Save the setting of plugins

Save the setting of plugins
Now I'm improving the shakuhachi, koto and shinobue notation plugins.
I‘d like to save the setting of plugins.
Prototype code is

import QtQuick 2.2
import MuseScore 1.0
import FileIO 1.0
import QtQuick.Controls 1.0
import QtQuick.Dialogs 1.0
import QtQuick.Layouts 1.1

MuseScore {
  menuPath: "Plugins.writeReadSeettingsDemo"
  version: "2.0"
  description: qsTr("This plugin Write and Read the setting of plugin")
  pluginType: "dialog"

  id: window
  width:200
  height:100
  ExclusiveGroup { id: exclusiveGroupKey }

  RowLayout {
    id: column
    x : 10
    y : 10
    Label {
      font.pointSize: 14
      text: "Select" 
    }
  }


  RowLayout {
    x : 60
    y : 10
  ComboBox {

 //   currentIndex: Number(fileContents[0])     //      doesn't work
    currentIndex: comboBoxInitValue     //      doesn't work

    model: ListModel {
      id: chooseList
      property var key

      ListElement { text: "choose A"; fName: 1 }
      ListElement { text: "choose B"; fName: 2 }
      ListElement { text: "choose C"; fName: 3 }
    }
    width: 100
    onCurrentIndexChanged: {
      console.debug(chooseList.get(currentIndex).text + ", " +chooseList.get(currentIndex).fName)
      chooseList.key = chooseList.get(currentIndex).fName
      console.debug(chooseList.key)
    }
  } // end ComboBox
  }

  RowLayout {
    x : 50
    y : 60
    Button {
      id: closeButton
      text: "Close"
      onClicked: { Qt.quit() }
    }
    Button {
      id: okButton
      text: "Ok"
      onClicked: {
        apply()
        Qt.quit()
      }
    }
  }


  function apply() {
    curScore.startCmd()
    my_file1.write(chooseList.key);
    curScore.endCmd()           
  }


  onRun: {
    var fileContents = my_file1.read();
    console.log("Read from file value="+ Number(fileContents[0]));
    var comboBoxInitValue =Number(fileContents[0])                      //    <<

    if (typeof curScore === 'undefined')   Qt.quit();
  }


  FileIO {
    id: my_file1

    source: tempPath() + "/temp9999.txt"           //  <<<

    onError: console.log(msg)
  }
}

Q1.
The stored value could be read, but couldn't use at the next run.
Line 35 or 36 doesn’t work.
35: // currentIndex: Number(fileContents[0]) // doesn't work
36: currentIndex: comboBoxInitValue // doesn't work

Is there method to set "currentIndex:” from variable?

Q2.
Line 93
93:  source: tempPath() + "/temp9999.txt"
Where is the tempPath()? 
I couldn’t find temp9999.txt file.
If possible, I want to save as a permanent file,
like ./temp9999.txt

Please advise me.