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C++ Backend Charts Demo App

 import QtQuick 2.0
 import QtCharts 2.2

 Item {
   anchors.fill: parent

   ChartView {
     id: chartView
     width: parent.width
     height: parent.height * 0.5

     BarSeries {
       id: mySeries

       axisX: BarCategoryAxis {
         categories: {
           var arr = []
           var used = {}
           for(var i = 0; i < chartData.length; i++) {
             var year = chartData[i].year
             if(!used[year]) {
               arr.push(year)
               used[year] = true
             }
           }
           return arr
         }
       }
       axisY: ValueAxis {
         min: 0
         max: 50000
       }

       Connections {
         target: app
         onChartDataChanged: mySeries.udpateBarSeries()
       }
       Component.onCompleted: mySeries.udpateBarSeries()

       function udpateBarSeries() {
         mySeries.clear()
         var expenses = {}
         var maxExpense = 0
         for(var i = 0; i < chartData.length; i++) {
           var model = chartData[i]
           if(expenses[model.city] === undefined)
             expenses[model.city] = []

           expenses[model.city].push(parseInt(model.expenses))
           if(model.expenses > maxExpense)
             maxExpense = model.expenses
         }

         mySeries.axisY.max = maxExpense
         for(var city in expenses) {
           mySeries.append(city, expenses[city])
         }
       }