c++ and qml binding

**ganeshgladish** · 6th May 2013, 12:42

hi,
how to receive signal from c++ to qml....using qdeclarativeview i am able to bind qml with c++ but i don't know how to bind c++ with qml....

**wysota** · 6th May 2013, 13:52

Expose a C++ object to QML engine using QDeclarativeContext::setContextProperty() and use one of the means available (either the Connections element or javascript object.signal.connect(slot) expression) to connect a QML function to such object's signal.

**ganeshgladish** · 6th May 2013, 15:01

thank you for your reply,
here i am using qml for ui and c++ for database ....whenever i retrieve data from c++.... i want to give to qml..

**anda_skoa** · 6th May 2013, 15:24

You might want to consider exposing the data as a model.
Maybe you can even use QSqlQueryModel?

Cheers,
_

**ganeshgladish** · 7th May 2013, 12:54

thank you for your reply,
but error is comming like this,
QMetaObject::invokeMethod: No such method QDeclarativeRectangle::myQmlFunction(QVariant)
QML function returned: ""

thank you for your reply,
but error is comming like this,
QMetaObject::invokeMethod: No such method QDeclarativeRectangle::myQmlFunction(QVariant)
QML function returned: ""

**wysota** · 7th May 2013, 13:42

Show your code please.

**ganeshgladish** · 7th May 2013, 14:48

this is my qt-c++ code, here i am checking user name and password,if user name and password matching true means i am send string "hai" to my qml...in qml i am checking that string then i taking decision.....
that userin and passin coming from qml using qdeclarative......

Qt Code:

Switch view

Q_INVOKABLE void login_database(const QString &userin,const QString &passin)
{
    QSqlQuery querylogin(db);
    if(db.isOpen())
    {
     querylogin.exec("SELECT * FROM hospital WHERE UserName=\'"+userin+"\'");
     if(!querylogin.exec())
     {
        QMessageBox::information(this, tr("Login Match"),tr("Sorry query is not execute"),QMessageBox::Ok);
     }
 
        else
     {
         QString Pass,Uname;
                     bool matchPass=FALSE;
                     bool matchUname=FALSE;
                     while (querylogin.next())
                     {
                         Uname=querylogin.value(1).toString();
                         Pass = querylogin.value(2).toString();
 
                         if(Uname==userin)
                             matchUname=TRUE;
 
 
                         }
 
 
 
 
                             if(!matchUname)
                             {
 
                                 QMessageBox::information(this, tr("Login Match"),tr("Invalid Username"),QMessageBox::Ok);
 
                             }
 
                             else if(!matchPass)
                             {
                              //   loginlbl->setText("Wrong Password");
                                 QMessageBox::information(this, tr("Login Match"),tr("Invalid Password"),QMessageBox::Ok);
                                 return;
                             }
 
                             else
                             {
 
                                QMessageBox::information(this, tr("Login Match"),tr("Sucessfully ur login to database"),QMessageBox::Ok);
 
 
                              QDeclarativeEngine engine1;
                               QDeclarativeComponent component(&engine1, "main.qml");
                                QObject *object = component.create();
 
                                QVariant returnedValue;
                                QVariant msg = "Hello from C++";
                                QMetaObject::invokeMethod(object, "myQmlFunction",
                                        Q_RETURN_ARG(QVariant, returnedValue),
                                        Q_ARG(QVariant, msg));
 
                                qDebug() << "QML function returned:" << returnedValue.toString();
                                delete object;
 
 
 
     }
 
 
     }
 
 
 
 
}

Q_INVOKABLE void login_database(const QString &userin,const QString &passin)
{
    QSqlQuery querylogin(db);
    if(db.isOpen())
    {
     querylogin.exec("SELECT * FROM hospital WHERE UserName=\'"+userin+"\'");
     if(!querylogin.exec())
     {
        QMessageBox::information(this, tr("Login Match"),tr("Sorry query is not execute"),QMessageBox::Ok);
     }

        else
     {
         QString Pass,Uname;
                     bool matchPass=FALSE;
                     bool matchUname=FALSE;
                     while (querylogin.next())
                     {
                         Uname=querylogin.value(1).toString();
                         Pass = querylogin.value(2).toString();

                         if(Uname==userin)
                             matchUname=TRUE;


                         }




                             if(!matchUname)
                             {

                                 QMessageBox::information(this, tr("Login Match"),tr("Invalid Username"),QMessageBox::Ok);

                             }

                             else if(!matchPass)
                             {
                              //   loginlbl->setText("Wrong Password");
                                 QMessageBox::information(this, tr("Login Match"),tr("Invalid Password"),QMessageBox::Ok);
                                 return;
                             }

                             else
                             {

                                QMessageBox::information(this, tr("Login Match"),tr("Sucessfully ur login to database"),QMessageBox::Ok);


                              QDeclarativeEngine engine1;
                               QDeclarativeComponent component(&engine1, "main.qml");
                                QObject *object = component.create();

