Subclassed Button Control
//=============================================================================
//SUBCLASSED CONTROLS: BUTTON - Copyright © 2000,2006 Ken Fitlike
//=============================================================================
//API functions used: CallWindowProc,CreateWindowEx,DefWindowProc,
//DestroyWindow,DispatchMessage,GetClientRect,GetDC,GetMessage,
//GetSystemMetrics,GetTextExtentPoint32,GetWindowLongPtr,GetWindowText,
//InvalidateRect,LoadImage,MessageBox,PostQuitMessage,RegisterClassEx,
//ReleaseDC,SendMessage,SetFocus,SetWindowLongPtr,SetWindowText,ShowWindow,
//UpdateWindow,TranslateMessage,WinMain.
//=============================================================================
//Demonstrates subclassing of button control. This uses the traditional
//approach to window subclassing by employing the SetWindowLongPtr api 
//function to change the default, system window procedure to the user-defined
//one. This technique can be used with win9x and later operating systems.
//=============================================================================
#include <windows.h>  //include all the basics
#include <tchar.h>    //string and other mapping macros
#include <string>
#include <vector>

//define an unicode string type alias
typedef std::basic_string<TCHAR> ustring;
//=============================================================================
//main window message handling function declarations
LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
int OnCreate(const HWND,CREATESTRUCT*);

//subclassed button message handling function declarations
LRESULT CALLBACK BtnProc(HWND,UINT,WPARAM,LPARAM);
HWND OnRightClick(const HWND);
void OnMouseClick(const HWND,const HWND);

HWND CreateControl(const HWND,const HINSTANCE,DWORD,const RECT&,const int,
                   const ustring&,const ustring& classname);
inline int ErrMsg(const ustring&);

//setup control id's
enum {
  IDC_BUTTON=200,
  IDC_EDIT
};
//=============================================================================
int WINAPI WinMain(HINSTANCE hInst,HINSTANCE,LPSTR pStr,int nCmd)
{
ustring classname=_T("SIMPLEWND");
WNDCLASSEX wcx={0};  //used for storing information about the wnd 'class'

wcx.cbSize         = sizeof(WNDCLASSEX);           
wcx.lpfnWndProc    = WndProc;             //wnd Procedure pointer
wcx.hInstance      = hInst;               //app instance
//use 'LoadImage' to load wnd class icon and cursor as it supersedes the 
//obsolete functions 'LoadIcon' and 'LoadCursor', although these functions will 
//still work. Because the icon and cursor are loaded from system resources ie 
//they are shared, it is not necessary to free the image resources with either 
//'DestroyIcon' or 'DestroyCursor'.
wcx.hIcon         = reinterpret_cast<HICON>(LoadImage(0,IDI_APPLICATION,
                                            IMAGE_ICON,0,0,LR_SHARED));
wcx.hCursor       = reinterpret_cast<HCURSOR>(LoadImage(0,IDC_ARROW,
                                              IMAGE_CURSOR,0,0,LR_SHARED));
wcx.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_BTNFACE+1);   
wcx.lpszClassName = classname.c_str(); 
//the window 'class' (not c++ class) has to be registered with the system
//before windows of that 'class' can be created
if (!RegisterClassEx(&wcx))
  {
  ErrMsg(_T("Failed to register wnd class"));
  return -1;
  }

int desktopwidth=GetSystemMetrics(SM_CXSCREEN);
int desktopheight=GetSystemMetrics(SM_CYSCREEN);

HWND hwnd=CreateWindowEx(0,                     //extended styles
                         classname.c_str(),     //name: wnd 'class'
                         _T("Subclassed Button Control"), //wnd title
                         WS_OVERLAPPEDWINDOW,   //wnd style
                         desktopwidth/4,        //position:left
                         desktopheight/4,       //position: top
                         desktopwidth/2,        //width
                         desktopheight/2,       //height
                         0,                     //parent wnd handle
                         0,                     //menu handle/wnd id
                         hInst,                 //app instance
                         0);                    //user defined info
if (!hwnd)
  {
  ErrMsg(_T("Failed to create wnd"));
  return -1;
  }

