WM_GETTEXT problem

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
  EnumChildWindows(Self.Handle, @EnumTextChildProc, 0);
end;

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unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private-Deklarationen }
    function nGetChildHandle: Integer;
  public
    { Public-Deklarationen }
  end;

function EIFindChildWindow(hwndParent: HWnd; ClassName: PChar): HWnd;
function EIGetWindowClass(const nHandle: HWnd): string;

var
  Form1: TForm1;

implementation

var
  hwndFindChildWindow : HWND;


{$R *.dfm}

function EnumTextChildProc(AHandle: hWnd): BOOL; stdcall;
var
  AText: array[0..255] of Char;
  s: string;
begin
  Result := True;
  PostMessage(AHandle, WM_GETTEXT, Sizeof(AText), integer(@AText));
  s := strpas(AText);
  ShowMessage(s);
end;

function GetTextFromHandle(wndhandle: HWnd): string;
var
 textlength: integer;
 text: PChar;
begin
   result := '';
   if wndhandle = 0 then Exit;
   textlength := SendMessage(wndhandle, WM_GETTEXTLENGTH, 0, 0);
   if textlength <> 0 then
     begin
       GetMem(Text, textlength+1);
       SendMessage(wndhandle, WM_GETTEXT, textlength+1, Integer(text));
       Result := text;
       FreeMem(text);
     end;

end;

function EIGetWindowClass(const nHandle: HWnd): string;
var
  szClassName: array[0..255] of char;
begin
  GetClassName(nHandle, szClassName, 255);
  Result := szClassName;
end;

function EnumWindowsForFindChildWindowProc(WHandle: HWND; lParam: LPARAM): BOOL; export; stdcall;
const
  MAX_WINDOW_NAME_LEN = 80;
var
  sTargetClassName: string;
  nHandle: HWnd;
  sCurrClassName: string;
  bResult: Boolean;
begin
  if (hwndFindChildWindow<>0) then
    exit;
  sTargetClassName := PChar(lParam);
  sCurrClassName := EIGetWindowClass(WHandle);
  bResult := CompareText(sCurrClassName, sTargetClassName) = 0;
  If (bResult) then
    hwndFindChildWindow := WHandle
  else
    EIFindChildWindow(WHandle, PChar(lParam));
end;

function EIFindChildWindow(hwndParent: HWnd; ClassName: PChar) : HWnd;
begin
  try
    EnumChildWindows(hwndParent, @EnumWindowsForFindChildWindowProc, LongInt(PChar(ClassName)));
    Result := hwndFindChildWindow;
  except
    on Exception do
      Result := 0;
  end;
end;

function TForm1.nGetChildHandle: Integer;
var
  nParentHandle: HWnd;
  nChildHandle: HWnd;
begin
  //Find parent window
  nParentHandle := FindWindow(nil, PChar('Your window title'));
  if nParentHandle = 0 then
    raise Exception.Create('Couldn''t find the main window !');

  //Find child window (TEdit)
  nChildHandle := EIFindChildWindow(nParentHandle, PChar('TEdit'));
  if nChildHandle = 0 then
    raise Exception.Create('Couldn''t find the child window !');

  Result := nChildHandle;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  TheChildHandle: hwnd;
begin
  TheChildHandle:=nGetChildHandle;
end;

end.

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