Question

I want to browse through XML using a TTreeView. To associate the treeview nodes with the XML nodes with attributes I used the following syntax:

var tv: TTreeView; tn1, tn2: TTreeNode; xn: IXMLNode;

if xn.AttributeNodes.Count > 0 then
  tn2 := tv.Items.AddChildObject( tn1, xn.NodeName, @xn )
else
  tn2 := tv.Items.AddChild( tn1, xn.NodeName );

.. and later in the program:

var  tv: TTreeView; pxn: ^IXMLNode; i: integer;

pxn := tv.Selected.Data;
for i := 0 to iXML.AttributeNodes.Count-1 do
  ShowMessage ( pxn^.AttributeNodes[i].LocalName + ' = ' +
                pxn^.AttributeNodes[i].Text );

which results in an exception.. As far as I can figure out this has to do with the fact that I’m point to an interface instead of an object.

Is it possible to reference the actual object of the XML instead of the interface?
What will happen with this reference if new XML nodes are inserted in or deleted from the tree?

Or is there another straight forward solution?

All help appreciated!

Answer 1

don’t use @ and ^ operators, interfaces are already references

first code:

var tv: TTreeView; tn1, tn2: TTreeNode; xn: IXMLNode;

if xn.AttributeNodes.Count > 0 then
  tn2 := tv.Items.AddChildObject( tn1, xn.NodeName, Pointer(xn) )
else
  tn2 := tv.Items.AddChild( tn1, xn.NodeName );

second code (don’t forget to check if data is assigned)

var  tv: TTreeView; pxn: IXMLNode; i: integer;

if Assigned(tv.Selected) and Assigned(tv.Selected.Data) then begin
  pxn := IXMLNode(tv.Selected.Data);
  for i := 0 to iXML.AttributeNodes.Count-1 do
    ShowMessage ( pxn.AttributeNodes[i].LocalName + ' = ' +
                  pxn.AttributeNodes[i].Text );
end;

Just search in the net for more information about interfaces, classes and the differences between them. Good information: http://blog.synopse.info/post/2012/02/29/Delphi-and-interfaces