从元对象获取属性更改通知

Posted 2023-02-16

【中文标题】从元对象获取属性更改通知

【英文标题】：Obtain property changed notifier from meta-object

【发布时间】：2017-01-08 11:04:03

【问题描述】：

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。像这样：

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，我怎样才能找到我想听的属性名称的正确信号名称？我想，这是可能的，但我直到现在通过阅读元对象文档才知道。

编辑：在 Kevin 的建议下，我得以实现该类。

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

propconnector.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() ) );

【参考方案1】：

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 将是接收器插槽的QMetaMethod，以类似的方式获得。

【讨论】：

酷，有帮助。接收器信号并不重要，因为连接只是单向的。信号是从连接器类本身发出的。我已经在问题编辑中发布了代码。