Strange behaviour when open QML Popup Window from C++ code.

[Dong]

Hi everyone !
I'm implement M-V-VM Pattern and have this Strange Behaviour

First, I open a main window like normal. then set the Context Object like this:

//Set Data Context to the Root Context
QObject* mainViewModel = new MainWindowViewModel(window);
QQmlContext* ctx = engine.rootContext();
ctx->setContextObject(mainViewModel);

Then I'm try to open Popup in MainWindowViewModel like this:

QQmlApplicationEngine engine;

QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/FrmAuthenticate.qml")));
QObject *childItem = qobject_cast<QObject*>(component.create());
QQuickWindow *dialog = qobject_cast<QQuickWindow *>(childItem);
QQmlContext* ctx = engine.contextForObject(dialog);
FrmAuthenticateViewModel *viewModel = new FrmAuthenticateViewModel(dialog);
ctx->setContextObject(viewModel);
childItem->setParent(this->parent());

in Popup I have a WebView and it print out - console.log() - each time it navigate to new Url.

First strange thing:

• If open the popup by create a component from QML, I got the log data.
  But when open from ViewModel, No log data print to Application Output (Can't debug in QML too)

Second strange thing:

• In the code to open popup above, I cannot set the contextObject for the Popup.
  It show a warning "Cannot set context object for internal context" at runtime and QML cannot call to ViewModel's functions

Third strange thing:

• If open the popup by code in ViewModel without set the contextObject. Webview load & display the default page.
  When trying to set contextObject. Webview cannot load & display the default page.

Anyone have any ideal why this happen ?!

Thanks & Best Regards
DongLD

[Dong]

Please... anyone can help me with this ?!

Just open a popup from C++ & setContextObject for it.

[Dong]

I'm try to build simple sample. Don't know why, but it work (mostly)

• I can set context object to component
• I can get a property from context by calling View Model's binding function

• But I can't "connect" the signal from Qml to C++ functions like main.qml call to showLoginDialog() function
  • It look like all signals in Qml wasn't fired. (No focus highlight, button onClicked not fired...

Here is the code:

main.qml

import QtQuick 2.3
import QtQuick.Controls 1.2

ApplicationWindow {
    id : mainWindow
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    menuBar: MenuBar {
        Menu {
            title: qsTr("File")
            MenuItem {
                text: qsTr("&Open")
                onTriggered:
                {
                    //Show popup from ViewModel (C++)
                    showLoginDialog();

                    //Show popup from QML
//                    var component = Qt.createComponent("qrc:/login.qml");
//                    if (component.status == Component.Ready)
//                    {
//                        component.createObject(mainWindow);
//                    }
                }
            }
            MenuItem {
                text: qsTr("Exit")
                onTriggered: Qt.quit();
            }
        }
    }
}

main.cpp

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

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    QObject *topLevel = engine.rootObjects().at(0);
    QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);

    //Set Data Context to the Root Context
    QObject* mainViewModel = new MainWindowViewModel(window);
    QQmlContext* ctx = engine.rootContext();
    ctx->setContextObject(mainViewModel);
}

mainwindowviewmodel.cpp

#include "mainwindowviewmodel.h"

MainWindowViewModel::MainWindowViewModel(QObject *parent) : QObject(parent)
{

}

void MainWindowViewModel::showLoginDialog()
{
    qDebug() << "Show Login Form";

    LoginViewModel *viewModel = new LoginViewModel();
    viewModel->setProperty("sampleText", "https://google.com");
    QQmlApplicationEngine engine;

    QQmlContext* ctx = new QQmlContext(engine.rootContext());
    ctx->setContextObject(viewModel);

    QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/login.qml")));
    QObject *childItem = qobject_cast<QObject*>(component.create(ctx));
    //QQuickWindow *dialog = qobject_cast<QQuickWindow *>(childItem);

    //FrmAuthenticateViewModel *viewModel = new FrmAuthenticateViewModel(dialog);
    childItem->setParent(this->parent());
}

login.qml

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Layouts 1.1
import QtWebKit 3.0
//import QtWebView 1.0
import QtTest 1.0

ApplicationWindow {
    id: loginDialog
    title: qsTr("Hello World")
    width: 480
    height: 550
    visible: true

        TextField {
            id: txtUrl
            height: 30
            text: binding("sampleText");
            anchors.right: parent.right
            anchors.rightMargin: 100
            anchors.left: parent.left
            anchors.leftMargin: 0
            anchors.top: parent.top
            anchors.topMargin: 0
        }

        Button {
            id : btn1
            width: 100
            height: 30
            text: "Go"
            anchors.top: parent.top
            anchors.topMargin: 0
            anchors.right: parent.right
            anchors.rightMargin: 0
            onClicked:
            {
                text : binding("sampleText");
            }
        }
}

loginviewmodel.cpp

#include "loginviewmodel.h"

LoginViewModel::LoginViewModel(QObject *parent) : QObject(parent)
{

}

QVariant LoginViewModel::binding(const QString &propPath) const
{
    return this->property(qPrintable(propPath));
}

QVariant LoginViewModel::getAuthenCode(const QString &message) const
{
    qDebug() << message;
}

PS: "Tiếng tôi vang rừng núi... sao không ai trả lời"

[Dong]

I'm try to do everything in main.cpp like this... and it work fine.

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

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    QObject *topLevel = engine.rootObjects().at(0);
    QQuickWindow *window = qobject_cast<QQuickWindow*>(topLevel);

    LoginViewModel *viewModel = new LoginViewModel();
    viewModel->setProperty("url", "<AuthenticationUrl>");

    QQmlContext *ctx = new QQmlContext(engine.rootContext());
    ctx->setContextObject(viewModel);

    QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/login.qml")));
    QObject *childItem = component.create(ctx);
    childItem->setParent(window);

    MainWindowViewModel *mainViewModel = new MainWindowViewModel(window);
    QQmlContext *mainContext = engine.rootContext();
    mainContext->setContextObject(mainViewModel);

    return app.exec();
}

After investigation, I found out the root cause is :
QQmlApplicationEngine engine is not singleton. it completely different instance.

So, I try to keep track the engine created from the main.cpp
but QQmlApplicationEngine is Q_DISABLE_COPY
Then, I create a class (ApplicationContext) with static RootContext object to store the mainContext.

Then any time I need the "Root Engine", I get it from RootContext like this:

QQmlContext* rootContext = ApplicationContext::RootContext;
... 
QQmlComponent component(rootContext->engine(), QUrl(QStringLiteral("qrc:/login.qml")));