QtObject singleton and Settings

Bob64

I have some application wide settings stored in a QtObject singleton object. I wanted to expose one of these as a persistent setting by extending an existing Settings object that I already use for main window size and position.

GlobalSettings.qml in root qml directory:

pragma Singleton

QtObject {
    property bool mySetting: false
    ...
}

main.qml in same directory:

...
import "."

ApplicationWindow {
    ...
    Settings {
        ...
        property alias mySetting: GlobalSettings.mySetting
    }
}

The application fails at startup with an error message:

Invalid alias reference. Unable to find id "GlobalSettings"

Is the issue simply that it is not possible to alias a singleton property like this?

Is there an obvious way around this? I could introduce a boolean property in the ApplicationWindow perhaps and alias that in the Settings, but the issue is that the boolean in question can be adjusted from a few places (menus and suchlike) and this is currently handled quite cleanly via the singleton. It would be awkward to route everything via a new ApplicationWindow property.

mzimmers

@Bob64 did you put your GlobalSettings.qml in your CMakeLists.txt file?

set_source_files_properties(
    GlobalSettings.qml
    PROPERTIES QT_QML_SINGLETON_TYPE TRUE

Bob64

@mzimmers I am using qmake. Note that there is no problem in general in using my GlobalSettings object - it has been in use for a couple of years. The problem is trying to persist one particular property in the GlobalSettings QtObject via a property alias in my Settings object.

Sorry I realise I should have chosen better names here. Just to be totally clear, Settings is a built in QML type that can be used to implement persistence of various application properties such as window sizes and so on. GlobalSettings is the singleton QtObject that is specific to my application and contains various attributes that are queried throughout the application.

The issue is that I have one specific property in GlobalSettings that I also want to persist via Settings. The standard way to do use Settings is to add a property to it which is a property alias to the actual value you want to persist. The reason it is not working for me is that the property alias to the QtObject property causes a run time error that aborts the application.