ShowWindow(hwnd,nCmd); 
UpdateWindow(hwnd);
//start message loop - windows applications are 'event driven' waiting on user,
//application or system signals to determine what action, if any, to take. Note 
//that an error may cause GetMessage to return a negative value so, ideally,  
//this result should be tested for and appropriate action taken to deal with 
//it(the approach taken here is to simply quit the application).
MSG msg;
while (GetMessage(&msg,0,0,0)>0)
  {
  TranslateMessage(&msg);
  DispatchMessage(&msg);
  }
return static_cast<int>(msg.wParam);
}
//=============================================================================
LRESULT CALLBACK WndProc(HWND hwnd,UINT uMsg,WPARAM wParam,LPARAM lParam)
{
switch (uMsg)
  {
  case WM_CREATE:
    return OnCreate(hwnd,reinterpret_cast<CREATESTRUCT*>(lParam));
  case WM_DESTROY:
    PostQuitMessage(0);    //signal end of application
    return 0;
  default:
    //let system deal with msg
    return DefWindowProc(hwnd,uMsg,wParam,lParam);  
  }
}
//=============================================================================
int OnCreate(const HWND hwnd,CREATESTRUCT *cs)
{
//handles the WM_CREATE message of the main, parent window; return -1 to fail
//window creation
RECT rc={10,10,260,40};
//the various button types are created by simply varying the style bits
HWND hBtn=CreateControl(hwnd,cs->hInstance,BS_DEFPUSHBUTTON,rc,IDC_BUTTON,
                        _T("Right-click to edit this caption"),_T("button"));

//subclass the button control
WNDPROC OldBtnProc=reinterpret_cast<WNDPROC>(static_cast<LONG_PTR>(
             SetWindowLongPtr(hBtn,GWLP_WNDPROC,
             reinterpret_cast<LONG_PTR>(BtnProc)))); 
             
//store the original, default window procedure of the button as the button
//control's user data
SetWindowLongPtr(hBtn,GWLP_USERDATA,reinterpret_cast<LONG_PTR>(OldBtnProc));

SetFocus(hBtn);                 
return 0;
}
//=============================================================================
HWND CreateControl(const HWND hParent,const HINSTANCE hInst,DWORD dwStyle,
                   const RECT& rc,const int id,const ustring& caption,
                   const ustring& classname)
{
dwStyle|=WS_CHILD|WS_VISIBLE;
return CreateWindowEx(0,                            //extended styles
                      classname.c_str(),            //control 'class' name
                      caption.c_str(),              //control caption
                      dwStyle,                      //control style 
                      rc.left,                      //position: left
                      rc.top,                       //position: top
                      rc.right,                     //width
                      rc.bottom,                    //height
                      hParent,                      //parent window handle
                      //control's ID
                      reinterpret_cast<HMENU>(static_cast<INT_PTR>(id)),
                      hInst,                        //application instance
                      0);                           //user defined info
}
//=============================================================================
inline int ErrMsg(const ustring& s)
{
return MessageBox(0,s.c_str(),_T("ERROR"),MB_OK|MB_ICONEXCLAMATION);
}
//=============================================================================
//subclassed button window procedure and message handling functions
//=============================================================================
LRESULT CALLBACK BtnProc(HWND hwnd,UINT uMsg,WPARAM wParam,LPARAM lParam)
{
//This is the subclass window procedure for the button. If the mouse is 
//right-clicked on the button then a single line, flat edit control is created 
//and the button caption copied into it. Any other mouse message (except 
//movement) on the button results in the edit's text being copied as the button 
//caption. The edit control is then destroyed.
static HWND hEdit;
//retrieve the previously stored original button window procedure 
static WNDPROC OrigBtnProc=reinterpret_cast<WNDPROC>(static_cast<LONG_PTR>(
                           GetWindowLongPtr(hwnd,GWLP_USERDATA)));
switch (uMsg)
  {
  //if any of the following mouse events occur, check if the edit control 
  //exists. If it does then copy its text to the button caption before 
  //destroying the edit control.
  case WM_LBUTTONDOWN:
  case WM_MBUTTONDOWN:
  case WM_LBUTTONDBLCLK:
  case WM_MBUTTONDBLCLK:
  case WM_RBUTTONDBLCLK:
    {
    OnMouseClick(hwnd,hEdit);
    //ensure default message handling occurs
    return CallWindowProc(OrigBtnProc,hwnd,uMsg,wParam,lParam);
    }
  //mouse button right-click event
  case WM_RBUTTONDOWN:
    {
    if (!IsWindow(hEdit))
      {
      hEdit=OnRightClick(hwnd);
      }
    return 0;
    }
  default:
    //call the default system handler for the control (button)
    return CallWindowProc(OrigBtnProc,hwnd,uMsg,wParam,lParam);
  }
}
//=============================================================================
void OnMouseClick(const HWND hwnd,const HWND hEdit)
{
//event handler for all mouse click messages except WM_RBUTTONDOWN 
//(right-click)
//check if the edit control exists. If it does then copy its text to the button 
//caption before destroying the edit control.

