如何使用我用下面的代碼首先從<code>category entity</code>檢索<code>category Id</code>並將其綁定到<code>dropdownlist</code>是<code>DropDownlistCategory</code>。現在我想插入<code>category ID</code>從下拉列表產品asp.net實體數據模型

Question

插入選擇下拉列表值到數據庫實體包含在數據庫中的四列如

ProductName,CategoryID,QuantityPerUnit and UnitPrice. 

但同時插入下拉列表值將始終選擇從下拉列表的第一個值。

使用此：

prod.CategoryID = Convert.ToInt32(DropDownListCategory.SelectedValue);

它是正確的嗎？

NewProduct.aspx代碼： -

<asp:DropDownList ID="DropDownListCategory" runat="server"CssClass="form- control" Width="100px" OnSelectedIndexChanged="DropDownListCategory_SelectedIndexChanged" > 

    </asp:DropDownList> 

NewProduct.cs代碼： -

LaunderDBEntities context = new LaunderDBEntities(); 
    protected void Page_Load(object sender, EventArgs e) 
    { 

     var categoryId = from cat in context.Categories 
         select new 
         { 

          categoryID = cat.CategoryID, 

         }; 


     DropDownListCategory.DataSource = categoryId.ToList(); 
     DropDownListCategory.DataValueField = "categoryID"; 
     DropDownListCategory.DataTextField = "categoryID"; 
     DropDownListCategory.DataBind(); 
    } 
    protected void btnAddProduct_Click(object sender, EventArgs e) 
    { 
     SaveProductInfo(); 
    } 


    private void SaveProductInfo() 
    { 
     Product prod = new Product(); 
     prod.ProductName = txtProductName.Text; 

     prod.CategoryID = Convert.ToInt32(DropDownListCategory.SelectedValue); 

     prod.QuantityPerUnit = Convert.ToInt32(txtQuantity.Text); 
     prod.UnitPrice =Convert.ToInt32(txtUnitPrice.Text); 


     ProductDA prdDa = new ProductDA(); 
     prdDa.InertProductDetails(prod); 

     Label5.Text = "<p style='color:Green;'>Information Successfully saved!</p>"; 

     Response.Redirect("ProductInfo.aspx"); 

    } 

Answer 1

使用IsPostBack在頁面加載。僅在第一次加載頁面時綁定下拉列表。

protected void Page_Load(object sender, EventArgs e) 
{ 
     if(!IsPostBack) 
     { 
      //.... code to bind the dropdownlist 

     } 
}