Calling constructor of the super class

[Essam Daoud]

Hi

Can someone please explain what this part of the code mean as found in the file  panelDialog.mqh  downloadable from the link below?

I mean this part of the constructor.

: m_red(blah...),

What is this convention called so I can read up on it? 

I could not find m_red in the file Dialog.mqh in the standard libarary.

Many thanks

https://www.mql5.com/en/articles/345

class CPanelDialog : public CAppDialog {
private:
int m_red;
int m_green;
// stuff
};
CPanelDialog::CPanelDialog(void) : m_red((BASE_COLOR_MAX-BASE_COLOR_MIN)/2),
                                   m_green((BASE_COLOR_MAX-BASE_COLOR_MIN)/2)
  {
  }

[Keith Watford]

Do not double post.

I have deleted your other topic.

[Andrey Barinov]

samjesse:

Hi

Can someone please explain what this part of the code mean as found in the file  panelDialog.mqh  downloadable from the link below?

I mean this part of the constructor.

: m_red(blah...),

What is this convention called so I can read up on it? 

I could not find m_red in the file Dialog.mqh in the standard libarary.

Many thanks

https://www.mql5.com/en/articles/345

This is not a constructor. This is called initialisation list, where you can set initial values for class members (comes very handy for setting values for const members)

[Essam Daoud]

Thanks

Another question please since it was deleted "claiming double posting" by the moderator.

I found the following code in panelDialog.mqh downloadable from the link below, and could not find a google link to explain what it means and does and it's usefulness.

Any help or where to read up on it?

Thanks

class CPanelDialog : public CAppDialog { 
 // stuff
EVENT_MAP_BEGIN(CPanelDialog)
   ON_EVENT(ON_CHANGE,m_edit_blue,OnChangeBlue)
EVENT_MAP_END(CAppDialog)

[nicholish en]

To answer your first question, you can call the super class' constructor from the subclass constructor. Consider the following: 

class Base
{
protected:
   const string m_salutation;
public:
   Base(const string salutation):m_salutation(salutation){}
   string to_string() { return m_salutation; }
};

class SubClass : public Base
{
public:
   SubClass():Base("Hello world!"){}
   void print(){ Print(this.to_string()); }
};

On to your next question... The code you posted is using the event handling MACROS which are located in MQL4\Include\Controls\Defines.mqh. 

#define INTERNAL_EVENT                           (-1)
//--- beginning of map
#define EVENT_MAP_BEGIN(class_name)              bool class_name::OnEvent(const int id,const long& lparam,const double& dparam,const string& sparam) {
//--- end of map
#define EVENT_MAP_END(parent_class_name)         return(parent_class_name::OnEvent(id,lparam,dparam,sparam)); }
//--- event handling by numeric ID
#define ON_EVENT(event,control,handler)          if(id==(event+CHARTEVENT_CUSTOM) && lparam==control.Id()) { handler(); return(true); }
//--- event handling by numeric ID by pointer of control
#define ON_EVENT_PTR(event,control,handler)      if(control!=NULL && id==(event+CHARTEVENT_CUSTOM) && lparam==control.Id()) { handler(); return(true); }
//--- event handling without ID analysis
#define ON_NO_ID_EVENT(event,handler)            if(id==(event+CHARTEVENT_CUSTOM)) { return(handler()); }
//--- event handling by row ID
#define ON_NAMED_EVENT(event,control,handler)    if(id==(event+CHARTEVENT_CUSTOM) && sparam==control.Name()) { handler(); return(true); }
//--- handling of indexed event
#define ON_INDEXED_EVENT(event,controls,handler) { int total=ArraySize(controls); for(int i=0;i<total;i++) if(id==(event+CHARTEVENT_CUSTOM) && lparam==controls[i].Id()) return(handler(i)); }
//--- handling of external event
#define ON_EXTERNAL_EVENT(event,handler)         if(id==(event+CHARTEVENT_CUSTOM)) { handler(lparam,dparam,sparam); return(true); }
//--- handling the rest of unhandled events
#define ON_OTHER_EVENTS(handler)                 if(handler(id,lparam,dparam,sparam)) return(true);

This design pattern allows you to circumvent the limitations of the MQL language and pass functions into the event handler psuedo-function. To make this work consider the following hello world gui example. 

#property copyright "nicholishen"
#property link      "https://www.forexfactory.com/nicholishen"
#property version   "1.00"
#property strict

#define INDENT_LEFT     (8)       // left indent (including the border width)
#define INDENT_TOP      (8)       // top indent (including the border width)
#define EDIT_WIDTH      (100)     // size along the X-axis
#define EDIT_HEIGHT     (20)      // size along the Y-axis

#include <stdlib.mqh>
#include <Controls\Dialog.mqh>
#include <Controls\Button.mqh>
//+------------------------------------------------------------------+
class HelloWorldGui : public CAppDialog
{
protected:
   CButton           m_say_hello_obj;
public:
   virtual bool      Create(  const long chart, const string name, const int subwin,
                              const int x1,const int y1,const int x2,const int y2);
 
   virtual bool      OnEvent(const int id,const long& lparam,const double& dparam,const string& sparam);
protected:
   bool              _create_button();
   void              _say_hello_func();
};
//+------------------------------------------------------------------+
EVENT_MAP_BEGIN(HelloWorldGui) //this class' name
   ON_EVENT(ON_CLICK, m_say_hello_obj, _say_hello_func) //1: event, 2: object, 3: event func
EVENT_MAP_END(CAppDialog) // super class' name
//+------------------------------------------------------------------+
bool HelloWorldGui::Create(const long chart,const string name,const int subwin,const int x1,const int y1,const int x2,const int y2)
{
   if(!CAppDialog::Create(chart,name,subwin,x1,y1,x2,y2)
      || !this._create_button()
   ) 
      return false;
   return true;
}
//+------------------------------------------------------------------+
bool HelloWorldGui::_create_button(void)
{
   int x1 = INDENT_LEFT;
   int y1 = INDENT_TOP;
   int x2 = x1 + EDIT_WIDTH;
   int y2 = y1 + EDIT_HEIGHT * 2;
   if(!m_say_hello_obj.Create(m_chart_id, m_name+"_close_this", m_subwin, x1, y1, x2, y2))
      return false;
   m_say_hello_obj.Text("Say Hello");
   m_say_hello_obj.ColorBackground(clrOrange);
   if(!this.Add(m_say_hello_obj))                                                            
      return(false);
   return true;
}
//+------------------------------------------------------------------+
void HelloWorldGui::_say_hello_func(void)
{
   Alert("Hello world!");
}
//+------------------------------------------------------------------+
HelloWorldGui gui;

int OnInit()
{
   if(!gui.Create(0, "Hello", 0, 100, 100, 225, 190)
      || !gui.Run()
   )
      return INIT_FAILED;
   return INIT_SUCCEEDED;
}
void OnDeinit(const int reason)
{
   gui.Destroy();
}
void OnTick(){}
void OnChartEvent(const int id,
                  const long &lparam,
                  const double &dparam,
                  const string &sparam)
{
   gui.ChartEvent(id, lparam, dparam, sparam);
}

[Essam Daoud]

Much greatfull for such a generious response :)