How to avoid QML error: “This is probably intended to be a signal handler but no signal of the target matches the name.”

rhvonlehe

I have working QML that has an ApplicationWindow with a Loader. The loader has a default qml file GameStart.qml representing a screen with some startup activities. For simplicity, say the 1st screen can navigate to the 2nd screen gamePlay.qml and the 2nd can navigate back to the 1st. The navigation is done by the loaded item emitting a signal that the ApplicationWindow has slots for. All that happens in the slots is the Loader's source gets modified.

// RootWindow.qml
import QtQuick          2.12
import QtQuick.Controls 2.12
import QtQuick.Window   2.12
import QtQuick.Layouts  1.12
ApplicationWindow {
    id:             mainWindow
    minimumWidth:   Math.min(215 * Screen.pixelDensity, Screen.width)
    minimumHeight:  Math.min(120 * Screen.pixelDensity, Screen.height)
    visible:        true
    color:          "turquoise"

    property string currentScreen: "GameStart.qml"

    Loader {
        id:             dynamicLoader
        anchors.fill:   parent
        source:         currentScreen
    }

    Connections {
        target: dynamicLoader.item
        function onPlayGame() {
            currentScreen = "GamePlay.qml"
            console.log("currentScreen: ", currentScreen)
        }
    }
    Connections {
        target: dynamicLoader.item
        function onEndGame() {
            currentScreen = "GameStart.qml"
            console.log("currentScreen: ", currentScreen)
        }
    }
}

The default screen and the other screen declare signals like this:

// GameStart.qml
import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12

Item {
    id: gameStart
    anchors.top: parent.top
    height: parent.height
    width: parent.width
    signal playGame

    RowLayout {
        id: layout
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter

        RoundButton {
            id: playButton
            text: "Play"
            width: 40
            radius: 2
            font.pointSize: 12
            Layout.alignment: Qt.AlignVCenter
            onClicked: {
//                var players = selector.playerArray
//                for (var i =0; i < players.count; i++) {
//                    console.log(players.itemAt(i).playerName)
//                    game.addPlayer(players.itemAt(i).playerName)
//                }
                gameStart.playGame()
            }
        }
    }
}

Things work the way I expect them to, but there is a runtime error message that pops up that I'd rather not have:

qrc:/qml/RootWindow.qml:25:5: QML Connections: Detected function "onPlayGame" in Connections element. This is probably intended to be a signal handler but no signal of the target matches the name.

My guess is this happens because I use as the Connections target: dynamicLoader.item and that is not a specific object id, but rather a dynamically loaded object. I am not able to use e.g. gameStart or gamePlay as targets of the Connections in RootWindow.qml, however. Those IDs are not recognized within that file.

I suspect I have not discovered the idiomatic way of doing this and my way is kludgey. What should I do to avoid this runtime message?

EDIT: here's the GamePlay.qml file and also PlayerArea.qml

//GamePlay.qml
import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12
import QtQml.Models 2.12
import QtQml 2.12


Item {
    id: gamePlay
    signal endGame
    property var playerArray : game.getPlayers()

    ListModel {
        id: playerLayoutModel
        ListElement {
            property var row: 1
            property var column: 0
        }
        ListElement {
            property var row: 1
            property var column: 2
        }
        ListElement {
            property var row: 0
            property var column: 1
        }
        ListElement {
            property var row: 2
            property var column: 1
        }
    }

    ColumnLayout {
        id: mainColumn
        spacing: 2
        anchors.fill: parent
        anchors.horizontalCenter: parent.horizontalCenter

        Rectangle {
            Layout.alignment: Qt.AlignHCenter
            height: 100
            width: 250
            color: "turquoise"
            RowLayout {
                id: gameButtonsLayout
                anchors.fill: parent
                Button {
                    id: deal
                    Layout.preferredHeight: 50
                    Layout.preferredWidth: 80
                    text: "Deal"
                }

