Console Application Runner Classes Example 2: A better ExecAndWait

Applies to: ~>3.0

As noted in Example 1, it’s often worth letting a GUI program remain interactive - may be to display a progress bar or whatever.

To do this you need to handle TPJConsoleApp’s OnWork event.

Start a new Delphi GUI application and, in the form’s private section, insert the following new method declaration:

procedure WorkHandler(Sender: TObject);

Implement the method as follows:

procedure TForm1.WorkHandler(Sender: TObject);
begin
  Application.ProcessMessages;
end;

Now drop a TButton and add the following code as its OnClick event handler:

procedure TForm1.Button1Click(Sender: TObject);
var
  App: TPJConsoleApp;
begin
  App := TPJConsoleApp.Create;
  try
    App.MaxExecTime := INFINITE;  // don't time out
    App.TimeSlice := 100;         // yield to main app every 1/10 second
    App.Visible := True;          // ensure we see the app
    App.OnWork := WorkHandler;    // assign the event handler
    if not App.Execute('Timed 5') then  // run Timed.exe for 5 seconds
      ShowMessage('Failed to run Timed.exe');
  finally
    App.Free;
  end;
end;

The main code here is similar to Example 1 except that the TimeSlice property is now set to 100 rather than INFINITE and we have assigned a handler for the OnWork event. Setting TimeSlice forces the console app to yield to the GUI app every 1/10th of a second. When this happens TPJConsoleApp triggers the OnWork event, and our event handler lets the GUI application receive messages.

Run the program. Try to switch back to the GUI while the console app is running. Unlike in Example 1, you can now do it!

We’ve used Timed.exe from Appendix 2 once again. Substitute another suitable program if you wish, providing it runs for a significant amount of time.

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Console Application Runner Classes Example 2: A better ExecAndWait

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