }
private slots:
    void forward()
    {
        _receiver->setProperty( receiverProp, _sender->property( senderProp ) );
    }
};

唯一的问题是，如何找到我要收听的属性名称的正确信号名称？我想，这是可能的，但直到现在我才通过阅读元对象文档来发现。

编辑：在凯文的建议下，我能够实现该类。

propconnector.h

#ifndef PROPCONNECTOR_H
#define PROPCONNECTOR_H
#include <QObject>
#include <QString>
class PropConnector : public QObject
{
    Q_OBJECT
private:
    QObject *_sender;
    QObject *_receiver;
    QString _senderProperty;
    QString _receiverProperty;
public:
    PropConnector(QObject *sender, QString senderProperty, QObject *receiver, QString receiverProperty);
private slots:
    void forward();
};
#endif // PROPCONNECTOR_H

支柱连接器.cpp

#include "propconnector.h"
#include <QMetaObject>
#include <QMetaProperty>
PropConnector::PropConnector(QObject *sender, QString senderProperty, QObject *receiver, QString receiverProperty) : 
  QObject(sender)
  ,_sender(sender)
  ,_receiver(receiver)
  ,_senderProperty(senderProperty)
  ,_receiverProperty(receiverProperty)
{ 
    const QMetaObject *senderMeta = sender->metaObject();
    const int index = senderMeta->indexOfProperty(senderProperty.toUtf8().constData());
    if (index != -1) {
        const QMetaProperty p = senderMeta->property(index);
        if ( p.hasNotifySignal() ) {
            const QMetaMethod s = p.notifySignal();
            QString sig = QString("2%1").arg(s.signature());
            const char *ssig = SLOT(forward());
            bool ok = connect(sender, sig.toStdString().c_str() , this, SLOT(forward()));   
            int i=0;
            i++;
        }
    }       
}
void PropConnector::forward()
{
    _receiver->setProperty( _receiverProperty.toStdString().c_str(), _sender->property( _senderProperty.toStdString().c_str() ) );
}

您可以从QMetaProperty获取该信息 

QMetaObject *senderMeta = sender->metaObject();
const int index = senderMeta->indexOfProperty(senderProperty.toUtf8().constData());
if (index != -1) {
    const QMetaProperty property = senderMeta->property(index);
    if (property.hasNotifySignal) {
        const QMetaMethod notifySignal = property.notifySignal();
        connect(sender, notifySignal, receiver, metaMethodOfSlot);     
    }
}

未经测试，可能无法编译。 metaMethodOfSlot是接收器插槽的QMetaMethod，请以类似的方式获取。

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