C++ function exposed to QML

Hello QGC developers,
I am trying to create a new window in AnalyzeTools option, along with MavlinkInspector , vibration and everything. I have written C++ backend with Q_INVOKABLE functions and also window QML .

import QtQuick                      2.3
import QtQuick.Controls             1.2
import QtQuick.Layouts              1.2
import QtQuick.Dialogs              1.2
import QtQuick.Window               2.2
import QtCharts                     2.3

import QGroundControl               1.0
import QGroundControl.Palette       1.0
import QGroundControl.Controls      1.0
import QGroundControl.Controllers   1.0
import QGroundControl.ScreenTools   1.0

AnalyzePage {
    id:                 CustomPage
    headerComponent:    headerComponent
    pageComponent:      pageComponent
    pageDescription:    qsTr(" Application User Interface.")
    allowPopout:        true

    property int curCompID:     0
    property real maxButtonWidth: 0
    property real _margin:           ScreenTools.defaultFontPixelWidth
    property real _butttonWidth:     ScreenTools.defaultFontPixelWidth * 30


        RowLayout {
            width: availableWidth
            height: availableHeight

            Connections {
                target: CustomController

            Column {
                spacing:            _margin
                Layout.alignment:   Qt.AlignTop | Qt.AlignLeft
                    // enabled:    
                    text:       qsTr("Launch  App")
                    width:      _butttonWidth
                    onClicked: {


                    // enabled:
                    text:       qsTr("Stop  App")
                    width:      _butttonWidth
                    onClicked:  {


C++ Code. CustomController.h

// Controller for CustomPage.qml
class CustomController : public QObject{



        Q_INVOKABLE void launch       ();
        Q_INVOKABLE void stop         ();

    // private slots:  

        bool              _launched;
        Vehicle*          _vehicle;
        UASInterface*     _uas;
        QTimer            _timer;

        void _sendLauncherMessage   (uint8_t launch , uint8_t msg_type , uint8_t error_type);

In cpp file there are definitions for launch and stop functions mentioned above.
I have modified the CMakeLists.txt and also QGCApplication.cc to add

qmlRegisterType<CustomController>              (kQGCControllers,                       1 ,0, "CustomController");

This is throwing a error

 TypeError: Property 'launch' of object [object Object] is not a function.

Any possible reason why C++ functions are not exposed to QML here ?
I am very new to QT QML development . Any help would be appreciated .Thanks.

I had to create a instance of CustomController in qml file. It worked after that.