Add new product. How to make First Catagory to be selected by default.

I had the same problem, here is what I have done :

1- Open

NopCommerceStore\Administration\Modules\ProductInfoAdd.ascx.cs

2- Search for

this.ddlTaxCategory.Items.Clear();

       line 72
3- You will find a foreach like this line 90 :

foreach (TaxCategory taxCategory in taxCategoryCollection)
            {
                ListItem item2 = new ListItem(taxCategory.Name, taxCategory.TaxCategoryId.ToString());
                this.ddlTaxCategory.Items.Add(item2);
            }

4- Add those lines after the foreach at line 81

            //Added by Mena Bassily
                this.ddlTaxCategory.Items[1].Selected = true;            
            //End of Added by Mena Bassily

Now go to Configuration - Tax - Tax Classes, Open the wanted TaxClass and give it Display Order = 1

Don't forget to add the commented lines as well in the ProductVariantInfo.ascx.cs

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                this.FillDropDowns();
                this.BindData();
                //Added by Mena Bassily
                      this.ddlTaxCategory.Items[1].Selected = true;            //line 252
                //End of Added by Mena Bassily
            }
        }

Sorry about the last reply, it contains an error, the right way it to edit ProductVariantInfo.ascx.cs

and add :

                //Added by Mena Bassily
                      this.ddlTaxCategory.Items[1].Selected = true;            //line 252
                //End of Added by Mena Bassily

after :

 this.ddlTaxCategory.Items.Clear();
            ListItem itemTaxCategory = new ListItem("---", "0");
            this.ddlTaxCategory.Items.Add(itemTaxCategory);
            var taxCategoryCollection = TaxCategoryManager.GetAllTaxCategories();
            foreach (TaxCategory taxCategory in taxCategoryCollection)
            {
                ListItem item2 = new ListItem(taxCategory.Name, taxCategory.TaxCategoryId.ToString());
                this.ddlTaxCategory.Items.Add(item2);
            }

Thanks mb. Like it
I hope it will be changed  for next version (all admin dropdown list)

I'm watching this post : https://www.nopcommerce.com/boards/t/4106/add-new-product-how-to-make-first-catagory-to-be-selected-by-default.aspx