Correct way to do test for null in QML?

[SPlatten]

In QML I have a property:

    id: root
    property var anchorHorzCenter: parent.anchors.horizontalCenter
    property var anchorTop: parent.anchors.top

Usage in the same QML:

    Text {
        id: rText
        anchors.horizontalCenter: {
            if ( root.anchorHorzCenter !== 0 ) {
                return root.anchorHorzCenter
            }
        }
        anchors.top: {
            if ( root.anchorTop !== 0 ) {
                return root.anchorTop
            }
        }

This can't correct because when I run the application I get:

qrc:/StaleDataModel.qml:41:5: QML QQuickText: Cannot anchor to a null item. qrc:/StaleDataModel.qml: 41

[SPlatten]

@SPlatten , SOLVED:

StaleDataModel.qml:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Item {
    id: root
    property var fontPointSize: 16
    property string label
    property string labelColor: "#FF000000"
    property var percision: 4
    property real textWidth: 80
    property var value: simonP.value

    function checkStaleStatus(strToolTip) {
        if ( typeof strToolTip != "string" ) {
            simonP.stale()
            return
        }
        rImage.ToolTip.text = strToolTip
        rImage.visible = (strToolTip.length > 0)

        if ( rImage.visible === true ) {
            rText.color = simonP.strStale()
        } else {
            rText.color = simonP.strNormal()
        }
    }
    function rad2Deg(rad_) {
      return rad_ * 180.0 /  Math.PI;
    }
    function setPrecision (val_, sigDigit_) {
        var precision = Math.abs (val_) >= 1000 ? sigDigit_ - 4 :
        Math.abs (val_) >= 100 ? sigDigit_ - 3 :
        Math.abs (val_) >= 10 ? sigDigit_ - 2 :
        2;

      if (precision < 0)
        precision = 0;

      return val_.toFixed (precision);
    }
    function setValue(newValue) {
        simonP.setValue(newValue)
        rText.text = setPrecision (newValue, percision)
    }

    StaleData {
        id: simonP
        onValueChanged: {
            checkStaleStatus(strToolTip)
        }
    }

    Text {
        id: rText
        anchors {
            right: root.right
            top: root.top
        }
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignRight
        font.pointSize: 16//root.fontPointSize
        text: {
            root.value
                ? String(setPrecision (rad2Deg (root.value), percision))
                : "N/A"
        }
        width: root.textWidth
    }

    Label {
        id: rLabel
        text: root.label
        anchors.top: rText.bottom
        anchors.right: rText.right
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignRight
        font.pointSize: root.fontPointSize
        color: root.labelColor
    }

    Image {
        id: rImage
        anchors {
            right: rLabel.left
            top: rLabel.top
        }
        visible:  false
        source: "/stale.svg"
        ToolTip.visible: (rImage.visible && ToolTip.text.length) > 0 && ma.containsMouse

        MouseArea {
            id: ma
            anchors.fill: parent
            hoverEnabled: true
            onContainsMouseChanged: checkStaleStatus()
        }
    }

    Timer {
        interval: 250
        running: true
        repeat: true
        onTriggered: simonP.stale()
    }
}

Usage:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Window {
    id: root
    visible: true
    width: 640
    height: 480
    title: qsTr("Playground / Staging Arena")

    StaleDataModel {
        id: hdg
        label: "HDG"
        anchors {
            right: parent.right
            top: parent.top
        }
        fontPointSize: parent.width < 150 ? 30 : 16
        textWidth: 256
    }

    Button {
        id: btnData
        text: "Click Me..."
        anchors {
            left: parent.left
            top: parent.top
        }
        onClicked: {
            hdg.setValue(parseFloat(hdg.value) + 0.01);
        }
    }
}

[JoeCFD]

@SPlatten said in Correct way to do test for null in QML?:

        if ( root.anchorHorzCenter !== 0 ) {
            return root.anchorHorzCenter
        }

this is not a function why return?
anchors.horizontalCenter: {
if ( root.anchorHorzCenter !== 0 ) {
return root.anchorHorzCenter
} you need else as well?
}

[J.Hilk]

@SPlatten

anchors.horizontalCenter:  root.anchorHorzCenter ? root.anchorHorzCenter : undefined

[fcarney]

@J-Hilk said in Correct way to do test for null in QML?:

anchors.horizontalCenter: root.anchorHorzCenter ? root.anchorHorzCenter : undefined

I addition to this, if you are running 5.15 and above, you can do nullish operator too:

anchors.horizontalCenter:  root.anchorHorzCenter ?? undefined

[SPlatten]

This is the QML I have:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Item {
    id: root
    property var fontPointSize: 30
    property string label
    property var percision: 4
    property real textWidth: 80
    property var value: simonP.value

    function checkStaleStatus(strToolTip) {
        if ( typeof strToolTip != "string" ) {
            simonP.stale()
            return
        }
        rImage.ToolTip.text = strToolTip
        rImage.visible = (strToolTip.length > 0)

        if ( rImage.visible === true ) {
            rText.color = simonP.strStale()
        } else {
            rText.color = simonP.strNormal()
        }
    }
    function rad2Deg(rad_) {
      return rad_ * 180.0 /  Math.PI;
    }
    function setPrecision (val_, sigDigit_) {
        var precision = Math.abs (val_) >= 1000 ? sigDigit_ - 4 :
        Math.abs (val_) >= 100 ? sigDigit_ - 3 :
        Math.abs (val_) >= 10 ? sigDigit_ - 2 :
        2;

      if (precision < 0)
        precision = 0;

      return val_.toFixed (precision);
    }
    function setValue(newValue) {
        simonP.setValue(newValue)
        rText.text = setPrecision (newValue, percision)
    }

