Add sample code showing how to create a new wxEvent class

In the event sample, show how create and use a new
wxEvent-derived class.

Closes https://github.com/wxWidgets/wxWidgets/pull/1633

samples/event/chessboard.h

@@ -0,0 +1,93 @@
+/////////////////////////////////////////////////////////////////////////////
+// Name:        samples/event/chessboard.h
+// Purpose:     Part of wxWidgets event sample, shows how to create a new wxEvent class
+// Author:      PB <pbfordev@gmail.com>
+// Created:     2019-10-29
+// Copyright:   (c) 2019 wxWidgets development team
+// Licence:     wxWindows licence
+/////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_CHESSBOARD_H_
+
+#include "wx/wx.h"
+
+// A chessboard consists of 8x8 squares organized
+// in columns (called files) and rows (called ranks).
+// In a 2D view, files are labeled from left to right
+// 'a' to 'h' while ranks are numbered from bottom to
+// top 1 to 8.
+// ChessBoardEvent tells us something happened on
+// the chessboard. Either a square was clicked
+// (myEVT_CHESSBOARD_CLICKED) or the mouse cursor was dragged
+// from one square to another (myEVT_CHESSBOARD_DRAGGED).
+class ChessBoardEvent : public wxCommandEvent
+{
+public:
+    ChessBoardEvent(wxEventType commandEventType = wxEVT_NULL, int id = 0)
+        : wxCommandEvent(commandEventType, id),
+          m_file('a'), m_rank(1), m_fileTo('a'), m_rankTo(1)
+    {}
+
+    // myEVT_CHESSBOARD_CLICKED: Returns File/Rank for the square clicked.
+    // myEVT_CHESSBOARD_DRAGGED: Returns File/Rank for the square
+    //                           the mouse cursor was dragged from.
+    char GetFile() const    { return m_file; }
+    wxUint8 GetRank() const { return m_rank; }
+
+    // Valid only for myEVT_CHESSBOARD_DRAGGED,
+    // returns File/Rank for the square where the mouse cursor was dragged to.
+    char GetFileTo() const    { return m_fileTo; }
+    wxUint8 GetRankTo() const { return m_rankTo; }
+
+    void SetFile(char file)    { m_file = file; }
+    void SetRank(wxUint8 rank) { m_rank = rank; }
+
+    void SetFileTo(char file)    { m_fileTo = file; }
+    void SetRankTo(wxUint8 rank) { m_rankTo = rank; }
+
+    virtual wxEvent* Clone() const wxOVERRIDE { return new ChessBoardEvent(*this); }
+private:
+    char  m_file;
+    wxUint8 m_rank;
+    char m_fileTo;
+    wxUint8 m_rankTo;
+};
+
+
+// Declare new event types,
+// the matching definitions are in chessboard.cpp.
+wxDECLARE_EVENT(myEVT_CHESSBOARD_CLICKED, ChessBoardEvent);
+wxDECLARE_EVENT(myEVT_CHESSBOARD_DRAGGED, ChessBoardEvent);
+
+// The following typedef and macro are needed only when the new event
+// class is to be used with event table macros or the legacy Connect(),
+// to cast the type of a function handling it to the type expected by
+// the event table machinery, see its use in EVT_CHESSBOARD_xxx below.
+// I.e., when only Bind() is going to be used you do not need them.
+typedef void (wxEvtHandler::*ChessBoardEventFunction)(ChessBoardEvent&);
+#define ChessBoardEventHandler(func) wxEVENT_HANDLER_CAST(ChessBoardEventFunction, func)
+
+// These defines are needed only if the new event is to be used with
+// event tables, i.e., when only Bind() is going to be used you do not need them.
+#define EVT_CHESSBOARD_CLICKED(id, func) \
+    wx__DECLARE_EVT1(myEVT_CHESSBOARD_CLICKED, id, ChessBoardEventHandler(func))
+#define EVT_CHESSBOARD_DRAGGED(id, func) \
+    wx__DECLARE_EVT1(myEVT_CHESSBOARD_DRAGGED, id, ChessBoardEventHandler(func))
+
+
+// Dialog displaying the chessboard
+// and handling ChessBoardEvents
+class MyChessBoardDialog : public wxDialog
+{
+public:
+    MyChessBoardDialog(wxWindow* parent);
+private:
+    void OnChessBoardClicked(ChessBoardEvent& event);
+    void OnChessBoardDragged(ChessBoardEvent& event);
+
+    // Just for demonstration, we will use an event table
+    // for myEVT_CHESSBOARD_CLICKED.
+    wxDECLARE_EVENT_TABLE();
+};
+
+#endif // #ifndef _WX_CHESSBOARD_H_