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Does TTreeNode.Data need to be disposed of?

Posted on 2002-03-25
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Last Modified: 2008-02-26
Hi, I am populating TreeView with File Names and I use
the TTreeNode.Data property to point at strings
containing each File Name's path.

procedure TForm1.GetFiles(tree:TTreeView; pn: TTreeNode; fp:string);
//pn=parent node, fp=folder path, tn=temp node
var sr: TSearchRec;
    ps: ^string;
    tn: TTreeNode;
begin
  AddLastSlash(fp);
  if FindFirst(fp + '*.jpg', faArchive, sr) = 0 then
  begin
    repeat
      if ((sr.Attr and faArchive) = faArchive) then
      begin

        new(ps);
        ps^:= fp + sr.name;
        tn := tree.Items.AddChildObject(pn, sr.Name, ps);

        tn.ImageIndex := 6;
        tn.SelectedIndex := 6;
      end;
    until FindNext(sr) <> 0;
    FindClose(sr);
  end;
end;

My question is:  Do I have to call Dispose(Node.Data)
before I use Node.Delete, Node.DeleteChildren or
Tree.Items.Clear methods?  

I tried it with and without Dispose, there seems to be no
problem either way, so what is the right way?
Thanks
cj
0
Comment
Question by:czechmate
7 Comments
 
LVL 1

Expert Comment

by:Fraction
ID: 6895007
I don't think the dispose memory for node data is done automaticly when you delete a node, but when your application terminates I think it disposes all allocated memory. But a simple way to do this is to add the dispose memory code to the TreeView Deletion event.

procedure TForm1.TreeView1Deletion(Sender: TObject; Node: TTreeNode);
begin
 Dispose(Node.Data);
end;
0
 
LVL 1

Expert Comment

by:Fraction
ID: 6895015
I don't think the dispose memory for node data is done automaticly when you delete a node, but when your application terminates I think it disposes all allocated memory. But a simple way to do this is to add the dispose memory code to the TreeView Deletion event.

procedure TForm1.TreeView1Deletion(Sender: TObject; Node: TTreeNode);
begin
 Dispose(Node.Data);
end;
0
 
LVL 1

Author Comment

by:czechmate
ID: 6895031
Thanks Fraction, I know about this event I've used it.  
The question really is does one have to do it or not :)

Delphi Help says:
When an application is finished using a dynamic variable
created with New, it should dispose of the memory allocated for the variable using the Dispose standard procedure.

I would think that if it is used with parent-less
structures like linked lists than yes.  
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LVL 26

Expert Comment

by:Russell Libby
ID: 6895067

The simple answer is yes.
The Delphi compiler makes no assumptions about the contents held in the the Data property, other than the fact its a pointer. (it could be a pointer to an object,  record type, record type with pointers to allocated memory, etc..). So you, as the programmer, are left with the resposibility of releasing any allocated memory.

Russell
0
 
LVL 1

Expert Comment

by:Fraction
ID: 6895082
I think you can ignore disposing memory, and run your application without any problem for some time, but you can't assume that the user should exit your application frequently just to free memory. If you keep adding and removing nodes to your tree view sooner or later you will run out of memory.
0
 

Accepted Solution

by:
classics earned 150 total points
ID: 6895567
In the destructor for TTreeNode, Data is simply set to Nil without checking its value.  Anything you associate with this pointer should be freed before destroying the node.
0
 
LVL 1

Author Comment

by:czechmate
ID: 6895713
To Classics:
I am going to accept your proposed answer since it looks technically correct.  However, I would like to remind you, it is much more friendy to post your response as a comment and thus give chance to other experts to contribute or voice their opinion.  
Regards
cj
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