                Button {
                    id: end
                    Layout.preferredHeight: 50
                    Layout.preferredWidth: 80
                    text: "End Game"
                    onClicked: {
                        gamePlay.endGame()
                    }
                }

                Button {
                    id: save
                    Layout.preferredHeight: 50
                    Layout.preferredWidth: 80
                    text: "Save Game"
                }
            }
        }

        Rectangle {
            Layout.fillHeight: true
            Layout.fillWidth: true
            anchors.horizontalCenter: Layout.horizontalCenter
            color: "turquoise"

            GridLayout {
                id: gridnew
                columns: 3
                rows: 3
                anchors.fill: parent
                property var playerCnt: playerArray.length

                Repeater {
                    model: playerLayoutModel
                    delegate: playerArea
                }

                Component {
                    id: playerArea
                    PlayerArea {
                        color: "red"
                        playerName: playerArray[index]
                        Layout.row: model.row
                        Layout.column: model.column
                        Layout.fillHeight: true
                        Layout.fillWidth: true
                        enabled: gridnew.playerCnt > index ? true : false
                        opacity: gridnew.playerCnt > index ? true : false
                    }
                }
            }

            Component.onCompleted: {
                console.log("rectangle containing grid size: ", height, width)
                console.log("rectangle center: ", horizontalCenter, verticalCenter)
            }
        }
    }

}

// GamePlay.qml
import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Layouts 1.12

Item {
    id: playerArea
    property string playerName
    property string cardText
    property string color

    Component.onCompleted: {
        var globalCoords = playerArea.mapToItem(gamePlay, x, y)
        console.log("playerArea.enabled: ", enabled)
        console.log("playerArea coords: ", x, y)
        console.log("area at coords: ", globalCoords.x, globalCoords.y)
    }

    ColumnLayout {
        //        Card {
        //        }

        //        Rectangle { // TODO remove when graphical card ready
        //            height: 20
        //            width: 20
        anchors.horizontalCenter: parent.horizontalCenter
        Label {
            color: playerArea.color
            height: 50
            width: 50
            text: cardText
        }
        //        }


        Label {
            id: nameLabel
            height: 50
            width: 50
            text: playerName
        }

        Button {
            id: playButton
            height: 50
            width: 50
            text: "Play Card"
        }
    }

}

jeremy_k

@rhvonlehe https://doc.qt.io/qt-6/qml-qtqml-connections.html#ignoreUnknownSignals-prop

While the Loader is loading, Loader.item doesn't point to a valid object. As such, the signal expected by the Connections instance also won't exist.

rhvonlehe

I wouldn't have thought there would be a property to ignore a runtime error message. It definitely works, though. Thank you.

There's a similar Stack Overflow message that you can answer and take credit for there if you like. I can't answer it myself for a day or two.

jeremy_k

@rhvonlehe said in How to avoid QML error: “This is probably intended to be a signal handler but no signal of the target matches the name.”:

I wouldn't have thought there would be a property to ignore a runtime error message.

That's what Connections.ignoreUnknownSignals is. "If this property is set to true, such errors are ignored."
Logging the condition, depending on the Qt Declarative version, is implemented as:

        } else if (!d->ignoreUnknownSignals
                               && propName.startsWith(QLatin1String("on")) && propName.length() > 2
                               && propName.at(2).isUpper()) {
                        qmlWarning(this) << tr("Detected function \"%1\" in Connections element. "
                                               "This is probably intended to be a signal handler but no "
                                               "signal of the target matches the name.").arg(propName);
                    }

Or do you mean ignore warning messages in general? QLoggingCategory configuration can do that, as can qInstallMessageHandler.

There's a similar Stack Overflow message that you can answer and take credit for there if you like. I can't answer it myself for a day or two.

I never got into Stack Overflow point collecting. Thanks for the offer.

rhvonlehe

@jeremy_k
"I never got into Stack Overflow point collecting. Thanks for the offer."

I like you even more now.

Marked as solved. I forgot to do this yesterday.