Connect to the signal from an object created by stackview.push in QML

James A

item = stackView.push("ChargeInfo.qml")
item.chrgCntrlClicked.connect(mouse_chg_control.onClicked)

connection between signals and slots is not working , getting error message
Error: Invalid write to global property "item"

Expected result : when mouse is clicked in the ChargeInfo.qml file it should emit chrgCntrlClicked signal and call the slot in batteryinfo.qml file which prints message "button clicked"

Is something wrong in connecting the signals and slots in the above example ?

Regards,
James A

jeremy_k

@James-A said in Connect to the signal from an object created by stackview.push in QML:

Hai @jeremy_k
item = stackView.push("ChargeInfo.qml")
item.chrgCntrlClicked.connect(mouse_chg_control.onClicked)
connection between signals and slots is not working , getting error message
Error: Invalid write to global property "item"

The error message is telling you that assigning to item is invalid, and is throwing an exception. The line after the assignment isn't executed. That's a limitation of the QML engine. item needs to be declared as a local var, or a non-global property.
https://doc.qt.io/qt-5/qtqml-javascript-hostenvironment.html#javascript-environment-restrictions

James A

Hai @jeremy_k

I declared the "item" as local variable as shown below, now the error does not appear , but the "mouse_chg_control.onClicked" slot in BatteryInfo.qml file is not called on emitting the "chrgCntrlClicked" in ChargerInfo.qml file.

Added the updated code below

"BatteryInfo.qml" 

Rectangle {

    Button {
        id: mouse_batInfo
        x: 207
        y: 176
        text: qsTr("Load")
        onClicked: {
            var item = stackView.push("qrc:/ChargerInfo.qml")
            item.chrgCntrlClicked.connect(mouse_chg_control.onClicked)
        }
    }

    Button {
        id: mouse_chg_control
        x: 216
        y: 277
        text: qsTr("Button")

        onClicked: {
            console.log("Button clicked")
        }
    }

}

"ChargerInfo.qml"

Rectangle{

    id: root
    signal chrgCntrlClicked

    Button {
        id: button
        x: 112
        y: 129
        text: qsTr("Button")
        onClicked: {
            root.chrgCntrlClicked
        }
    }


}

"main.qml"

ApplicationWindow {

    width: 640

    height: 480

    visible: true

    title: qsTr("Hello World")

    StackView{
      id : stackView
      initialItem: "qrc:/BatteryInfo.qml"
      anchors.fill: parent
    }

}

jeremy_k

@James-A said in Connect to the signal from an object created by stackview.push in QML:

            root.chrgCntrlClicked

This is missing () to invoke the signal.

As a matter of personal taste, I prefer using Connections over imperative javascript to manage connection to a fixed number of dynamically created objects. Both versions of StackView have a currentItem that points to the top of the stack.

James A

Hi @jeremy_k ,

Sorry for the delayed reply , the root.chrgCntrlClicked() code helped me to fix the issue. Now I am trying with Repeaters as shown in the below code.

// BatteryInfo qml file

RowLayout {
            anchors.fill: parent
            Repeater{
                id: repeater
                model : [ batteryInfo.bat1 , batteryInfo.bat2 , batteryInfo.bat3 ]

                Battery {

                    Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter

                    mouse_batInfo.onClicked: {
                        var item = stackView.push("ChargeInfo.qml")
			item.chrgCntrlClicked.connect(mouse_chg_control.onClicked)
                    }

                    mouse_chg_control.onClicked: {
                       console.log("Button is clicked")                 
                    }



                }
            }
        }

// ChargeInfo.qml file

 signal chrgCntrlClicked
 
 Repeater{

            model : [ batteryInfo.bat1 , batteryInfo.bat2 , batteryInfo.bat3 ]

            // loader is used keep only current item on the screen and load the other UI dynamically on swiping
            Loader {
                active: SwipeView.isCurrentItem
                sourceComponent: Rectangle{
                    ChargeInfoForm {
                        id: chargeInfoForm

                        mouse_chg_control.onClicked: {
                             root.chrgCntrlClicked()
                        }

                        txt_batName.text: "Battery " + (index + 1)

                    }
                }
            }

        }

Totally three Items will be created on the UI. Whenever the button is clicked the mouse_chg_control.onClicked function gets called, which has to call the corresponding slot in the Battery info qml file

But When I click the button in the ChargeInfo.qml file I get error "Error: Insufficient arguments".
What is proper way to connect the ChargeInfo.qml signal to corresponding BatteryInfo.qml slots ?

jeremy_k

@James-A Can you convert the code into a self-contained minimal example? Its easier to spot and fix errors if the code is otherwise executable.