    StaleData {
        id: simonP
        onValueChanged: {
            checkStaleStatus(strToolTip)
        }
    }

    Text {
        id: rText
        anchors {
            top: parent.top
            right: parent.right
        }
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignLeft
        font.pointSize: root.fontPointSize
        text: { root.value
                ? String(setPrecision (rad2Deg (root.value), percision))
                : "N/A"
        }       
        width: root.textWidth
    }

    Label {
        id: rLabel
        text: root.label
        anchors.top: rText.bottom
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignLeft
        font.pointSize: root.fontPointSize
        width: parent.width
        color: "#FF000000"
    }

    Timer {
        interval: 250
        running: true
        repeat: true
        onTriggered: simonP.stale()
    }

    Image {
        id: rImage
        visible:  false
        anchors.left: rText.right
        source: "/stale.svg"
        ToolTip.visible: ToolTip.text.length > 0 && ma.containsMouse

        MouseArea {
            id: ma
            anchors.fill: parent
            hoverEnabled: true
            onContainsMouseChanged: checkStaleStatus()
        }
    }
}

Usage:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Window {
    id: root
    visible: true
    width: 640
    height: 480
    title: qsTr("Playground / Staging Arena")

    StaleDataModel {
        id:hdg
        label: "HDG"
        anchors {
            left: parent.left
            top: parent.top
        }
        fontPointSize: parent.width < 150 ? 30 : 16
        textWidth: 256
    }

    Button {
        id: btnData
        text: "Click Me..."
        anchors.top: hdg.anchors.bottom
        onClicked: {
            hdg.setValue(parseFloat(hdg.value) + 0.01);
        }
    }
}

What I want to achieve is the data over the label with the icon to the right of the data label. What I actually get is the icon under the label and no data showing at all.

[SPlatten]

@SPlatten , SOLVED:

StaleDataModel.qml:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Item {
    id: root
    property var fontPointSize: 16
    property string label
    property string labelColor: "#FF000000"
    property var percision: 4
    property real textWidth: 80
    property var value: simonP.value

    function checkStaleStatus(strToolTip) {
        if ( typeof strToolTip != "string" ) {
            simonP.stale()
            return
        }
        rImage.ToolTip.text = strToolTip
        rImage.visible = (strToolTip.length > 0)

        if ( rImage.visible === true ) {
            rText.color = simonP.strStale()
        } else {
            rText.color = simonP.strNormal()
        }
    }
    function rad2Deg(rad_) {
      return rad_ * 180.0 /  Math.PI;
    }
    function setPrecision (val_, sigDigit_) {
        var precision = Math.abs (val_) >= 1000 ? sigDigit_ - 4 :
        Math.abs (val_) >= 100 ? sigDigit_ - 3 :
        Math.abs (val_) >= 10 ? sigDigit_ - 2 :
        2;

      if (precision < 0)
        precision = 0;

      return val_.toFixed (precision);
    }
    function setValue(newValue) {
        simonP.setValue(newValue)
        rText.text = setPrecision (newValue, percision)
    }

    StaleData {
        id: simonP
        onValueChanged: {
            checkStaleStatus(strToolTip)
        }
    }

    Text {
        id: rText
        anchors {
            right: root.right
            top: root.top
        }
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignRight
        font.pointSize: 16//root.fontPointSize
        text: {
            root.value
                ? String(setPrecision (rad2Deg (root.value), percision))
                : "N/A"
        }
        width: root.textWidth
    }

    Label {
        id: rLabel
        text: root.label
        anchors.top: rText.bottom
        anchors.right: rText.right
        verticalAlignment: Text.AlignTop
        horizontalAlignment: Text.AlignRight
        font.pointSize: root.fontPointSize
        color: root.labelColor
    }

    Image {
        id: rImage
        anchors {
            right: rLabel.left
            top: rLabel.top
        }
        visible:  false
        source: "/stale.svg"
        ToolTip.visible: (rImage.visible && ToolTip.text.length) > 0 && ma.containsMouse

        MouseArea {
            id: ma
            anchors.fill: parent
            hoverEnabled: true
            onContainsMouseChanged: checkStaleStatus()
        }
    }

    Timer {
        interval: 250
        running: true
        repeat: true
        onTriggered: simonP.stale()
    }
}

Usage:

import QtQuick 2.0
import QtQuick.Controls 2.15
import QtQuick.Controls.Styles 1.4
import QtQuick.Layouts 1.3
import QtQuick.Extras 1.4
import QtQuick.Window 2.12
import SimonsCPP 1.0

Window {
    id: root
    visible: true
    width: 640
    height: 480
    title: qsTr("Playground / Staging Arena")

    StaleDataModel {
        id: hdg
        label: "HDG"
        anchors {
            right: parent.right
            top: parent.top
        }
        fontPointSize: parent.width < 150 ? 30 : 16
        textWidth: 256
    }

    Button {
        id: btnData
        text: "Click Me..."
        anchors {
            left: parent.left
            top: parent.top
        }
        onClicked: {
            hdg.setValue(parseFloat(hdg.value) + 0.01);
        }
    }
}