QML global access to C++ class - c++

Question

My app has 3 level:
- Main Form
- Settings
- Device searching
From the main form I open others using:
var component = Qt.createComponent("qrc:/touch/content/SettingsMain.qml");
win = component.createObject(rootWindow2);
In main form I created object Network (it is C++ class)
Network{
id: net1
}
Object "net1" is accesible by other QML objects which were not invoked by above code creating component. Unfortunately, all QML objects created by using the code above do not see "net1".I need something like global object for all QML files. Any ideas?

Answer 1

You should use a singleton for that, it exists for that exact purpose:
// in main.cpp
qmlRegisterSingletonType(QUrl(QStringLiteral("qrc:/touch/content/SettingsMain.qml")), "Core", 1, 0, "Settings");
Then you can access that from every QML file by importing:
import Core 1.0
//.. and use it
Settings.someProperty
Settings.someFoo()
You would also have to add a pragma Singleton line in the beginning of SettingsMain.
You can also skip registering the singleton from C++ if you implement a qmldir file, but IMO registering in C++ is better when the singleton is an integral part of the application.
When using qml singletons, you don't need to create the instance yourself, it will be automatically created.
Your question is ambigious as to what you actually want to be "global", I assume settings is one thing you would like to be global.
You can also register C++ objects as singletons in QML, for example:
qmlRegisterSingletonType<Network>("Core", 1, 0, "Network", someFooReturningValidNetworkPtr);

Answer 2

Singleton is not the only way. QML provides lots of ways to get same results.
Another way is to pass the net1 id in as a property when calling Qt.createObject(). Example below:
main.qml
import QtQuick 2.7
import QtQuick.Controls 2.0
ApplicationWindow {
visible: true
width: 640
height: 480
Item {
id: rootWindow2
property Item settingsMain
Network{
id: net1
}
Component.onCompleted: {
var component = Qt.createComponent("qrc:/touch/content/SettingsMain.qml");
settingsMain = component.createObject(rootWindow2, {"net1": net1});
}
}
}
SettingsMain.qml
import QtQuick 2.0
Item {
property Item net1
Component.onCompleted: {
console.log("SettingsMain.qml: can I see net1? %1".arg(net1 ? "yes" : "no"))
}
}