James A

Hi @jeremy_k ,

I was able to fix the "Error: Insufficient arguments". error. Now I need some idea on how to connect the signal from an Item in the child to parent item

The BatteryInfo.qml (parent) and ChargerInfo.qml (child) contains 3 items. In child page whenever a button is clicked under an item the corresponding parent item button needs to be called. This is happening with the present code added below.
But the problem is when I swipe and click the Items button in the child page the corresponding parent item button is not called

Please execute this code to see the behaviour

// main.qml

import QtQuick 2.4
import QtQuick.Window 2.4
import QtQuick.Controls 1.4

ApplicationWindow {

    width: 700

    height: 480

    visible: true

    title: qsTr("Hello World")

    StackView{
      id : stackView
      initialItem: "qrc:/BatteryInfo.qml"
      anchors.fill: parent
    }

}

//Charge.qml

import QtQuick 2.4
import QtQuick.Controls 2.3

Rectangle{

    id: root
    width: 235
    height: 370

    property alias mouse_chg_control: mouse_chg_control
    property alias text1: text1

    Button {
        id: mouse_chg_control
        x: 87
        y: 216
        text: qsTr("Button")

    }

    Text {
        id: text1
        x: 118
        y: 116
        text: qsTr("Text")
        font.pixelSize: 12
    }


}

// Battery.qml

import QtQuick 2.2
import QtQuick.Shapes 1.2
import QtQuick.Controls 2.2
import QtQuick.Layouts 1.0

Rectangle {
    width: 235
    height: 370
    property alias txt_name: txt_name
    property alias mouse_batInfo: mouse_batInfo
    property alias mouse_chg_control: mouse_chg_control

    MouseArea {
        id: mouse_batInfo
        anchors.fill: parent
    }

    Button {
        id: mouse_chg_control
        x: 59
        y: 228
        width: 100
        height: 37
        text: qsTr("Button")
    }

    Text {
        id: txt_name
        x: 97
        y: 121
        text: qsTr("Text")
        font.pixelSize: 12
    }
}

//BatteryInfo.qml

import QtQuick 2.4
import QtQuick.Controls 2.3
import QtQuick.Layouts 1.2

Item {

    RowLayout {
        anchors.fill: parent
        Repeater{
            id: repeater
            model : 3

            Battery {

                Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter

                txt_name.text: index

                mouse_batInfo.onClicked: {
                    var item = stackView.push("qrc:/ChargeInfo.qml" ,{currentIndex : index})
                    item.chrgCntrlClicked.connect(mouse_chg_control.onClicked)
                }

                mouse_chg_control.onClicked: {
                    console.log("button clicked : " + index )
                }

            }
        }
    }

}

// ChargeInfo.qml

import QtQuick 2.4
import QtQuick.Controls 2.3
import QtQuick.Layouts 1.2

Item {

    id : chargeinfo
    property alias currentIndex : swipeView.currentIndex

    PageIndicator {
        id: indicator
        x: 485
        y: 453
        width: 50
        z: 1
        anchors.horizontalCenterOffset: 8
        anchors.horizontalCenter: swipeView.horizontalCenter
        currentIndex: swipeView.currentIndex
        count: swipeView.count
    }

    signal chrgCntrlClicked

    SwipeView{
        id: swipeView
        width: 650

        anchors.left: parent.left
        anchors.top: parent.top
        anchors.bottom: parent.bottom
        anchors.horizontalCenterOffset: 0
        anchors.leftMargin: 0
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.bottomMargin: 0
        anchors.topMargin: 71

        Repeater{

            model : 3

            // loader is used keep only current item on the screen and load the other UI dynamically on swiping
            Loader {
                active: SwipeView.isCurrentItem
                sourceComponent:
                    Rectangle{
                    Charger {

                        width: parent.width
                        anchors.horizontalCenter: parent.horizontalCenter

