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Article #17665: Using the Application's OnIdle Event.

 Question and Answer Database

FAQ2665D.txt   Using the Application's OnIdle Event.
Category   :VCL
Platform    :All
Product    :All 32 bit  

Question:
How do I have my application perform work when the computer 
is idle?


Answer:
You can create an OnIdle event to be called whenever your
application is waiting for messages to be processed. Simply 
declare the event handler procedure in the private section 
of the forms declaration:

{ Private declarations }
procedure IdleEventHandler(Sender: TObject; var Done: Boolean);

In then implementation section, define the procedure:

procedure TForm1.IdleEventHandler(Sender: TObject;
  var Done: Boolean);
begin
 {Do a small bit of work here}
  Done := false;
end;

Then assign the Application's OnIdle event to point to your
new procedure(You may do this whereever you like, but a good
place would be the Forms OnCreate method):

Application.OnIdle := IdleEventHandler;

OnIdle is called only once, as the application transitions 
into an idle state. It is not called continuiously unless 
Done is set to False If Done is False, WaitMessage is not 
called. Applications that set Done to False consume an 
inordinate amount of CPU time that affects overall system 
performance.

You can set the boolean variable "done" to true when you want 
to stop the event handler from executing.

7/16/98 4:31:28 PM
 

Last Modified: 01-SEP-99