Interfacing qml and c++

[JennyAug13]

Hello I am trying to change the property in qml file using some c++ code.
But when i build it, it is giving following errors.

The program has unexpectedly finished.
"QQmlComponent:Component is not ready". Here is my code.

void NTUserSettingsModel::installPulseWidthToFrequencyHandler()
{
    NTUserSetting * pulseWidth = m_settingsMap.value(NTUserSetting::ID_PULSE_WIDTH);
    NTUserSetting * frequency  = m_settingsMap.value(NTUserSetting::ID_FREQUENCY);

    qCDebug(LC_NTUserSettingsModel())<< "pulseWidth is changed";
    QQmlEngine engine;
    QQmlComponent component(&engine, QUrl(QStringLiteral("Sources/QmlSources.qrc:/QML/Components/NTSpinBox.qml")));
    QObject *object = component.create();
    object->setProperty("color","white");
    delete object;

    if(pulseWidth && frequency)
    {
      connect(pulseWidth, &NTUserSetting::beforeValueChanged,   this,      &NTUserSettingsModel::adjustFrequencyForPulseWidth);
      connect(frequency,  &NTUserSetting::beforeValueChanged,   this,      &NTUserSettingsModel::adjustPulseWidthForFrequency);
    }
}

Is it correct way to give the path? How i have given inside my "QQmlComponent component". I think, it is not identifying the file in the path. How can i solve this issue? Thanks in advance.

[Maheshdev305]

@JennyAug13 said in Interfacing qml and c++:

QQmlComponent component(&engine, QUrl(QStringLiteral("Sources/QmlSources.qrc:/QML/Components/NTSpinBox.qml")));

try replacing this with

QQmlComponent component(&engine, QUrl(QStringLiteral(":/QML/Components/NTSpinBox.qml")));

[raven-worx]

@JennyAug13 said in Interfacing qml and c++:
Sources/QmlSources.qrc:/QML/Components/NTSpinBox.qml is not a valid url, thus the component never reaches the ready state.
did you mean qrc:/QML/Components/NTSpinBox.qml instead?

[J.Hilk]

I'm a bit confused here, does a QQmlEngine that is created as a local stack variable continue to exist after the end of the function scope?

[raven-worx]

@J.Hilk said in Interfacing qml and c++:

I'm a bit confused here, does a QQmlEngine that is created as a local stack variable continue to exist after the end of the function scope?

of course not. I haven't noticed this. :)
The mentioned error message is not related to this, but this would definitively be the next issue.

[J.Hilk]

@raven-worx
alright. I thought maybe some magic happens somewhere ;-)

this seems like a potential 3rd problem as well;
Creating a coponent, setting a property and than deleting it in more or less the same step. The compiler may even skip
the whole step during the optimization process.

QObject *object = component.create();
    object->setProperty("color","white");
    delete object;

[JennyAug13]

@raven-worx Yes it is ```
QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/QML/Components/NTIntensityControl.qml")));

[raven-worx]

@JennyAug13
anyway, like in your other post the biggest issue is:

QObject *object = component.create();
object->setProperty("color","white");
delete object;

[JennyAug13]

But the problem still exist, the problem is not with ```

QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:/QML/Components/NTIntensityControl.qml")));

but donot know, how can i change property in my qml file using c++ code and here is my qml file for your reference.

import QtQuick 2.3
import QtQuick.Layouts 1.1

import "../Theme"


Item {

    id: ntSpinBox

    objectName: "ntSpinBox"

    ///////////////////////////////////////////////////////////////////////////
    // Properties
    ///////////////////////////////////////////////////////////////////////////

    /// the currently selected value
    property var    value:   undefined // using var for generic list value support

    /// the minimum value of the range
    property double minimumValue: 0.0

    /// the maximum value of the range
    property double maximumValue: 10.0

    /// the stepSize for incrementing / decrementing values
    property double stepSize:     1.0

    /// a list / array of values to select from
    property var    itemList:     undefined

    /// Color of the buttons
    property color  color:        Theme.palette.button

    // speed of continuous update (press and hold) in stepSizes / sec
    property int continuousSpeed: Theme.settings.spinBoxSpeed

    /// determine if the value can be decremented further
    readonly property bool canDec: (itemList === undefined) ?
                                       (value > minimumValue) :
                                       (selectedIndex > 0)

