QML model updating without binding loops / correct behavior

centz

Hey,

Suppose I I have the following model:

ListModel {
    id: actionModel

    ListElement {
        name: "Check 1"
        text: "Performing Check 1..."
        check: function () {console.log("check1"); return true}
        status: "waiting"
    }
    ListElement {
        name: "Check 2"
        text: "Performing Check 2... "
        check: function () {console.log("check2"); return false}
        status: "waiting"
    }
    ListElement {
        name: "Check 2"
        text: "Performing Check 3..."
        check: function () {console.log("check3"); return false}
        status: "waiting"
    }
}

to be displayed by a ListView and the following delegate

Component {
    id: actionDelegate
    Item {
        width: parent.width
        height: 40
        anchors.horizontalCenter: parent.horizontalCenter

        property string myStatus: model.status
        property int myIndex: model.index
        property string myText: model.text

        function updateStatus(index, newStatus) {
            modelsContainer.actionModel.setProperty(index, "status", newStatus);
        }

        onMyStatusChanged: {
            if (myStatus === "waiting") {
                state = "waiting";
            } else if (myStatus === "running") {
                state = "running";
                var result = model.check();

                if (result) {
                    state = "passed"
                    Qt.callLater(updateStatus, myIndex, "passed")

// updateStatus(updateStatus, myIndex, "passed")
}
else {
state = "failed"
Qt.callLater(updateStatus, myIndex, "failed")
}

                if (result && myIndex < (modelsContainer.actionModel.count - 1)) {
                    Qt.callLater(updateStatus, myIndex + 1, "running");
                }

            } else if (myStatus === "passed") {
                state = "passed";
            } else if (myStatus === "failed") {
                state = "failed";
            }
        }

        states: [
            State {
                name: "waiting"
                PropertyChanges {
                    target: myTextField
                    color: "grey"
                    text: "waiting"
                }
                // Define properties and behaviors for 'waiting' state
            },
            State {
                name: "running"
                PropertyChanges {
                    target: myTextField
                    color: "blue"
                    text: "running"
                }
                // Define properties and behaviors for 'running' state
            },
            State {
                name: "passed"
                PropertyChanges {
                    target: myTextField
                    color: "green"
                    text: "passed"
                }
                // Define properties and behaviors for 'passed' state
            },
            State {
                name: "failed"
                PropertyChanges {
                    target: myTextField
                    color: "red"
                    text: "failed"
                }
                // Define properties and behaviors for 'failed' state
            }
        ]

        MyTextField {
            id: myTextField
            text: myText
            color: "grey"
        }
    }
}.

The status field/role/whatever of the ListElement is bound to a local property called myStatus through:

property string myStatus: model.status.

The intended semantics are: display the list in a waiting status. Trigger a series of checks depending on whether the previous check has completed. On pass check trigger the next. On fail stop everything.

Now an issue appears:
Writing an onMyStatusHandler results in a binding loop, if I try to to update the model synchronously when some change happens because the handler itself is also modifying the model.

I guess this is a result of trying to place the "on initial trigger logic, do the test and if that passes move to the next" inside some handler. Although offloading this to a separate function will likely also trigger a binding loop...

The intended unidirectional semantics would be:
1)capture the change
2) while handling the change break the binding(?)
3) calculate the new state <- this step must not trigger a new Change handler
4) store the new state and restore the binding.

A temporary hack is to try to (1) modify the local state on model change (2) use Qt.callLater to update the model after the handler without triggering a loop. But the solution feels hacky.

Is there a recommended API and/or solution for this problem?