c# - WPF with Helix toolkit, animate with code-behind? -

i new wpf, , trying build 3d viewport helix toolkit. viewport, grid etc show expected, , add simple tube. now, want use new function update transform of tube, based on user input, cannot work.

where going wrong here?

thank you.

.xaml

  <usercontrol x:class="wpfusercontrol.usercontrol1"              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"              xmlns:helixtoolkit="clr-namespace:helixtoolkit.wpf;assembly=helixtoolkit.wpf"               mc:ignorable="d"              d:designheight="480" d:designwidth="640">     <grid>         <!-- helixviewport3d supports camera manipulation, , can used viewport3d -->         <helixtoolkit:helixviewport3d zoomextentswhenloaded="true" name="mainviewport">              <helixtoolkit:sunlight/>              <modelvisual3d content="{binding model}"/>              <helixtoolkit:gridlinesvisual3d width="40" length="40" minordistance="1" majordistance="1" thickness="0.01"/>          </helixtoolkit:helixviewport3d>     </grid> </usercontrol> 

.xaml.cs

using helixtoolkit.wpf;  namespace wpfusercontrol {     /// <summary>     /// interaction logic usercontrol1.xaml     /// </summary>     public partial class usercontrol1 : usercontrol     {         public tubevisual3d tube1 = new tubevisual3d();          public usercontrol1()         {              initializecomponent();             datacontext = this;             setup();          }           public void settranslation(double xx) //this called external app.         {               console.write(xx); //this prints expected.              //translatetransform3d trans = new translatetransform3d(new vector3d(xx, 0, 0));                //  tube1.transform = trans;  //this not work.          }          public void setup()         {                          int tubediameter = 5;             tube1.path = new point3dcollection();             tube1.path.add(new point3d(-15, 0, 0));             tube1.path.add(new point3d(15, 0, 0));             tube1.diameter = tubediameter;             tube1.fill = brushes.red;             tube1.ispathclosed = false;              mainviewport.children.add(tube1);          }      } }