Just as a side not on this topic, Gerry wrote to me personally and I was able to gather that the "real" problem was that he was evidently attempting to use a library unit...one not part of his project...calling a procedure that would in turn need to reference an object in his project! And of course that's not a good idea because the library unit suddenly is no longer re-useable if you do that. The right way to handle this would be to change the procedure to a function with a return value his project can use. Then the library unit has no need to reference any unit of his project.
>From "Robert Meek" Personal e-mail: [EMAIL PROTECTED] dba / "Tangentals Design" Visit us at: www.TangentalsDesign.com Home of "The Keep"! Member of: "Association of Shareware Professionals" Moderator for: "The Delphi", "Delphi-DB", and "Delphi-Talk" programming lists at elists.org, and "DelphiTalk.net" at www.DelphiTalk.net -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Stephen Posey Sent: Tuesday, March 15, 2005 6:30 PM To: Borland's Delphi Discussion List Subject: Re: Pointer Usage Gerry Bendixen wrote: > Obviously I was not so clear on my goals. > Here's an attempt to provide an example, stripped of all non-essential details. Hopefully I present it correctly. > I have a 'main' unit (Main.pas) with a form. On the form is ProgressBar1 (a TProgressBar component) > I have a 'uses' unit (Unit1.pas) that does processing and the goal is to show the progress of this processing by updating the ProgressBar on the main form. > > (1) Type PProgressBar = ^TProgressBar ; //Declare pointer type > (2) Var ProgressBar1Ptr : PProgressBar ; //Declare pointer variable > (3) ProgressBar1Ptr := PProgressBar(ProgressBar1) ; //Assign value to pointer > (4) TProgressBar(ProgressBarPtr).Position := CalculatedBarPosition ; Ouch, that's kind of convoluted pointer usage, and really unnecessary with Delphi classes and objects. > Line 1 and 2 are visible to both Main and Unit1. > Line 3 is executed in Main to set the value to the pointer. > Line 4 is executed in Unit1 is update the position of the progress bar. That clarifies things a lot, thanks. You can refer to the progress bar using any of the techniques I mentioned in my previous email. Probably the simplest being to refer to the progress bar directly using the MainForm instance variable: MainForm.ProgressBar1.Position := CalculatedBarPosition; As I mentioned previously though, I'm leery of directly accessing components on a form from code in another unit. It increases module coupling and breaks the encapsulation barrier. My personal preference for a case like this would be either to add a method to MainForm from to update the progressbar and call that from the other code, e.g.: // in Main.pas type TMainForm = class(TForm) ProgressBar1 : TProgressBar; public procedure UpdateProgress(Value: Integer); end; var MainForm: TMainForm; implementation TMainFon.UpdateProgress(Value: Integer); begin ProgressBar1.Position := Value; end; ... // in Unit1.pas uses Main; ... MainForm.UpdateProgress(CalculatedBarPosition); Or (possibly better) make UpdateProgress an exported function of the unit: // in Main.pas type TMainForm = class(TForm) ProgressBar1 : TProgressBar; public end; procedure UpdateProgress(Value: Integer); var MainForm: TMainForm; implementation TMainFon.UpdateProgress(Value: Integer); begin MainForm.ProgressBar1.Position := Value; end; ... // in Unit1.pas uses Main; ... UpdateProgress(CalculatedBarPosition); In this way you encapsulate "progress updating" to a single place local to where it occurs. That allows you to easily change how progress is displayed or include other things that may need to be updated at the same time. For the latter case, you may want to add some code to make sure MainForm is instantiated, and do so if it isn't. HTH Stephen Posey [EMAIL PROTECTED] _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
