Selected value is not fill in Dropdown list c# mvc

Question

Hi, I want to edit my product so I have a three dropdown when I click Edit Button product load and Run this function Edit Product data load in result variable but not shown on the front end.  I have shared the result of data in the image. a kindly expert can you tell me where I am wrong.

 

 

Model

   public class ProductViewModel
    {

       public Product listProducts = new Product();
        public List listProductDetails = new List();
}

 Function c# 

public ActionResult EditProduct(int id)
        {
            List PTlist = _IproductType.PTList();
            ViewBag.Ptlist = new SelectList(PTlist, "PType_ID", "P_Name");

            //Product Color List
            List pColorList = _IProductColor.PColorlist();
            ViewBag.pColor_List = new SelectList(pColorList, "C_ID", "C_Name_OR_Code");

            List pSizeList = _ISize.pSizeList();
            ViewBag.pSizeLists = new SelectList(pSizeList, "S_ID", "S_Size");

            var result = _IProducts.GetProductByID(id);

            return View(result);
        }

 Result  

 

view

<div class="form-group">
                                    <label class="control-label col-lg-3"><span data-toggle="tooltip" class="label-tooltip" data-original-title="Product type"> Product Category </span></label>
                                    <div class="col-lg-9">
                                        <div class="col-sm-9 controls">
                                            @if (ViewBag.Ptlist != null)
                                            {
                                                @Html.DropDownListFor(m => m.listProducts.PType_ID, ViewBag.Ptlist as SelectList, "Choose Product Category", new { @class = "", @id = "PTypeID" })
                                            }
                                        </div>

                                    </div>
                                </div>
                                <div class="form-group">
                                    <label class="control-label col-lg-3"><span data-toggle="tooltip" class="label-tooltip" data-original-title="Product type"> Product Color </span></label>
                                    <div class="col-lg-9">
                                        <div class="col-sm-9 controls">
                                            @if (ViewBag.pColor_List != null)
                                            {
                                                @Html.DropDownListFor(m => m.listProducts.P_Color_ID, ViewBag.pColor_List as SelectList, "Choose Product Color", new { @class = "", @id = "PColorID" })
                                            }
                                        </div>

                                    </div>
                                </div>
                                <div class="form-group">
                                    <label class="control-label col-lg-3"><span data-toggle="tooltip" class="label-tooltip" data-original-title="Product type"> Product Size </span></label>
                                    <div class="col-lg-9">
                                        <div class="col-sm-9 controls">
                                            @if (ViewBag.pSizeLists != null)
                                            {
                                                @Html.DropDownListFor(m => m.listProducts.P_SizeID, ViewBag.pSizeLists as SelectList, "Choose Product Size", new { @class = "", @id = "PSizeID" })
                                            }
                                        </div>

                                    </div>
                                </div>