How to keep a single instance of the window?

Question

I have the next QML:

import Qt.labs.platform 1.0

SystemTrayIcon {
    visible: true
    iconSource: "qrc:/icons/ic_tray.png"
    menu: Menu {
        MenuItem {
            text: qsTr("Settings")
            onTriggered: {
                // Don't create a new object if it exists, just show
                var settings = Qt.createComponent("main.qml")
                var form = settings.createObject(this)
                form.show()
            }
        }
        MenuItem {
            text: qsTr("Quit")
            onTriggered: Qt.quit() // Just hide an existing
        }
    }
}

How to create main.qml one time only and after just show/hide?
P.S. I'm learning Qt including QtQuick 2 only

Answer 1

Depending on how your application is structured, the best way could be to pass in the window that the tray icon shall control as a property from "further up" your user interface structure.

First, extend your tray icon component and add a "window" property to it:

import QtQuick 2.9
import QtQuick.Window 2.2
import Qt.labs.platform 1.0

SystemTrayIcon {
    id: trayIcon

    // this property holds the window the tray icon controls:
    property Window window

    visible: true

    iconSource: "qrc:/icons/ic_tray.png"
    menu: Menu {
        MenuItem {
            text: qsTr("Settings")
            onTriggered: {
                trayIcon.window.show();
            }
        }
        MenuItem {
            text: qsTr("Quit")
            onTriggered: Qt.quit() // Just hide an existing
        }
    }
}

Now, you could instantiate your tray icon e.g. in your main window like this:

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    id: mainWindow

    width: 800
    height: 600

    TrayIcon { window: mainWindow }
}

In this case, the tray icon would control the main window itself; however, you can easily create a single instance of a settings window within the main window and pass that one to the tray icon.

Answer 2

You can create the component in the onCompleted.

SystemTrayIcon {
    visible: true
    iconSource: "qrc:/icons/ic_tray.png"

    menu: Menu {
        MenuItem {
            text: qsTr("Settings")
            property var form
            onTriggered: {
                form.show()
            }
            Component.onCompleted: {
                // Don't create a new object if it exists, just show
                var settings = Qt.createComponent("Test.qml")
                form = settings.createObject(this)
            }
        }
        MenuItem {
            text: qsTr("Quit")
            onTriggered: Qt.quit() // Just hide an existing
        }
    }
}