CODEWITHSUNDEEP
c++qt
Keshav Sharma
Keshav Sharma

Reputation: 124

Creating custom property in Qt with c++

I am new to Qt and trying to create a custom property in Qt. For keeping it short i have merged the .h and .cpp file here but they are different in my main project. My main.cpp is

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "message.h"
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;
    Message msg;
    engine.rootContext()->setContextProperty("msg", &msg);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    qRegisterMetaType<MessageBody*>("MessageBody*");
    return app.exec();
}

My message.h is

#include<messageBody.h>
class Message : public QObject
{
    Q_OBJECT
    Q_PROPERTY(MessageBody* body READ body WRITE setBody NOTIFY bodyChanged)
    MessageBody ob;
public:
    MessageBody* body()
    {
        return &ob;
    }
    void setBody(MessageBody* body)
    {
         ob.textUpdate(body->text());
         emit bodyChanged();
    }

signals:
    void bodyChanged();
};

My messageBody.h is

class MessageBody : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString text READ text WRITE textUpdate NOTIFY textChanged)
    QString ori_text;
public:
    void textUpdate(const QString& new_txt)
    {
        if(new_txt != ori_text)
        {
            ori_text=new_txt;
            emit textChanged();
        }
    }
    QString text()
    {
        return ori_text;
    }

    signals:
        void textChanged();
};

My main.qml is

import QtQuick 2.3
import QtQuick.Controls 1.2

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    Text{
        msg.body: "Hello, world!" //"Error here."
                             //I am expecting MessageBody::textUpdate()
                             //to get called i.e write method of Property
    }
}

While executing, I am getting an error

 qrc:/main.qml:18 Cannot assign to non-existent property "msg"

Thanks for the help.

Upvotes: 2

Views: 883

Answers (2)

avb
avb

Reputation: 1751

I don't get 100% what you're tring to achieve, but maybe something like this:

main.qml

import QtQuick 2.3
import QtQuick.Controls 1.2

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    Text{
        text: msg.body.text
    }

    Component.onCompleted: {
        msg.body.text = "Hello, world!"
    }
}

main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "message.h"
#include "MessageBody.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;

    qRegisterMetaType<MessageBody*>("MessageBody");
    qRegisterMetaType<Message *>("Message");

    Message msg;
    engine.rootContext()->setContextProperty("msg", &msg);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

Does this work?

Upvotes: 2

David Gonzalez
David Gonzalez

Reputation: 655

This is because you are using your msg object as if it was an existing property of the QML Text Element and it is not that's why Qt give you this error.

I am not a QML pro developer but as I know you could or call your msg.body with an existing signal of the Text Object such as onTextChange o Component.onCompleted or try to create a custom QML object inheriting from Text and that has a custom property msg.body which make a link with your msg.body of your c++ object.

Upvotes: 2

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