public int AddMaterial(FormCollection f)
 {
     try
     {
         ManageMaterialBusiness mmb = new ManageMaterialBusiness();
         string materialName = f["txtName"].ToString();
         string materialUnit = f.Get("txtUnit").ToString();
         int materialSQuantity = Convert.ToInt32(f["txtSQuantity"]);
         var materialList = mmb.GetMaterial();
         for (int i = 0; i < materialList.Count; i++)
         {
             if (StringComparer.CurrentCultureIgnoreCase.Equals(materialName, materialList[i].ProductMaterialName))
             {
                 //TempData["Error"] = String.Format("{0}{1}", materialName, " đã tồn tại");
                 return -2;
             }
         }
         if (ModelState.IsValid)
         {
             mmb.AddMaterial(materialName, materialUnit, materialSQuantity);
             return 1;
         }
         return -1;
     }
     catch
     {
         return -3;
     }
 }