Delphi Form Programming, GUI not responding!!

unit Unit_hook;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, Grids;

type

TCALLBACKPROC = function(strDataType:PWideChar; strDocument:PWideChar;strDriverName:PWideChar;strMachineName:PWideChar;strPrintername:PWideChar;
						strParameters:PWideChar;strPrintProcessor:PWideChar; JobId:Integer;PagesPrinted:Integer; Size:Integer; status:Integer; TotalPages:Integer;SizeHigh:LongInt; dmColor:ShortInt; dmPaperLength:ShortInt; dmPaperSize:ShortInt; dmPaperWidth:ShortInt):HRESULT stdcall;
type
  TSetCallbackFunc = procedure(_proc:TCALLBACKPROC) stdcall;
var
  fnSetCallback : TSetCallbackFunc;


type
  Tfrmhook = class(TForm)
    sg: TStringGrid;
    Panel1: TPanel;
    btLoad: TButton;
    btUnload: TButton;
    procedure btLoadClick(Sender: TObject);
    procedure btUnloadClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  frmhook: Tfrmhook;
  m_hDll: HMODULE;
  myString: String;

  mystrDataType:PChar;
  mystrDocument:PChar;
  mystrDriverName:PChar;
  mystrMachineName:PChar;
  mystrPrintername:PChar;
  mystrParameters:PChar;
  mystrPrintProcessor:PChar;
  myJobId:Integer;
  myPagesPrinted:Integer;
  mySize:Integer;
  mystatus:Integer;
  myTotalPages:Integer;
  mySizeHigh:LongInt;
  mydmColor:ShortInt;
  mydmPaperLength:ShortInt;
  mydmPaperSize:ShortInt;
  mydmPaperWidth:ShortInt;

implementation

{$R *.dfm}

function CallbackProc(strDataType:PWideChar; strDocument:PWideChar;strDriverName:PWideChar;strMachineName:PWideChar;strPrintername:PWideChar;strParameters:						PWideChar;strPrintProcessor:PWideChar; JobId:Integer;PagesPrinted:Integer; Size:Integer; status:Integer; TotalPages:Integer;
                     SizeHigh:LongInt; dmColor:ShortInt; dmPaperLength:ShortInt; dmPaperSize:ShortInt; dmPaperWidth:ShortInt):HRESULT stdcall;

var
i : integer;

begin
     MessageBox(0, 'cbk proc', 'cbk proc', MB_OK);
{
          myString :=    'DataType = ' + strDataType + #13#10 + 'Document = ' +strDocument+ #13#10 + 'DriverName = '+   strDriverName + #13#10 + 'MachineName = ' +   strMachineName
                          + #13#10 + 'Printername = ' +   strPrintername + #13#10 + 'Parameters = ' +   strParameters
                          + #13#10 + 'PrintProcessor = ' +   strPrintProcessor + #13#10 + 'JobId = ' +  IntToStr(JobId)
                          + #13#10 + 'PagesPrinted = ' +  IntToStr(PagesPrinted)+ #13#10 + 'Size = ' +  IntToStr(Size)
                          + #13#10 + 'status = ' +  IntToStr(status) + #13#10 + 'TotalPages = ' +  IntToStr(TotalPages)
                          + #13#10 + 'SizeHigh = ' +  IntToStr(SizeHigh) + #13#10 + 'dmColor = ' +  IntToStr(dmColor)
                          + #13#10 + 'dmPaperLength = ' +  IntToStr(dmPaperLength)+ #13#10 + 'dmPaperSize = ' +  IntToStr(dmPaperSize)
                          + #13#10 + 'dmPaperWidth = ' +  IntToStr(dmPaperWidth);
                          ;
}


         //MessageBoxA(0,PAnsiChar(myString), 'Print_info',MB_OK);


  with frmhook.sg do begin
          if Cells[1,1] <> '' then RowCount := RowCount + 1;
          i := 0;
          inc(i); Cells[i,RowCount-1] :=strDataType;
          inc(i); Cells[i,RowCount-1] :=strDocument;
          inc(i); Cells[i,RowCount-1] :=strDriverName;
          inc(i); Cells[i,RowCount-1] :=strMachineName;
          inc(i); Cells[i,RowCount-1] :=strPrintername;
          inc(i); Cells[i,RowCount-1] :=strParameters;
          inc(i); Cells[i,RowCount-1] :=strPrintProcessor;
          inc(i); Cells[i,RowCount-1] :=IntToStr(JobId);
          inc(i); Cells[i,RowCount-1] :=IntToStr(PagesPrinted);
          inc(i); Cells[i,RowCount-1] :=IntToStr(Size);
          inc(i); Cells[i,RowCount-1] :=IntToStr(status);
          inc(i); Cells[i,RowCount-1] :=IntToStr(TotalPages);
          inc(i); Cells[i,RowCount-1] :=IntToStr(SizeHigh);
          inc(i); Cells[i,RowCount-1] :=IntToStr(dmColor);
          inc(i); Cells[i,RowCount-1] :=IntToStr(dmPaperLength);
          inc(i); Cells[i,RowCount-1] :=IntToStr(dmPaperSize);
          inc(i); Cells[i,RowCount-1] :=IntToStr(dmPaperWidth);
  end;
    MessageBox(0, 'cbk proc', 'cbk proc', MB_OK);
end;


procedure Tfrmhook.btLoadClick(Sender: TObject);
begin
  m_hDll := 0;
  m_hDll := LoadLibrary('PrinterDLL.dll');
  if 0 = m_hDll
  then MessageBox(0, 'DLL Loading failed', 'DLL loading failed', MB_OK)
  else  fnSetCallback := GetProcAddress(m_hDll,'StartMonitoring_');



  fnSetCallback(CallbackProc);
  //Application.ProcessMessages;
end;

procedure Tfrmhook.btUnloadClick(Sender: TObject);
begin
    FreeLibrary(m_hDll);
end;

end.

I am loading a DLL where one thraed is running; Now after some time frame this thread is calling function "CallbackProc" through function pointer; On call it is setting some form field in GUI; Now when the callback function is called in Delphi, then the messagebox of aove code comeing correctly, but the GUI is "Not Responding" and form fields are not updated;
ANy clue why this is happening?

If any clarification required plz comment?
Any one give me the idea where I should declare the CallBackProc?

Thanks

Tags: Delphi