TApplication.OnException Event

Occurs when an unhandled exception occurs in the application.

Pascal

property OnException: TExceptionEvent;

C++

__property TExceptionEvent OnException;

Description

Use OnException to change the default behavior that occurs when an exception is not handled by application code. The OnException event handler is called automatically in the HandleException method.

OnException only handles exceptions that occur during message processing. Exceptions that occur before or after the execution of the application's Run method do not generate OnException events.

If an exception passes through the tryblocks in the application code, the application automatically calls the HandleException method. Unless the exception object is EAbort, HandleException calls the OnException handler, if one exists. Otherwise, it calls ShowException to display a message box indicating an error occurred.

TExceptionEvent is the type of the OnException event. It points to a method that handles exceptions in the application. The Sender parameter is the object that raised the exception, and E is the exception object.

Note: You can also respond to this event using the TApplicationEvents component, which allows you to assign an event handler using the IDE.

C++ Examples:

Copy Code

/*
In addition to displaying the exception message, which
happens by default, the following code shuts down the 
application when an exception is not caught and handled.
AppException should be declared a method of TForm1.
*/

#include <System.hpp>
#include <SysUtils.hpp>

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  Application->OnException = AppException;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::AppException(TObject *Sender, Exception *E)
{
  Application->ShowException(E);
  Application->Terminate();
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  throw(Exception("Hardware error: Divide by 0"));
}

Delphi Examples:

Copy Code

{
In addition to displaying the exception message, which 
happens by default, the following code shuts down the 
application when an exception is not caught and handled.  
AppException should be declared a method of TForm1.
}
procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnException := AppException;
end;
procedure TForm1.AppException(Sender: TObject; E: Exception);
begin
  Application.ShowException(E);
  Application.Terminate;
end; 

procedure TForm1.Button1Click(Sender: TObject);
begin
  raise EPasswordInvalid.Create('Incorrect password entered');
end;