passing the current instance of a cpp object to a Qml file stored in library

pjorourke

I am working on a project that provides a library of Qml files. Some of the Qml file utilize a cpp class to make some call. Now since I am just a library I dont have the current instance of that cpp class. So i need who ever is using my Qml file to pass me that object. I can get this to work with properties fine but var is a generic type so intelesense is not vary useful when developing the qml file for that library. Here is an example

Qml file from library

import QtQuick 2.8
import QtQuick.Controls 2.0
Button {
   // passing in cpp object here 
    property var backend: ({})
    text: backend.name
}

Qml file from app

import QtQuick 2.9
import QtQuick.Controls 2.2
import Qt.labs.platform 1.0
// Load our plugin from filesystem
import my.plugin.example 1.0 as MyPlugin
import "plugin/MyScript.js" as MyScript

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: "helloworld"

    // 'myplugin' C++ class
    MyPlugin.MyQuickItem {
        id: pluginItem
        name: "pat"
        color: "green"
        width: 100
        height: 50
        anchors.centerIn: parent
    }

    // 'myplugin' QML file
    MyPlugin.MyQml {
  // injecting my cpp class into my qml from library
        backend: pluginItem
        anchors.top: pluginItem.bottom
        anchors.horizontalCenter: pluginItem.horizontalCenter
        width: pluginItem.width
        onClicked: {
            MyScript.onClicked(pluginItem);
        }
    }

    Button
    {
        width: 50
        height: 50
        text: pluginItem.itemName
    }
}

this works perfectly fine but when developing intelesense would be nice so I was looking for a way to convert the property var to the specific type. then use the specific type in the qml file. here is my stab at it with no luck.

import QtQuick 2.8
import QtQuick.Controls 2.0
import my.plugin.example 1.0 as MyPlugin
Button {
    property var backend: itemMy
    MyPlugin.MyQuickItem
    {
        id: itemMy
    }
   
    text: itemMy.name
}

any help would be much appericated

sierdzio

property var backend: itemMy

At the very least you can make your backend variable a QtObject:

property QtObject backend: null

Since we are talking about a library, you probably expect (require) backend to have some properties, methods etc. right? Then you need to define such C++ class in your library, to act as a base class (interface) for users of your library. Then you can register your base class with QML (qmlRegisterType() etc.) and use it in QML:

property MyInterfaceClass backend: null