                                QVariant returnedValue;
                                QVariant msg = "Hello from C++";
                                QMetaObject::invokeMethod(object, "myQmlFunction",
                                        Q_RETURN_ARG(QVariant, returnedValue),
                                        Q_ARG(QVariant, msg));

                                qDebug() << "QML function returned:" << returnedValue.toString();
                                delete object;



     }


     }




}

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Added after 7 minutes:

here i am using qml for gui...here i am enter username and password,then i am click login button then that text goto c++ da

javascript Code:

Switch view

// import QtQuick 1.0 // to target S60 5th Edition or Maemo 5
import QtQuick 1.1
 
    Rectangle {
        id:hdcs_ui_login_rect1
        width: 1600
      height:900
   //   color:"red"
 
 
      Image {
          id: back
 
          anchors.fill: parent
          source: "img/backg.png"
          cache: true
 
      }
 
 
      Rectangle{
 
 
          id:outline
          width: parent.width/1.2
          height: parent.height/1.2
          color: "transparent"
          anchors.centerIn: parent
 
 
 
          Image {
              id:login
 
              anchors.topMargin: 11
              source: "img/doctors_26.png"
              cache: true
 
 
          }
 
          Rectangle{
 
 
              id:outline1
              width: parent.width/2
              height: parent.height/1.8
              color: "transparent"
              anchors.centerIn: parent
 
 
              Image {
                  id:login1
 
                  anchors.topMargin: 11
                  anchors.fill:     parent
 
 
                //  anchors.top:coll.top
                  source: "img/newimage1.png"
                  cache: true
 
 
              }
 
 
      Column
      {
          id:coll
          anchors.centerIn: parent
          spacing: 30
 
 
 
          Column{
              spacing: 5
              Text {
                  id: title
                  text: qsTr("Login")
                  font.pixelSize: 30
                  color:"white"
                  font.bold: true
              }
 
          }
 
 
 
 
          Column{
              spacing: 5
              Text {
                  id: name
                  text: qsTr("User Id:")
                  font.pixelSize: 20
                  color:"white"
              }
              Rectangle{
                  id:rect
                  width: 300
                  height: 30
                   color:    "white"
 
              TextInput
              {
                  id: userInputlog
                  width: parent.width-6
                  height: parent.height-6
                  anchors.centerIn: parent
                  font.pixelSize: 15
                  font.bold: true
                  maximumLength: 15
 
              }
          }
          }
          Column
          {
              spacing: 5
              Text {
                  id: passlog
                  text: qsTr("Password:")
                  font.pixelSize: 20
              //    font.bold: true
                  color:"white"
              }
              Rectangle{
                  id:rect1
                  width: 300
                  height: 30
                   color:    "white"
 
              TextInput
              {
                  id: passwordInput
                  width: parent.width-6
                  height: parent.height-6
                  anchors.centerIn: parent
                  font.pixelSize: 15
                  font.bold: true
                  maximumLength: 15
                  echoMode: TextInput.Password
 
              }
              }
          }
 
          Rectangle{
            //  spacing: 100
              id:buttons
              width: parent.width
              color: "transparent"
 
 
          }
 
         Row{
             spacing: 20
             anchors.horizontalCenter: parent.horizontalCenter
 
 
             Image {
                 id: img
                 source: "img/re1.png"
                  fillMode: Image.PreserveAspectFit
                 Text {
                     id:log
                     text: qsTr("Login")
                     anchors.centerIn: parent
                     color:"white"
                     font.pixelSize: 20
                     font.bold:true
 
                 }
 
 
                 function myQmlFunction(msg) {
                     console.log("Got message:", msg)
                     return "some return value"
                 }
 
                 MouseArea
                 {
                     anchors.fill: parent
                     onPressed:
                     {
                         myObject.login_database(userInputlog.text,passlog.text);
 
                         function myQmlFunction(msg) {
                                console.log("Got message:", msg);
 
                             if(msg == userInputlog.text)
                         {
                             loader.source = "HDCS_UI_DR_CHF.qml"
 
                         }
 
 
                         }
 
 
 
 
                     }
 
 
                 }
 
             }
 
 
             Image {
                 id: img1
                 source: "img/re1.png"
                 Text {
                     id:log2
                     anchors.leftMargin: 20
                     text: qsTr("Forgot Password")
                     anchors.centerIn: parent
                     color:"white"
                     font.bold: true
                     font.pixelSize: 20
                 }
             }
 
         }
      }
          }
 
 
 
      }
 
      Image {
          id: shutdown
          anchors.verticalCenterOffset: 350
          anchors.horizontalCenterOffset: 550
          anchors.horizontalCenter:parent.horizontalCenter
          anchors.verticalCenter: parent.verticalCenter
 
          source: "img/power.png"
          cache: true
          smooth: true
 
          MouseArea{
 
              anchors.fill: parent
              onClicked:
              {
 
                  Qt.quit();
              }
 
          }
 
      }
 
 
      Loader {
             id: loader
 
 
             anchors.fill: parent
             focus: true
         }
 
 
    }

// import QtQuick 1.0 // to target S60 5th Edition or Maemo 5
import QtQuick 1.1

    Rectangle {
        id:hdcs_ui_login_rect1
        width: 1600
      height:900
   //   color:"red"


