How to save current index of ComboBox for supported map types - qt

Question

I try to save index of ComboBox for choosing supported map types of Open Street Map. When opening the app again, the last chosen map index should be displayed. Qt.labs.settings didn't work as the example below:
import QtQuick 2.6
import QtQuick.Controls 2.0
import QtLocation 5.12
import QtPositioning 5.12
import Qt.labs.settings 1.0
ApplicationWindow{
id: root
width: 500
height: 500
visible: true
Settings{
id:mycombo
property alias maptype: selectmap.currentIndex
}
Flickable {
height: parent.height
width: parent.width
clip: true
contentHeight: Math.max(mapColumn.implicitHeight, height)
Column{
anchors.horizontalCenter: parent.horizontalCenter
id:mapColumn
spacing: 5
anchors.fill : parent
Row{
anchors.horizontalCenter: parent.horizontalCenter
spacing:25
Rectangle{
width:mapColumn.width
height:mapColumn.height-80
Map {
id:map
anchors.fill: parent
plugin: Plugin {
name: "osm"
}
}
}
}
Column{
id: combos
spacing: 10
width: parent.width
anchors.verticalCenter: root.verticalCenter
Row{
anchors.horizontalCenter: parent.horizontalCenter
spacing:1
Label{ text:"Map Type: "; height: selectmap.height; verticalAlignment: Text.AlignVCenter; }
// Map Types
ComboBox {
id: selectmap
width: 200
model:map.supportedMapTypes
textRole:"description"
onCurrentIndexChanged: map.activeMapType = map.supportedMapTypes[currentIndex]
}
}
}
}
}
}
Is it possible to save the current index of ComboBox for maps?

Answer 1

By saying "opening the app again" it is possible that the app has been killed, and in that case all values are lost. You have to store the index value in the file system, like config data, which is read when application loads. I guess there will be several of these data, including last typed places and history(for which cache is better). However for config data you may use JSON format.
Make a JSON file where you store all data, and make a controller like GuiConfigurationController which parses the file with QJsonValue. You may also consider to make a GuiConfiguration Singletonn class which will have all the values loaded as getter method. To write to the JSON file from QML use the Q_PROPERTY WRITE method which calls the setter method for the variable.
Q_PROPERTY(quint32 savedIndex READ savedIndex WRITE setSavedIndex NOTIFY savedIndexChanged)
quint32 savedIndex() const {return m_savedIndex;}
void setSavedIndex(quint32 index) {m_savedIndex = index;}
QML:
_someController.savedIndex = currentIndex
make sure _someController is set as rootContext -> ContextProperty to QQuickView
so when index changes the value is set in someController which saved the value to JSON. When app is loading read JSON and get the value of index. Update QtQuick using the onLoaded method
onLoaded: {currentindex = _someController.savedIndex}