Loading .OBJ 3D files

While I'm still just beginning here also, this seems to work (converted from VB.net).

Model3DGroup MdlGrp = null;
switch (Path.GetExtension(FilDia.FileName).ToUpper) {
    case ".3DS":
        StudioReader ObjRed = new StudioReader();
        MdlGrp = ObjRed.Read(FilDia.FileName);
        break;
    case ".LWO":
        LwoReader ObjRed = new LwoReader();
        MdlGrp = ObjRed.Read(FilDia.FileName);
        break;
    case ".OFF":
        OffReader ObjRed = new OffReader();
        MdlGrp = ObjRed.Read(FilDia.FileName);
        break;
    case ".OBJ":
        ObjReader ObjRed = new ObjReader();
        //ObjRed.DefaultMaterial = UseMat
        MdlGrp = ObjRed.Read(FilDia.FileName);
        break;
    case ".STL":
        StLReader ObjRed = new StLReader();
        MdlGrp = ObjRed.Read(FilDia.FileName);
        break;
}

Thanks a lot :)

My code is this. Please help me to integrate with your code. Thanks in advance :)

using HelixToolkit.Wpf;
using System;
using System.IO;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media.Media3D;
namespace Display3DModel
{
    public partial class MainWindow : Window
    {
        private const string MODEL_PATH = "D:/vs/display3D-master/Display3DModel/bicycle.stl";
        public object FilDia { get; private set; }
        public MainWindow()
        {
            InitializeComponent();
            Model3DGroup MdlGrp = null; 

            ModelVisual3D device3D = new ModelVisual3D();
            device3D.Content = Display3d(MODEL_PATH);
            viewPort3d.Children.Add(device3D);         
        }
        private Model3D Display3d(string model)
        {
            Model3D device = null;
            try
            {
                Console.WriteLine("Hello!!!");
                viewPort3d.RotateGesture = new MouseGesture(MouseAction.LeftClick);
                ModelImporter import = new ModelImporter();
                device = import.Load(model);
            }
            catch (Exception e)
            {       
                MessageBox.Show("Exception Error : " + e.StackTrace);
            }
            return device;
        }     
    }
}

Something like this:

      Model3DGroup MdlGrp = null;
      ModelVisual3D device3D = new ModelVisual3D();
      ObjReader ObjRed = new ObjReader();
      MdlGrp = ObjRed.Read(MODEL_PATH);
      device3D.Content = MdlGrp;
      ViewWindow.Children.Add(device3D);
      ViewWindow.Children.Add(new DefaultLights());
      ViewWindow.ZoomExtents(0.0);