DlgProc

In a plugin there must be a dialog callback function, which is responsible for processing events and messages sent to the dialog. The function has four parameters: dialog handle, message and two additional parameters.

Dialog handler function syntax is presented here, as it should appear in a plugin.

Parameters

hDlg

Dialog handle

Msg

One of events or messages.

Param1

Parameter 1

Param2

Parameter 2

Return value

The DlgProc function return value depends on the Msg parameter.

Remarks

Sometimes information contained in Param1 and Param2 consists of two parts, which are placed in two 16-bit words, composing each parameter. There're two macros defined in Windows to provide access to each part of Param1 and Param2 - LOWORD and HIWORD.
They return high-order and low-order words respectively from long int 32-bit value.

Example

Dialog handler code fragment for Reversi game:

LONG_PTR WINAPI ReversiDialogProc(HANDLE hDlg, int Msg,int Param1,LONG_PTR Param2)
{
  struct FarDialogItem DialogItem;
  struct FarListItem *ListItems;
  int i;

  switch(Msg)
  {
    case DN_INITDIALOG:
      // Get information about the element
      Info.SendDlgMessage(hDlg,DM_GETDLGITEM,75,(LONG_PTR)&DialogItem);
      ListItems=DialogItem.ListItems->Items;
      ...
      NewGame(hDlg);
      return FALSE;

    case DN_HELP:
    {
      // Show different help topics depending on game move
      static char *Help[3]={"Contents","Rule","Recommendations"};
      if(NumPl1==2 && NumPl2 == 2)
        i=0;
      else if(NumPl1+NumPl2 > 16)
        i=2;
      else
        i=1;
      return (LONG_PTR)(Help[i]);
    }
    ...

    case DM_CLOSE:
      // Check the element with which the user tries to close the dialog
      if(Param1 != 10 && Param1 > 0)
        return FALSE;  // one can't close the dialog
      break;
  }

  // Let the Dialog Manager process other events and messages
  return Info.DefDlgProc(hDlg,Msg,Param1,Param2);
}