                        text1.text: index

                        mouse_chg_control.onClicked: {
                            chargeinfo.chrgCntrlClicked()
                        }

                    }
                }
            }
        }
    }

    Button{

        text: "BACK"

        onClicked: {

            if (stackView.depth > 1) {
                stackView.pop()
            }

        }
    }

}

jeremy_k

Lets start from a simpler example:

main.qml:

import QtQuick 2.4
import QtQuick.Controls 1.4

ApplicationWindow {
    width: 700
    height: 480
    visible: true

    StackView{
      id : stackView
      initialItem: A{}
      anchors.fill: parent
    }

    Connections {
        target: stackView.currentItem
        function onClicked() { console.log("got a click"); }
    }
}

A.qml:

import QtQuick 2.2
import QtQuick.Controls 2.2

Rectangle {
    id: root
    signal clicked()
    Button {
        anchors.centerIn: parent
        text: "button"
        onClicked: root.clicked()
    }
}

James A

Hai @jeremy_k ,

Using target: stackView.currentItem was a good idea. I tried running , its working fine.
But if there are A , B , C (child) qml files. and three onClicked slots for each child in main qml file , how to connect corresponding signals from child to main qml file

child.qml || main.qml

A.qml --> onAClicked()
B.qml --> onBClicked()
C.qml --> onCClicked()

jeremy_k

@James-A said in Connect to the signal from an object created by stackview.push in QML:

But if there are A , B , C (child) qml files. and three onClicked slots for each child in main qml file , how to connect corresponding signals from child to main qml file

Do you expect to interact with all three at the same time, or only the item currently at the top of the stack?

James A

@jeremy_k

Only with one item which is currently at the top of the stack

jeremy_k

@James-A said in Connect to the signal from an object created by stackview.push in QML:

@jeremy_k

Only with one item which is currently at the top of the stack

Then there's no need to deal each item individually. As long as all three use signals with the same name, Connections { target: stackView.currentItem } will rebind to the new currentItem, and make the connection.

James A

@jeremy_k

I updated the BatteryInfo.qml class as shown below

import QtQuick 2.4
import QtQuick.Controls 2.3
import QtQuick.Layouts 1.2

Item {

    Connections {
        target: stackView.currentItem
        function onChrgCntrlClicked()
        { console.log("got a click");
          battery.mouse_chg_control.clicked()
        }
    }

    RowLayout {
        anchors.fill: parent
        Repeater{
            id: repeater
            model : 3

            Battery {
                id : battery
                Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter

                txt_name.text: index

                mouse_batInfo.onClicked: {
                    stackView.push("qrc:/ChargeInfo.qml" ,{currentIndex : index})
                }

                mouse_chg_control.onClicked: {
                    console.log("button clicked : " + index )
                }

            }
        }
    }

}

I was getting the below error message

qrc:/BatteryInfo.qml:7:5: QML Connections: Detected function "onChrgCntrlClicked" in Connections element. This is probably intended to be a signal handler but no signal of the target matches the name.
qml: got a click
qrc:/BatteryInfo.qml:11: ReferenceError: battery is not defined

jeremy_k

@James-A said in Connect to the signal from an object created by stackview.push in QML:

@jeremy_k

I updated the BatteryInfo.qml class as shown below
[...]

There is nothing with the id stackView here. It's too confusing for me to attempt to stitch together code from previous posts and infer missing portions. Please use examples that are both simple and complete. Remove everything that is not related to the problem at hand, and include everything that a reader would need to copy and paste to achieve the same result.

I was getting the below error message

qrc:/BatteryInfo.qml:7:5: QML Connections: Detected function "onChrgCntrlClicked" in Connections element. This is probably intended to be a signal handler but no signal of the target matches the name.
qml: got a click
qrc:/BatteryInfo.qml:11: ReferenceError: battery is not defined

These are both generally straight forward errors. Is there a chrgCntrlClicked signal associated with stackView.currentItem? Is it a signal of a child item that needs to be propagated, or is there a typo? Setting the ignoreUnknownSignals property to allow for transitory states that lack the signal can help to silence irrelevant warnings.

Is there a battery property or variable in scope? Ids in a Repeater or ListView delegate are not meaningful outside of a delegate instance. The example above has 3 instances of Battery called battery created in a Repeater. Which one is battery supposed to reference?