Regular procedure and method pointer

Posted on 2001-07-12
Medium Priority
Last Modified: 2008-03-17
I use an old unit, FastFileCopy to copy files.
The unit have declared a TCallBack
TCallBack = procedure (Position, Size: Integer; var Cancel: Boolean);

To use in this procedure call

procedure FastFileCopy(Const InFileName, OutFileName: String; CallBack: TCallBack);

How is it possible call the FastFileCopy procedure with a callback procedure located inanother object ?
Question by:koger
LVL 13

Expert Comment

ID: 6278983
To do that

TCallBack = procedure (Position, Size: Integer; var Cancel: Boolean);

should be

TCallBack = procedure (Position, Size: Integer; var Cancel: Boolean) of Object;
LVL 11

Expert Comment

ID: 6279459
I would not use such an method callback.
Adding a method callback to an otherwise function orinented API is not a good idea.
Either change the whole API to a class and make the callback an event or stay with the old API.

Accepted Solution

scrapdog earned 300 total points
ID: 6279621
If you don't want to change the old unit, you can wrap your method in normal procedure.

procedure MyProcedure(Position, Size: Integer; var Cancel: Boolean);
   MyObject.Method(Position, Size, Cancel);

and then use MyProcedure as the callback function.

You could also use a class procedure if you desired, but you would still qualify the method with an instance of the class.

This would constitute poor programming practice, so if you have the option of changing the old unit, you are better off to go with Epsylon's suggestion.

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

LVL 20

Expert Comment

ID: 6279649
Just to add another suggestion:


Regards, Madshi.
LVL 27

Expert Comment

ID: 6279670
points are yours, i guess,
as i know you helped me with a similar q

meikl ;-)

Expert Comment

ID: 6279680
In using MethodToProcedure:

Where does the method get the self pointer when it is called?  Is this magical?

Expert Comment

ID: 6279683
Ahh, I am assuming that it dynamically creates a procedure like the one I have written above...
LVL 20

Expert Comment

ID: 6279919
Right, scrappy...  :-)

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

A lot of questions regard threads in Delphi.   One of the more specific questions is how to show progress of the thread.   Updating a progressbar from inside a thread is a mistake. A solution to this would be to send a synchronized message to the…
This is an update to some code that someone else posted on Experts Exchange. It is an alternate approach, I think a little easier to use, & makes sure that things like the Task Bar will update.
The video will let you know the exact process to import OST/PST files to the cloud based Office 365 mailboxes. Using Kernel Import PST to Office 365 tool, one can quickly import numerous OST/PST files to Office 365. Besides this, the tool also comes…
To export Lotus Notes to Outlook PST or Exchange and Domino Server files to Exchange Server or PST files with ease, go for Kernel for Lotus Notes to Outlook conversion tool. Through the video, you can watch the conversion process. A common user with…

627 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question