Keep app responsive during long task

Question

A certain form in our application displays a graphical view of a model. The user can, amongst loads of other stuff, initiate a transformation of the model that can take quit

Answer 1

If you can split your transformation code into little chunks, then you can run that code when the processor is idle. Just create an event handler, hook it up to the Application.OnIdle event. As long as you make sure that each chunk of code is fairly short (the amount of time you want the application to be unresponsive...say 1/2 a second. The important thing is to set the done flag to false at the end of your handler :

procedure TMyForm .IdleEventHandler(Sender: TObject;
  var Done: Boolean);
begin
  {Do a small bit of work here}
  Done := false;
end;

So for example if you have a loop, instead of using a for loop, use a while loop, make sure the scope of the loop variable is at the form level. Set it to zero before setting the onIdle event, then for example perform 10 loops per onidle hit until you hit the end of the loop.

Count := 0;
Application.OnIdle := IdleEventHandler;

...
...

procedure TMyForm .IdleEventHandler(Sender: TObject;
  var Done: Boolean);
var
  LocalCount : Integer;
begin
  LocalCount := 0;

  while (Count < MaxCount) and (Count < 10) do
  begin
    {Do a small bit of work here}
    Inc(Count);
    Inc(LocalCount);
  end;
  Done := false;
end;