any code out there with/including dropdown list/combobox button?

[joshatt]

Recently I'm excited to find some youtube tutorials about onchartevent and button and dialog,etc. in official library. I successfully wrote a code with button, as well as with button in a dialog.  But then when I tried to code a dropdown list (not in input and ENUM..., I want the button in chart), I don't know which but I think combobox is what I have to use, and the following code does not work as wish, there's no default value, and whatever I chose it kept empty.  Is there any example code out there I could learn from? Or detailed documentation about everything in official library?

#property strict
#property indicator_chart_window
#include <Controls\ComboBox.mqh>
CComboBox box;

int OnInit()
  {
   ChartSetInteger(0,CHART_EVENT_MOUSE_MOVE,true);

   box.Create(0,"box1",0,250,0,380,30);
   box.ItemAdd("5min");
   box.ItemAdd("15min");
   box.ItemAdd("30min");

   return(INIT_SUCCEEDED);
  }

void OnDeinit(const int reason)
  {
   box.Destroy(reason);
  }

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
  {
   return(rates_total);
  }

void OnChartEvent(const int id,
                  const long &lparam,
                  const double &dparam,
                  const string &sparam)
  {
   box.OnEvent(id,lparam,dparam,sparam);
  }