if (IsWindow(hEdit))
  {
  const int MAX_TXT_LEN=64;
  //get the edit text
  std::vector<TCHAR> tmp(MAX_TXT_LEN);
  tmp.push_back(_T('\0'));
  
  if (GetWindowText(hEdit,&tmp[0],MAX_TXT_LEN))
    {
    SetWindowText(hwnd,&tmp[0]);
    }
  DestroyWindow(hEdit);
  InvalidateRect(hwnd,0,1);    //ensure button is completely redrawn
  }
}
//=============================================================================
HWND OnRightClick(const HWND hwnd)
{
//mouse button right-click event handler. Return handle of the edit control
//get the button text and its dimensions
const int MAX_TXT_LEN=64;
std::vector<TCHAR> tmp(MAX_TXT_LEN);
tmp.push_back(_T('\0'));
        
int t=GetWindowText(hwnd,&tmp[0],MAX_TXT_LEN);
        
SIZE sz={0};
HDC hdc=GetDC(hwnd);
GetTextExtentPoint32(hdc,&tmp[0],t+1,&sz);
ReleaseDC(hwnd,hdc);
        
//to ensure edit control is created with a usable minimum width
//get width of eg. 4 characters.
int nMin=(sz.cx/(static_cast<int>(tmp.size())))*4;
if (sz.cx<nMin)
  {
  sz.cx=nMin;
  }
sz.cy+=4;    //ensure a decent border around edit control's text
//get button dimensions and adjust those values based on text 
//dimensions to calculate edit control's dimensions.
RECT  rc={0};
GetClientRect(hwnd,&rc);
rc.top=(rc.bottom-sz.cy)/2;
        
rc.left=(rc.right-sz.cx)/2;
rc.right=sz.cx;
rc.bottom=sz.cy;
//create a flat, single line edit control and ensure its width has a 
//reasonable minimum value.
HINSTANCE hInst=reinterpret_cast<HINSTANCE>(static_cast<LONG_PTR>(
                  GetWindowLongPtr(hwnd,GWLP_HINSTANCE)));
HWND hEdit=CreateControl(hwnd,hInst,WS_BORDER|ES_AUTOHSCROLL,rc,IDC_EDIT,
                         &tmp[0],_T("edit"));                        
//highlight the text and set focus on the edit control 
SendMessage(hEdit,EM_SETSEL,0,static_cast<LPARAM>(-1));
SetFocus(hEdit);
return hEdit;
}
//=============================================================================