How to make the SplineSeries's appended values permanent?

ugurkebir

I created an item called Chart. I put chartview and splineseries in it. Then I created Chart modules in another item and appended the chart values. But on page transition old splineseries values are lost and regenerated. That's why I can't see the old values in the chart. How can I make the SplineSeries's appended values permanent?

Chart.qml:

import QtQuick 2.12
import QtCharts 2.3
import "Global"

Item {
    id: chartComponent

    property double xVal: 0.0
    property double yVal: 0.0

    Rectangle{
        id: temperatureChartRect
        //...

        Rectangle{
            id: temperatureChartHeader
            //...
            Text {
                id: temperatureChartHeaderTxt
                //...
            }
        }

        ChartView {
            id: temperatureChart
            //...
            clip: true
            antialiasing: true
            backgroundRoundness: 0.0
            legend.visible: false

            Rectangle{
                id: rectang
                //...
            }

            ValueAxis {
                id: valueAxisY
                min: yVal < 0 ? Math.min(yVal*1.2, 0) : yVal*0.5
                max: Math.max(yVal*1.2, yVal)
                tickCount: Math.min(temperatureChart.height/40, 25)
            }
            ValueAxis {
                id: valueAxisX
                min: 0
                max: Math.max(xVal*1.2, xVal)
                tickCount: Math.min(temperatureChart.width/40, temperatureChartSeries.count)
            }

            SplineSeries {
                id: temperatureChartSeries
                axisX: valueAxisX
                axisY: valueAxisY
                useOpenGL: true
            }
        }
    }

    onXValChanged : {
        temperatureChartSeries.append(xVal, yVal)
        console.log("SplineSeries count : ", temperatureChartSeries.count)
    }
}

someOther.qml (Callee qml):

import QtQuick 2.12
import QtQuick.Layouts 1.12
import QtQuick.Controls 2.15
import QtCharts 2.3
import "Global"

Item {
    id: remoteControlPage
    FontLoader { id: fontFamily; source: Style.fontFamilySource }

    //...
    //...

    property int timerCountQml: serialCommQml.timerCount
    property var sensorChartQml: serialCommQml.command.sensorChart

    Chart {        //Chart1
        id: pt100TempChart
        anchors.top: parent.top
        anchors.left: stateStatus.right
        anchors.leftMargin: 20
        width: Math.max(300, parent.width / 3)
        height: Math.max(250, parent.height/3)
        chartName: "PT100 Temperature"

        xVal:timerCountQml
        yVal: sensorChartQml.pt100Temp
    }

    Chart {        //Chart2
        //...
    }

    Chart {        //Chart3
        //...
    }

    Chart {        //Chart4
        //...
    }
}

Application Output:
qml: SplineSeries count : 1 //Chart1
qml: SplineSeries count : 1 //Chart2
qml: SplineSeries count : 1 //Chart3
qml: SplineSeries count : 1 //Chart4
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
//...
//...
qml: SplineSeries count : 25
qml: SplineSeries count : 25
qml: SplineSeries count : 25
qml: SplineSeries count : 25
qml: GmtNavigationButton_QMLTYPE_7(0x55e0c0dc9d80) //page transition
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
//...
//...
qml: GmtNavigationButton_QMLTYPE_7(0x55e0c0dc9d80) //page transition
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 1
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
qml: SplineSeries count : 2
//...
//...

Screenshots:
26 seconds of graphic display before page transition

After 26 seconds the page transition took place and the data started to regenerate in 26 seconds. But the first 26 seconds of data was lost.