      Image {
          id: back

          anchors.fill: parent
          source: "img/backg.png"
          cache: true

      }


      Rectangle{


          id:outline
          width: parent.width/1.2
          height: parent.height/1.2
          color: "transparent"
          anchors.centerIn: parent



          Image {
              id:login

              anchors.topMargin: 11
              source: "img/doctors_26.png"
              cache: true


          }

          Rectangle{


              id:outline1
              width: parent.width/2
              height: parent.height/1.8
              color: "transparent"
              anchors.centerIn: parent


              Image {
                  id:login1

                  anchors.topMargin: 11
                  anchors.fill:     parent


                //  anchors.top:coll.top
                  source: "img/newimage1.png"
                  cache: true


              }


      Column
      {
          id:coll
          anchors.centerIn: parent
          spacing: 30



          Column{
              spacing: 5
              Text {
                  id: title
                  text: qsTr("Login")
                  font.pixelSize: 30
                  color:"white"
                  font.bold: true
              }

          }




          Column{
              spacing: 5
              Text {
                  id: name
                  text: qsTr("User Id:")
                  font.pixelSize: 20
                  color:"white"
              }
              Rectangle{
                  id:rect
                  width: 300
                  height: 30
                   color:    "white"

              TextInput
              {
                  id: userInputlog
                  width: parent.width-6
                  height: parent.height-6
                  anchors.centerIn: parent
                  font.pixelSize: 15
                  font.bold: true
                  maximumLength: 15

              }
          }
          }
          Column
          {
              spacing: 5
              Text {
                  id: passlog
                  text: qsTr("Password:")
                  font.pixelSize: 20
              //    font.bold: true
                  color:"white"
              }
              Rectangle{
                  id:rect1
                  width: 300
                  height: 30
                   color:    "white"

              TextInput
              {
                  id: passwordInput
                  width: parent.width-6
                  height: parent.height-6
                  anchors.centerIn: parent
                  font.pixelSize: 15
                  font.bold: true
                  maximumLength: 15
                  echoMode: TextInput.Password

              }
              }
          }

          Rectangle{
            //  spacing: 100
              id:buttons
              width: parent.width
              color: "transparent"


          }

         Row{
             spacing: 20
             anchors.horizontalCenter: parent.horizontalCenter


             Image {
                 id: img
                 source: "img/re1.png"
                  fillMode: Image.PreserveAspectFit
                 Text {
                     id:log
                     text: qsTr("Login")
                     anchors.centerIn: parent
                     color:"white"
                     font.pixelSize: 20
                     font.bold:true

                 }


                 function myQmlFunction(msg) {
                     console.log("Got message:", msg)
                     return "some return value"
                 }

                 MouseArea
                 {
                     anchors.fill: parent
                     onPressed:
                     {
                         myObject.login_database(userInputlog.text,passlog.text);
                
                         function myQmlFunction(msg) {
                                console.log("Got message:", msg);
  
                             if(msg == userInputlog.text)
                         {
                             loader.source = "HDCS_UI_DR_CHF.qml"

                         }


                         }




                     }


                 }

             }


             Image {
                 id: img1
                 source: "img/re1.png"
                 Text {
                     id:log2
                     anchors.leftMargin: 20
                     text: qsTr("Forgot Password")
                     anchors.centerIn: parent
                     color:"white"
                     font.bold: true
                     font.pixelSize: 20
                 }
             }

         }
      }
          }



      }

      Image {
          id: shutdown
          anchors.verticalCenterOffset: 350
          anchors.horizontalCenterOffset: 550
          anchors.horizontalCenter:parent.horizontalCenter
          anchors.verticalCenter: parent.verticalCenter

          source: "img/power.png"
          cache: true
          smooth: true

          MouseArea{

              anchors.fill: parent
              onClicked:
              {

                  Qt.quit();
              }

          }

      }


      Loader {
             id: loader


             anchors.fill: parent
             focus: true
         }


    }

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**wysota** · 7th May 2013, 20:10

Your code is bizzare... you're creating a QML UI as a response to SQL query? I have no idea what you are trying to acomplish but it looks like you should study the difference between declarative and imperative programming. Not speaking of trying to call some function on some object that is defined in a totally different object. No wonder it doesn't work, right?

**anda_skoa** · 8th May 2013, 14:19

If all you need is to communicate a successful login to the QtQuick UI, it would be a lot easier to have a property for that on your C++ object and to change it when login succeeds.

The QML code can then just bind to that property.

Something like

Qt Code:

Switch view

loader.source = myobject.loggedIn ? "HDCS_UI_DR_CHF.qml" : ""

loader.source = myobject.loggedIn ? "HDCS_UI_DR_CHF.qml" : ""

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Cheers,
_

Thread: c++ and qml binding

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