Qt QML signal and slot connection

[Jerwinprabu]

Hi,

I am a Roboticist, I am using Qt c++ (Embedded) for my project work. Already I have developed code for my Robot in normal UI. Using that UI I have connected signals and slots.

Now I would like to create a UI like car, bike dashboard, I have decided to create a new dashboard UI, I have created dashboard also (Dashboard gauge style (circular), button (stop, start, forward, Reverse, Mode 1 and Mode 2 button, Emergency button) ).

I need to connect signal and slot, everything with existing code, is it possible ? that existing normal UI having same button, I am not familiar in Qt QML, so for further step I need guidance !!!

[dheerendra]

welcome to the forum. Question is not very clear on what you would like to achieve ? Are you telling that you have written the UI in QML and would like to have signal/slot communication from Qt ? Is that the question ? If yes, it is possible. If this is not your question please give more details.

[raven-worx]

@Jerwinprabu said:

I need to connect signal and slot, everything with existing code, is it possible ? that existing normal UI having same button, I am not familiar in QT QML, so for further step I need guidance !!!

This should get you covered with everything you need.

[Jerwinprabu]

Ya, exactly. Thanks for your support. I need to connect signal and slot, everything with existing code, is it possible ? that existing normal UI having same button, I am not familiar in QT QML, so for further step I need guidance !!!

[raven-worx]

@Jerwinprabu
You should start reading about QML to get an overview.
Basically you can create a QObject subclass which just forwards calls from QML to your existing C++ code and vice versa.

[Jerwinprabu]

For example, Dialog.h

#ifndef DIALOG_H
#define DIALOG_H
#include <QDialog>

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();

    bool startThreadflag;
    bool stopThreadflag;

private:
    Ui::Dialog *ui;

public slots:

    void startThread();
    void stopThread();

private slots:

    void on_Start_2_clicked();
    void on_Stop_2_clicked();
    void on_Close_clicked();
    void on_Left_clicked();
    void on_Right_clicked();
};

#endif // DIALOG_H

Dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
#include <QDebug>
#include <iostream>     
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdint.h>

using namespace std;

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);

    startThreadflag = false;
    stopThreadflag = true;
}

Dialog::~Dialog()
{
    delete ui;
}

void  Dialog:: startThread(){

    if(!startThreadflag){

    this->ui->Start_2->setEnabled(false);
    this->ui-> Stop_2->setEnabled(true);

    startThreadflag = true;
    stopThreadflag = false;

    }
}

void Dialog::on_Start_2_clicked()
{
    startThread();
}

void Dialog:: stopThread(){

    if(!stopThreadflag){
            cout << "Closing threads"<< endl;

        this->ui->Start_2->setEnabled(true);
        this->ui->Stop_2->setEnabled(false);

        stopThreadflag= true;
        startThreadflag = false;
    }
}

void Dialog::on_Stop_2_clicked()
{
    stopThread();
}

void Dialog::on_Close_clicked()
{
    cout<<"close_clicked"<<endl;

    this->close();
}

void Dialog::on_Left_clicked()
{
    cout<<"Left Clicked"<<endl;
}
void Dialog::on_Right_clicked()
{
    cout<<"Right Clicked"<<endl;
}

main.cpp

#include "dialog.h"
#include <QApplication>
using namespace std;

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Dialog w;
    w.show();

    return a.exec();
}

That existing normal UI and qml having same button. I need to connect signal and slot in qt qml.

[medyakovvit]

@Jerwinprabu it's not Qt Quick/Qml application it's Qt Widgets app. Do you want to rewrite your gui from Qt Widgets to Qt Quick/Qml?

[Jerwinprabu]

@medyakovvit ya exactly. First I have developed my code in Qt Widgets. For dashboard design I want to rewrite gui from Qt Widgets to Qt Quick/Qml. I have designed button and everything (Except signals and slot) . For example

Button {
       id:sender
        x:220
        y:295
        text: "Start"
        signal buttonClicked(string text)
        onClicked: {
           sender.buttonClicked.connect(receiver.changeText);
           sender.buttonClicked(" Started !!!")
                   }
          style: ButtonStyle {
           background: Rectangle {
                       implicitWidth: 100
                       implicitHeight: 40
                       border.width: control.activeFocus ? 1 : 2
                       border.color: "green"
                       radius: 10
gradient: Gradient {
   GradientStop { position: 5 ; color: control.pressed ? "green" : "#eee" }
   GradientStop { position: 6 ; color: control.pressed ? "green" : "#ccc" }

         }
       }
    }
 }

Button {
      id: receiver
       x:240
       y:-260
       text: "Welcome !!! Waiting for your Response !!!"
       function changeText(text) {
      receiver.text = text;
             }
       style: ButtonStyle {
            background: Rectangle {
             implicitWidth: 550
             implicitHeight: 50
             border.width: control.activeFocus ? 1 : 2
             border.color: "black"
             radius: 10
gradient: Gradient {
  GradientStop { position: 5 ; color: control.pressed ? "#eee" : "white" }
   GradientStop { position: 6 ; color: control.pressed ? "#ccc" : "white" }

         }
       }
     }
  }

[Bharathi]

You are trying to pass the String as argument from qml after clicking(signal) the button and pass it to qtwidgets(slots)???

[srikanth06]

Hpow did you solve this?

[Pablo J. Rogina]

@srikanth06 have you checked the documentation for QML + C++ integration?

[srikanth2006]

yes i did but I cant seem to get the solutions