Raising Exception in TThread Execute?

Question

I just realized that my exceptions are not being shown to the user in my threads!

At first I used this in my thread for raising the exception, which does not work:

except on E:Exception do
begin
  raise Exception.Create('Error: ' + E.Message);
end;

The IDE shows me the exceptions, but my app does not!

I have looked around for a solution, this is what I found:

Delphi thread exception mechanism

http://www.experts-exchange.com/Programming/Languages/Pascal/Delphi/Q_22039681.html

And neither of these worked for me.

Here's my Thread unit:

unit uCheckForUpdateThread;

interface

uses
  Windows, IdBaseComponent, IdComponent, IdTCPConnection, IdTCPClient,
  IdHTTP, GlobalFuncs, Classes, HtmlExtractor, SysUtils, Forms;

type
  TUpdaterThread = class(TThread)
  private
    FileGrabber : THtmlExtractor;
    HTTP : TIdHttp;
    AppMajor,
    AppMinor,
    AppRelease : Integer;
    UpdateText : string;
    VersionStr : string;
    ExceptionText : string;
    FException: Exception;
    procedure DoHandleException;
    procedure SyncUpdateLbl;
    procedure SyncFinalize;
  public
    constructor Create;

  protected
    procedure HandleException; virtual;

    procedure Execute; override;
  end;

implementation

uses
  uMain;

{ TUpdaterThread }

constructor TUpdaterThread.Create;
begin
  inherited Create(False);
end;

procedure TUpdaterThread.Execute;
begin
  inherited;
  FreeOnTerminate := True;

  if Terminated then
    Exit;

  FileGrabber           := THtmlExtractor.Create;
  HTTP                  := TIdHTTP.Create(nil);
  try
    try
      FileGrabber.Grab('http://jeffijoe.com/xSky/Updates/CheckForUpdates.php');
    except on E: Exception do
    begin
      UpdateText := 'Error while updating xSky!';
      ExceptionText := 'Error: Cannot find remote file! Please restart xSky and try again! Also, make sure you are connected to the Internet, and that your Firewall is not blocking xSky!';
      HandleException;
    end;
    end;

    try
      AppMajor      := StrToInt(FileGrabber.ExtractValue('AppMajor[', ']'));
      AppMinor      := StrToInt(FileGrabber.ExtractValue('AppMinor[', ']'));
      AppRelease    := StrToInt(FileGrabber.ExtractValue('AppRelease[[', ']'));
    except on E:Exception do
    begin
      HandleException;
    end;
    end;

    if (APP_VER_MAJOR < AppMajor) or (APP_VER_MINOR < AppMinor) or (APP_VER_RELEASE < AppRelease) then
    begin
      VersionStr := Format('%d.%d.%d', [AppMajor, AppMinor, AppRelease]);
      UpdateText := 'Downloading Version ' + VersionStr;
      Synchronize(SyncUpdateLbl);
    end;

  finally
    FileGrabber.Free;
    HTTP.Free;
  end;
  Synchronize(SyncFinalize);
end;

procedure TUpdaterThread.SyncFinalize;
begin
  DoTransition(frmMain.TransSearcher3, frmMain.gbLogin, True, 500);
end;

procedure TUpdaterThread.SyncUpdateLbl;
begin
  frmMain.lblCheckingForUpdates.Caption := UpdateText;
end;

procedure TUpdaterThread.HandleException;
begin
  FException := Exception(ExceptObject);
  try
    Synchronize(DoHandleException);
  finally
    FException := nil;
  end;
end;

procedure TUpdaterThread.DoHandleException;
begin
  Application.ShowException(FException);
end;

end.

If you need more info just let me know.

Again: The IDE catches all the exceptions, but my program does not show them.

EDIT: It was Cosmin's solution that worked in the end - and the reason it didn't at first, was because I didn't add the ErrMsg variable, instead I just placed whatever the variable would contain into the Synchronize, which would NOT work, however I have NO idea why. I realized it when I had no other ideas, and I just messed around with the solutions.

As always, the joke's on me. =P

Answer 1

Here's my very, very short "take" on the issue. It only works on Delphi 2010+ (because that version introduced Anonymous methods). Unlike the more sophisticated methods already posted mine only shows the error message, nothing more, nothing less.

procedure TErrThread.Execute;
var ErrMsg: string;
begin
  try
    raise Exception.Create('Demonstration purposes exception');
  except on E:Exception do
    begin
      ErrMsg := E.ClassName + ' with message ' + E.Message;
      // The following could be all written on a single line to be more copy-paste friendly  
      Synchronize(
        procedure
        begin
          ShowMessage(ErrMsg);
        end
      );
    end;
  end;
end;