How to avoid binding loop when binding to Python/C++ backend?

Curtwagner1984

Greetings,

I have the the following component:

main file:

InputPaneRow{
                id:sourceFolderInputRow
                Layout.preferredWidth: parent.width
                Layout.preferredHeight: parent.height * 0.5
                lableText: "Source Folder Path:"
                inputPlaceHolderText: "Please Select Folder to scan."
                inputText: gui_data.source_folder_path // <=***Binding ***
                browseButtonText: "Browse"
                openButtonText: "Open"
}

InputPaneRow.qml


Pane{
    id:inputPaneRowRoot
    property alias lableText: inputPaneRowLabel.text
    property alias inputPlaceHolderText: inputPaneRowTextField.placeholderText
    property alias inputText: inputPaneRowTextField.text <= ***binding alias***
    property alias browseButtonText: inputPaneRowBrowseButton.text
    property alias openButtonText: inputPaneRowOpenButton.text

//    background: Rectangle{
//        color: Material.color(Material.Cyan)
//    }

    signal browseButtonClicked()
    signal openButtonClicked()

    RowLayout {
        id:inputPaneRowRowLayout
        width: parent.width
        height: parent.height
        anchors.fill: parent

        Label {
            id: inputPaneRowLabel
//            font.pixelSize: parent.height * 0.45
            Layout.preferredWidth: parent.width * 0.2
//            Layout.minimumWidth: 180
        }

        TextField {
            id: inputPaneRowTextField
            Layout.preferredWidth: parent.width * 0.5
            Layout.minimumWidth: 250
        }

        Button{
            id: inputPaneRowBrowseButton
            Layout.minimumWidth: 50
            onClicked: {
                inputPaneRowRoot.browseButtonClicked()
            }
        }

        Button{
            id: inputPaneRowOpenButton
            Layout.minimumWidth: 50
            onClicked: {
                inputPaneRowRoot.openButtonClicked()
            }
        }
        Item{
            id:spacer
            Layout.fillWidth: true
        }
    }
}

There is a binding inputText: gui_data.source_folder_path where gui_data is a context property of a Python class and source_folder_path is a property (fully implmented with getter,setter and a notify signal).

This binding works when the value is set from elsewhere. But I also want any text changes in inputPaneRowTextField (Which the above inputText is an alias of will also reflect those changes back to the python class.) Meaning when the user changes/types in the textfield, the property in python should be updated.

I tried to do something like this:

InputPaneRow{
    id:sourceFolderInputRow
    inputText: gui_data.source_folder_path
    onInputTextChanged: {
        gui_data.source_folder_path = sourceFolderInputRow.inputText
    }
}

This works (even though it obviously creates a binding loop.) I guess there is a safety measure to break those kind of loops.
Question is, how do I reflect changes back to gui_data without using this. As far as I understand the initial binding should have been enough. Maybe it has something to do with aliasing?

Curtwagner1984

No one knows?

NYBL

@Curtwagner1984 said in How to avoid binding loop when binding to Python/C++ backend?:

InputPaneRow

Would be nice if you would describe what you are trying to do it is unclear what InputPaneRow is.
Anyway from what I see you want two bindings for same property is that right?
in that case you can create new property that is, say, the sum of both of them and bind to that property.
other solution would be that the getter of the python class would return the other property as well.

fcarney

Can you avoid the binding in the first place and just set on creation of the component?

InputPaneRow{
    id:sourceFolderInputRow
    //inputText: gui_data.source_folder_path
    onInputTextChanged: {
        // if a binding is involved you should be checking if it actually needs updating, only needed if using binding
        if(gui_data.source_folder_path !== sourceFolderInputRow.inputText)
            gui_data.source_folder_path = sourceFolderInputRow.inputText
    }
    Component.onCompleted: inputText = gui_data.source_folder_path
}

GrecKo

Don't use on<Property>Changed to set value back to the backend.

You need to use the special user change signal emitted by the Control.
If your control is a TextField the signal you want is textEdited, not textChanged.