    /// determine if the value can be incremented further
    readonly property bool canInc: (itemList === undefined) ?
                                       (value < maximumValue) :
                                       (selectedIndex < (itemList.length-1))

    /// if an itemList is set, this property holds the index of the currently
    /// selected item
    readonly property int selectedIndex: d.listIndex

    /// size of a button, internally used only
    readonly property real buttonSize: Math.min(ntSpinBox.width / 2,
                                                ntSpinBox.height)

    property bool greyout: false

    ///////////////////////////////////////////////////////////////////////////
    // Inherited Properties
    ///////////////////////////////////////////////////////////////////////////

    implicitWidth:  implicitHeight * 2 + Theme.diPaddingX
    implicitHeight: Theme.diControlHeight

    ///////////////////////////////////////////////////////////////////////////
    // Signals
    ///////////////////////////////////////////////////////////////////////////

    signal userSetVal();
    signal incBeyondMax(); ///< user tried to set a value > maximumValue

    ///////////////////////////////////////////////////////////////////////////
    // Slots
    ///////////////////////////////////////////////////////////////////////////

    Component.onCompleted: {
        d.updateListIndex();
    }

    onValueChanged: {
        d.updateListIndex();
    }

    ///////////////////////////////////////////////////////////////////////////
    // Private data
    ///////////////////////////////////////////////////////////////////////////

    QtObject
    {
        id: d

        property int  listIndex:    0
        property bool hasListItems: ntSpinBox.itemList !== undefined
        property real currentThreshold: ntSpinBox.maximumValue

        onListIndexChanged: {
            if (d.hasListItems) {
                ntSpinBox.value = ntSpinBox.itemList[d.listIndex];
            }
        }

        function updateListIndex() {
            if (!d.hasListItems) {
                return;
            }
            var newListIndex = itemList.indexOf(ntSpinBox.value);
            if (newListIndex !== d.listIndex && newListIndex !== -1) {
                d.listIndex = newListIndex;
            }
        }

        /// set new value if it is in specified range
        function setValue(newVal) {
            if (newVal <= ntSpinBox.maximumValue && newVal >= ntSpinBox.minimumValue) {
                ntSpinBox.value = newVal;
                userSetVal();
            }
        }

        function setListIndex(newIdx) {
            if (newIdx >= 0 && newIdx < itemList.length) {
                d.listIndex = newIdx;
            }
        }

        /// increment value by specified stepSize
        function inc() {
            var newVal = 0;
            if (d.hasListItems) {
                newVal = d.listIndex+1;
                setListIndex(newVal);
            }
            else {
                newVal = ntSpinBox.value + ntSpinBox.stepSize;
                setValue(newVal);
            }
            if(newVal > ntSpinBox.maximumValue) {
                incBeyondMax();
            }
        }

        /// decrement value by specified stepSize
        function dec() {
            if (d.hasListItems) {
                setListIndex(d.listIndex-1);
            }
            else {
                setValue(ntSpinBox.value - ntSpinBox.stepSize);
            }
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    // Child Components
    ///////////////////////////////////////////////////////////////////////////

    // Decrement Button
    NTActionButton {

        id: minusButton

        objectName: "minusButton"

        anchors.left: parent.left

        enabled: canDec
        greyout: ntSpinBox.greyout

        pressAndHoldEnable:   true
        pressAndHoldInterval: 1000 / continuousSpeed

        color:      ntSpinBox.color
        size:       ntSpinBox.buttonSize
        iconSource: itemList ? Theme.icons.back : Theme.icons.minus
        sound:      Theme.sounds.minusButtonSound

        onAction: {
            d.dec();
        }
    }

    // Increment Button
    NTActionButton {

        id: plusButton

        objectName: "plusButton"

        anchors.right: parent.right

        enabled: canInc
        greyout: ntSpinBox.greyout

        pressAndHoldEnable:   true
        pressAndHoldInterval: 1000 / continuousSpeed

        color:      ntSpinBox.color
        size:       ntSpinBox.buttonSize
        iconSource: itemList ? Theme.icons.next : Theme.icons.plus
        sound:      Theme.sounds.plusButtonSound

        onAction: {
            d.inc();
        }
    }
}