关于TTreeView的问题。(50分)

这是我做的一个TTreeView的拖动的例子。
界面上只有一个TTreeView，随便加了些结点，都带有子结点。

var
sourcetreenode: TTreeNode;

procedure TForm1.TreeView1DragDrop(Sender, Source: TObject; X, Y: Integer);
var
tempnode, targetTreeNode: TTreeNode;
begin
tempnode:= treeview1.Items.AddChild(treeview1.droptarget, '');
tempnode.Assign(sourcetreenode);
sourcetreenode.Free;
end;

procedure TForm1.TreeView1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
accept:= True;
end;

procedure TForm1.TreeView1StartDrag(Sender: TObject;
var DragObject: TDragObject);
begin
sourcetreenode:= treeview1.Selected;
end;


结果是将一个带子结点的结点拖动到另一个结点做为其子结点时，新子结点有展开的符号可是展不开。
恳请大虾门指正

procedure TForm1.TreeView1DragDrop(Sender, Source: TObject; X,
Y: Integer);
var toBoxID, sMailID: String;
i : integer;
AnItem: TTreeNode;
AttachMode: TNodeAttachMode;
HT: THitTests;
begin
if TreeView1.Selected = nil then Exit;

HT := TreeView1.GetHitTestInfoAt(X, Y);
AnItem := TreeView1.GetNodeAt(X, Y);
if (HT - [htOnItem, htOnIcon, htNowhere, htOnIndent] <> HT) then
begin
if (htOnItem in HT) or (htOnIcon in HT) then AttachMode := naAddChild
else if htNowhere in HT then AttachMode := naAdd
else if htOnIndent in HT then AttachMode := naInsert
else AttachMode :=naAdd;

TreeView1.Selected.MoveTo(AnItem, AttachMode);
end;

end;

非常感谢！