BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  TList.Sort          BorlandTalk.com Forum Index -> Delphi ObjectPascal View previous topic :: View next topic   Author Message Mainlander Guest Posted: Tue Sep 23, 2003 12:08 am    Post subject: TList.Sort I have a class that I designed that contains some objects in its fields, that are derived from the TList class. I want to use the TList Sort procedure to sort the items that are in the derived class. The derived class has an extra field that specifies how to sort the items. The problem I have is in the implementation of the Sort method in the way the class is implemented by Borland. The call to the Sort method must pass in the name of a simple procedure. The procedure call then receives the pointers to the two items that it must return the order of. Why oh why could Borland have not implemented the sort procedure call as an event procedure or allow a method of another object to be passed as the parameter to the Sort call, because I want the sort procedure to be able to read the extra field in my class so that it knows how to carry out the sort. As the sort procedure does not receive any information about the calling object there are various un-OO fudges like global variables necessary to enable the sort procedure to get this information which I would like to eliminate. I have been able to discover that it is not possible to pass a class method in the sort procedure. Back to top Trevor Guest Posted: Wed Sep 24, 2003 7:00 pm    Post subject: Re: TList.Sort Mainlander <*@*.*> wrote in news:MPG.19da56351ab6fc42989d39 (AT) news (DOT) paradise.net.nz: Quote: I have a class that I designed that contains some objects in its fields, that are derived from the TList class. <snip> Quote: As the sort procedure does not receive any information about the calling object there are various un-OO fudges like global variables necessary to enable the sort procedure to get this information which I would like to eliminate. I have been able to discover that it is not possible to pass a class method in the sort procedure. It's just a callback function. This should work. function SizeCompare(objA, objB : pointer) : integer; begin if ((objA as TWhatever).Size > (objB as TWhatever).Size) then Result := 1 else if ((objA as TWhatever).Size < (objB as TWhatever).Size) then Result := -1 else Result := 0; end; -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- Back to top Mainlander Guest Posted: Wed Sep 24, 2003 9:36 pm    Post subject: Re: TList.Sort In article <Xns940098E61CB93trevorokesympaticoca (AT) 209 (DOT) 25.157.130>, [email]trevor.oke (AT) pullmyfinger (DOT) sympatico.ca[/email] says... Quote: Mainlander <*@*.*> wrote in news:MPG.19da56351ab6fc42989d39 (AT) news (DOT) paradise.net.nz: I have a class that I designed that contains some objects in its fields, that are derived from the TList class. snip As the sort procedure does not receive any information about the calling object there are various un-OO fudges like global variables necessary to enable the sort procedure to get this information which I would like to eliminate. I have been able to discover that it is not possible to pass a class method in the sort procedure. It's just a callback function. This should work. function SizeCompare(objA, objB : pointer) : integer; begin if ((objA as TWhatever).Size > (objB as TWhatever).Size) then Result := 1 else if ((objA as TWhatever).Size < (objB as TWhatever).Size) then Result := -1 else Result := 0; end; You miss the point. The objects passed in are items of a TList. The information I want is stored in a property of that TList. Unless there is a way of getting the TList object then it is a waste of time. The TStringList customsort method allows the object instance to be passed permitting this very thing. The TListView and TTreeview components both have an event handler defined, OnCompare, which of course passes the object instance as the Sender parameter. Back to top Jeremy Collins Guest Posted: Thu Sep 25, 2003 7:38 am    Post subject: Re: TList.Sort Mainlander wrote: Quote: You miss the point. The objects passed in are items of a TList. The information I want is stored in a property of that TList. Unless there is a way of getting the TList object then it is a waste of time. So write a TList descendent that uses a different Sort callback. -- jc Remove the -not from email Back to top Trevor Guest Posted: Thu Sep 25, 2003 5:05 pm    Post subject: Re: TList.Sort Mainlander <*@*.*> wrote in news:MPG.19dcd53efa034988989d46 (AT) news (DOT) paradise.net.nz: Quote: You miss the point. The objects passed in are items of a TList. The information I want is stored in a property of that TList. Unless there is a way of getting the TList object then it is a waste of time. The TStringList customsort method allows the object instance to be passed permitting this very thing. The TListView and TTreeview components both have an event handler defined, OnCompare, which of course passes the object instance as the Sender parameter. Ah. I see what you mean now. I'm going to agree with Jeremy and suggest that you just descend from TList and give it the functionality that you want. T -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- Back to top Mainlander Guest Posted: Thu Sep 25, 2003 11:24 pm    Post subject: Re: TList.Sort In article <8Ywcb.3836$%G1.766 (AT) newsfep4-winn (DOT) server.ntli.net>, [email]jd.collins (AT) ntlworld-not (DOT) com[/email] says... Quote: Mainlander wrote: You miss the point. The objects passed in are items of a TList. The information I want is stored in a property of that TList. Unless there is a way of getting the TList object then it is a waste of time. So write a TList descendent that uses a different Sort callback. How do I do that without the source code to TList? 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