QML - signals for properties of nested objets

Richard Buchmann

In fact, I would like to read a JSON file and store it into a variable.
Ideally, components will read/write/connect to the nested properties.

I fail to connect to signals of nested properties.
I tried several approaches:

    property var test: { "a": "a value", "nested": { "inner": 5 } }
    // property alias aliasTestA: test.a  // does not compile: Invalid alias reference. Unable to find id "test"
    property var bindingTestA: test.a
    property var bindingTestNestedInner: test.nested.inner

    Connections {
        target: item
        function onTestChanged() {
            console.debug("onTestChanged", test)
        }
    }

    Connections {
        target: test
        function onAChanged() {
            console.debug("test.onFooChanged", test.a)
        }
    }

    Connections {
        target: test.nested
        function onInnerChanged() {
            console.debug("test.nested.onInnerChanged", test.nested.inner)
        }
    }

    // onAliasTestAChanged: console.debug("onAliasTestAChanged", test.a)
    onBindingTestAChanged: console.debug("onBindingTestAChanged", test.a)
    onBindingTestNestedInnerChanged: console.debug("onBindingTestNestedInnerChanged", test.nested.inner)

    Component.onCompleted: {
        test.nested.inner = 6;
        test.nested = { "inner": 7}
        test.a = "baz"
        test = { "a": "arg", "nested": { "inner": 8 } }
    }

I got:

QML Connections: Detected function "onInnerChanged" in Connections element. This is probably intended to be a signal handler but no signal of the target matches the name.
onBindingTestAChanged a value
onBindingTestNestedInnerChanged 5
onBindingTestAChanged arg
onBindingTestNestedInnerChanged 8
onTestChanged [object Object]

Adding binding for each property is not really simple and time effective.
It also miss a change: inner = 7.

Is there any tips to connect to signals in an effective way?

jeremy_k

An object must be QObject based to emit signals, whether property changes or otherwise.

Richard Buchmann

@jeremy_k Ok right!

Is there any way to convert this json object into a QObject with dynamic properties and signals?

Marko Stanke

I think the only way for you is to use a QtObject and declare properties for it:

property QtObject test: QtObject {
    property string a;
    etc...
}

jeremy_k

@Marko-Stanke said in QML - signals for properties of nested objets:

I think the only way for you is to use a QtObject and declare properties for it:
property QtObject test: QtObject {
    property string a;
    etc...
}

Yes, QML's QtObject is a QObject. Item, Rectangle, and most instantiable types know to the QML engine would also work to host properties. If you don't need any of their extra capabilities, then QtObject is the leanest QML language option.