Delphi, VirtualStringTree - classes (objects) instead of records

Question

I need to use a class instead of record for VirtualStringTree node.

Should I declare it standard (but in this case - tricky) way like that:

PNode = ^TNode;
TNode = record
 obj: TMyObject;
end;
//..
var
 fNd: PNode;
begin
fNd:= vstTree.getNodeData(vstTree.AddChild(nil));
fNd.obj:= TMyObject.Create; 
//..

or should I use directly TMyObject? If so - how?! How about assigning (constructing) the object and freeing it?

Thanks in advance m.

Answer 1

you could create the object instance after receiving the node data, as in :

fNd:= vstTree.getNodeData(vstTree.AddChild(nil)); 
fnd.obj := TMbyObject.Create;

or you could try and assign it directly

Pointer(Obj) := vstTree.getNodeData(...);

Answer 2

And you can free your object in OnFreeNode event.

Answer 3

Just add an object reference to your record. Use the OnInitNode and OnFreeNode events to create and destroy your object.

Answer 4

1. Setup datasize for holding object

   vstTree.NodeDataSize := SizeOf(TMyObject); 
   

2. Get the datasize holder and bind to your object

   vstTree.getNodeData(passed in interested node)^ := your object
   

   or

   vstTree.getNodeData(vstTree.AddChild(nil))^ := TMyObject.Create;
   

   or
   use vstTree.InsertNode method

3. To free the binding object hookup the OnFreeNode event

   vstTree.OnFreeNode := FreeNodeMethod;
   

   with

   procedure TFoo.FreeNodeMethod(Sender: TBaseVirtualTree; Node: PVirtualNode);
   var
     P: ^TMyObject;
   begin
     P := Sender.getNodeData(Node);
     if P <> nil then
     begin
         P^.Free;
         P^ := nil; //for your safety or you can omit this line
     end;
   end;
   

Answer 5

Hi the following code doesn't compile:

vstTree.getNodeData(passed in interested node)^ := your object

or

vstTree.getNodeData(vstTree.AddChild(nil))^ := TMyObject.Create;

Not at least in Delphi 2007. The following error pops up: "E2015 Operator not applicable to this operand type".

PS: I tried to post this as a comment to APZ28 but the link to comment wasn't avaiable.