QML c++ TCP Socket to instance connection in all classes

[Nio74]

Good Night

I have to initialize the opening of the server in the main.qml but that it is not work to all the classes, I tried to use on my main.qml:

Component.onCompleted: {

//method why connect to tcpSocket
        backend.connectClicked()
    }

this is my instantiation c++ to qml

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "backend.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);
    
    //Pass my c++ to Qml
    qmlRegisterType<Backend>("io.qt.Backend", 1, 0, "Backend");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

this i my complete main.qml:

import QtQuick 2.2
import QtQuick.Controls 1.2
import io.qt.Backend 1.0

ApplicationWindow {
    width: 600
    height: 481
    visible: true

   Backend{
       id: backend
   }

    Rectangle {
        color: "#212126"
        anchors.fill: parent
    }

    toolBar: BorderImage {
        border.bottom: 8
        source: "images/toolbar.png"
        width: parent.width
        height: 70

        Rectangle {
            id: backButton
            width: opacity ? 60 : 0
            anchors.left: parent.left
            anchors.leftMargin: 20
            opacity: stackView.depth > 1 ? 1 : 0
            anchors.verticalCenter: parent.verticalCenter
            antialiasing: true
            height: 60
            radius: 4
            color: backmouse.pressed ? "#222" : "transparent"
            Behavior on opacity { NumberAnimation{} }
            Image {
                anchors.verticalCenter: parent.verticalCenter
                source: "images/navigation_previous_item.png"
            }
            MouseArea {
                id: backmouse
                anchors.fill: parent
                anchors.margins: -10
                onClicked: stackView.pop()
            }
        }

        Text {
            font.pixelSize: 42
            Behavior on x { NumberAnimation{ easing.type: Easing.OutCubic} }
            x: backButton.x + backButton.width + 20
            anchors.verticalCenter: parent.verticalCenter
            color: "white"
            text: "Client Paolo"
        }
    }

    ListModel {
        id: pageModel
        ListElement {
            title: "Riparazioni"
            page: "Riparazioni.qml"
        }
        ListElement {
            title: "Magazzino"
            page: "Magazzino.qml"
        }
        /*
        ListElement {
            title: "ProgressBar"
            page: "content/ProgressBarPage.qml"
        }
        ListElement {
            title: "Tabs"
            page: "content/TabBarPage.qml"
        }
        ListElement {
            title: "TextInput"
            page: "content/TextInputPage.qml"
        }
        ListElement {
            title: "List"
            page: "content/ListPage.qml"
        }  */
    }

    StackView {
        id: stackView
        anchors.fill: parent
        // Implements back key navigation
        focus: true
        Keys.onReleased: if (event.key === Qt.Key_Back && stackView.depth > 1) {
                             stackView.pop();
                             event.accepted = true;
                         }

        initialItem: Item {
            width: parent.width
            height: parent.height
            ListView {
                model: pageModel
                anchors.fill: parent
                delegate: AndroidDelegate {
                    text: title
                    onClicked: stackView.push(Qt.resolvedUrl(page))
                }
            }
        }
    }

    Component.onCompleted: {
        backend.connectClicked()
    }

}

this is other class where I use method for pass data at server

import QtQuick 2.12
import QtQuick.Controls 2.5
import io.qt.Backend 1.0

Item
{
    id: element

    Backend {
        id: backend
    }

    Row {
        id: row1
        height: 50
        anchors.right: parent.right
        anchors.rightMargin: 5
        anchors.left: parent.left
        anchors.leftMargin: 5
        anchors.top: parent.top
        anchors.topMargin: 3

        Rectangle {
            id: rectangle_Search
            height: 44
            color: "#0e99b2"
            anchors.top: parent.verticalCenter
            anchors.topMargin: -25
            anchors.left: parent.left

            anchors.right: parent.right


            Text {
                id:lbl_SearchCode
                color: "#0a0808"
                text: qsTr("Codice")
                anchors.verticalCenter: parent.verticalCenter
                anchors.left: parent.left
                anchors.leftMargin: 4
                font.pixelSize: 12
            }

            CustomTextEdit {
                id: c_Txt_codice
                y: 0
                width: 50
                height: 20
                anchors.verticalCenter: parent.verticalCenter
                anchors.bottom: parent
                anchors.bottomMargin: 0
                anchors.left: lbl_SearchCode.right
                anchors.leftMargin: 20

            }

            CustomButton {
                id: btnSearchKey
                x: 583
                y: 3
                text: "S"
                anchors.verticalCenter: parent.verticalCenter
                anchors.right: parent.right
                anchors.rightMargin: 5
                anchors.top: parent.verticalCenter
                anchors.topMargin: -22
                color: enabled ? this.down ? "#78C37F" : "#87DB8D" : "gray"
                onClicked: {
                    backend.connectClicked()
                    backend.sendClicked(c_Txt_codice.text)
                }
            }

        }
    }
    Row {
        id: row2
        height: 200
        anchors.right: parent.right
        anchors.rightMargin: 3
        anchors.left: parent.left
        anchors.leftMargin: 3
        anchors.top: row1.bottom
        anchors.topMargin: 2

        Rectangle{
            id: rectangle_Articolo
            color: "#0e99b2"
            anchors.fill: parent



            Label{
                id: lbl_NBusta
                color: "#ebedef"
                text: "N°Busta"
                anchors.left: parent.left
                anchors.leftMargin: 5
                anchors.top: parent.top
                anchors.topMargin: 10
            }

            Text {
                id: txt_NBusta
                width: 40
                height: 15
                text: qsTr("Text")
                anchors.top: parent.top
                anchors.topMargin: 10
                anchors.left: lbl_NBusta.right
                anchors.leftMargin: 5
                font.pixelSize: 12
            }

        }

    }
}

but if not use " backend.connectClicked()" not work

error:

QIODevice::write (QTcpSocket): device not open

[SGaist]

Hi,

Based on the method name, why should the backend connect to the GUI ?

Also, since part of the error message comes from that Backend class, you should share its implementation.

[Nio74]

@SGaist said in QML c++ TCP Socket to istance connection in all classes:

Hi,
Based on the method name, why should the backend connect to the GUI ?
Also, since part of the error message comes from that Backend class, you should share its implementation.

the backend is done in c ++ where I'm developing the reception and the data transfer QTCPSoket.Però if I instantiate the connection to the server on each class works correctly, but I would like that when the app starts the client connects only once and then be used on all the qml classes always if it will be possible.

[SGaist]

That I understood.

If you want only one instance of your backed to be used, you can also simply make it a context property of your engine root context.

That will likely simplify things.

[Nio74]

@SGaist said in QML c++ TCP Socket to instance connection in all classes:

That I understood.

If you want only one instance of your backed to be used, you can also simply make it a context property of your engine root context.

That will likely simplify things.

Tanks I did as you said:

 Backend backend;

    QQmlContext *context = engine.rootContext();
    context->setContextProperty("backend",&backend);```