procedure TForm1.Button1Click(Sender: TObject);

var

  hEdit: HWND;

  str: string;

begin

  str := '准备要添加到记事本的字符串';

  WinExec('Notepad.exe', SW_SHOWNORMAL);

  hEdit := GetWindow(GetForegroundWindow, GW_CHILD);

  SendTextMessage(hEdit, WM_SETTEXT, 0, str);

end;

{$IFNDEF UNICODE}

function SendTextMessage(Handle: HWND; Msg: UINT; WParam: WPARAM; LParam: AnsiString): LRESULT;

begin

  Result := SendMessage(Handle, Msg, WParam, Windows.LPARAM(PAnsiChar(LParam)));

end;

{$ENDIF}

function SendTextMessage(Handle: HWND; Msg: UINT; WParam: WPARAM; LParam: UnicodeString): LRESULT;

begin

  Result := SendMessage(Handle, Msg, WParam, Windows.LPARAM(PWideChar(LParam)));

end;

function SendStructMessage(Handle: HWND; Msg: UINT; WParam: WPARAM; const LParam): LRESULT;

begin

  Result := SendMessage(Handle, Msg, WParam, Windows.LPARAM(@LParam));

end;

function SendGetStructMessage(Handle: HWND; Msg: UINT; WParam: WPARAM;

  var LParam; Unused: Boolean = False): LRESULT;

begin

  Result := SendMessage(Handle, Msg, WParam, Windows.LPARAM(@LParam));

end;

function SendGetIntMessage(Handle: HWND; Msg: UINT; var WParam: Integer;

  var LParam: Integer): LRESULT;

begin

  Result := SendMessage(Handle, Msg, Windows.WPARAM(@WParam), Windows.LPARAM(@LParam));

end;

{用 API 实现的获取文本容器中选择的文本的函数}

function GetEditSeleteText(h: HWND): string;

var

  len,sx,ex: Integer; {文本总长度, 选择的开始位置, 选择的结束位置}

  buf: PChar;         {所有文本}

begin

  {获取文本总长度}

  len := SendMessage(h, WM_GETTEXTLENGTH, 0, 0) + 1;

  {为接受所有文本的缓冲区分配内存}

  buf := GlobalAllocPtr(0, len); {这里没有使用 GetMem, 因为需要全局的, 不然无法面对其他程序}

  {获取所有文本}

  SendMessage(h, WM_GETTEXT, len, Longint(buf));

  {获取选择的开始位置和结束位置}

  SendMessage(h, EM_GETSEL, Longint(@sx), Longint(@ex));

  {截取选择的文本}

  Result := Copy(buf, sx+1, ex-sx);

  {释放内存}

  GlobalFreePtr(buf);

end;

{测试 TEdit, 同时与 VCL 的获取方法对比}

procedure TForm1.Button1Click(Sender: TObject);

begin

  ShowMessage(GetEditSeleteText(Edit1.Handle) + ' - ' + Edit1.SelText);

end;

{测试 TMemo, 同时与 VCL 的获取方法对比}

procedure TForm1.Button2Click(Sender: TObject);

begin

  ShowMessage(GetEditSeleteText(Memo1.Handle) + ' - ' + Memo1.SelText);

end;

{测试 TRichEdit, 同时与 VCL 的获取方法对比}

procedure TForm1.Button3Click(Sender: TObject);

begin

  ShowMessage(GetEditSeleteText(RichEdit1.Handle) + ' - ' + RichEdit1.SelText);

end;