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function IsTreeviewFullyExpanded( tv: TTreeview ): boolean;

var

  Node: TTreeNode;

begin

   Assert( Assigned( tv ) );

   if tv.Items.Count > 0 then

   begin

      Node := tv.Items[0];

      Result := true;

      while Result and Assigned( Node ) do

      begin

         Result := Node.Expanded or not Node.HasChildren;

         Node := Node.GetNext;

      end;

   end

   else

      Result := false;

end;

procedure TMainFrm.Button1Click(Sender: TObject);

begin

   if IsTreeviewFullyExpanded( TreeView1 ) then

      ShowMessage( 'TTreeView полностью развернут' );

end;