2

If a SendMessageTimeout call fails (i.e., returns 0), but a subsequent GetLastError returns 0 (success), is there any way to determine why the call failed?

The code I'm using (below) works fine for dozens of our users but for two users the SendMessageTimeout fails as described in the first sentence above. 

function TQBInfo.GetFormCellText(bTestForCaret: boolean = True): string;
const
  BUFSIZE = 4096;
  TIMEOUT_MSECS = 4000;
var
  Wnd: HWnd;
  dwResult: DWORD;
  buf: array of char;
  sLastErrorText: string;
begin
  Result := '';

  Wnd := GetEditControlWindow;          //Custom function to find the target window
  if Wnd = 0 then
    exit;

  SetLastError(0);
  FLastError_GetFormCellText := 0;      //FLastError_GetFormCellText is an object field
  SetLength(buf, BUFSIZE + 1);
  if SendMessageTimeout(Wnd, WM_GETTEXT, BUFSIZE + 1, LongInt(@buf[0]),
      SMTO_ABORTIFHUNG or SMTO_BLOCK,
      TIMEOUT_MSECS,
      dwResult) = 0 then begin                 //0 = Failed or timed out
    FLastError_GetFormCellText := GetLastError;
    //...at this point, FLastError_GetFormCellText is always 0 in the failure case I'm seeing
    if FLastError_GetFormCellText = ERROR_TIMEOUT then
      sLastErrorText := 'ERROR_TIMEOUT'
    else
      sLastErrorText := SysErrorMessage(FLastError_GetFormCellText);
...
4

0 回答 0