How to declare a qml list containing both new, declared, and existing items?

lcoudeville

I'm writing a state machine in qml that shares some PropertyChanges objects over the different states. To avoid duplicate code, I store the shared PropertyChanges instances as private properties that can be mentioned several times. Items that are only used once should be declared as part of the qml list/array.

What I'm trying to do

Button {
   property PropertyChanges xxx: PropertyChanges {
      target: grs1
      color: 'red'
      restoreEntryValues: true
  }

  states: [
      State {
          name: "State A"
          changes: [ xxx ]
      }
      State {
          name: "State B"
          changes: [ xxx, PropertyChanges { target: grs1, text: "state B!" } ]
      }
   ]
}

However this code doesn't work and generates the warning/error message Expected token `,'

The question is, is it possible to declare a list containing both new defined objects and existing instances? How does that syntax look?

jeremy_k

@lcoudeville said in How to declare a qml list containing both new, declared, and existing items?:

        changes: [ xxx, PropertyChanges { target: grs1, text: "state B!" } ]

However this code doesn't work and generates the warning/error message Expected token `,'

Is there no line number reported?

Try changing: target: grs1, text: "state B!"
to: target: grs1; text: "state B!"

lcoudeville

@jeremy_k, the reported line number points to the line where the PropetyChanges is inline defined:

changes: [ xxx, PropertyChanges { target: grs1, text: "state B!" } ]

Changing to

changes: [ xxx, PropertyChanges { target: grs1; text: "state B!" } ]

did not help :-(

The first '{' on that line is highlighted by qt creator.

jeremy_k

This looks like a bug. changes can either be a list of inline Change elements, or a list accessed by id or a property. The error message changes depending on the order. With an id first, it complains about missing a , for inline elements. With an inline element first, it complains about a missing { for ids.

import QtQuick 2.15
import QtQuick.Window 2.15

Window {

    MouseArea { anchors.fill: parent; onClicked: text.nextState() }

    Text {
        id: text
        anchors.centerIn: parent
        text: "click to change"
        PropertyChanges { id: a; target: text; color: 'red' }
        PropertyChanges { id: b; target: text; text: "State B" }
        state: "a"
        states: [
            State {
                name: "a"
                changes: [
                    PropertyChanges { target: text; text: "State A" },
                    PropertyChanges { target: text; color: "blue" }
                ]
            },
            State {
                name: "b"
                changes: [ a, b ]
            },
            State {
                name: "c"
                // The next line causes a syntax error
                changes: [ PropertyChanges{ target: text; text: "State C" }, a ]
            }
        ]

        function nextState() {
            for (var i = 0; i < states.length; i++) {
                if (state === states[i].name) {
                    state = states[(i + 1) % states.length].name;
                    return;
                }
            }
        }
    }
}

That said, I don't think I have ever seen a code base attempt to reuse a PropertyChange in this way. Organizing into base states that contain the common changes, and extended states that customize is usually the way it's done. With a *Change inline in a State, there no need to even mention changes