处理带参数的存储过程

存储过程:
CREATE PROCEDURE Customer_Select
@country nvarchar(15)
AS
select CustomerID,CompanyName,ContactName from Customers where Country=@country
go

.aspx:
<form id="form1" runat="server">
<div>
 <asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" AutoPostBack="True">
<asp:ListItem Value="USA">USA</asp:ListItem>
<asp:ListItem Value="UK">UK</asp:ListItem>
<asp:ListItem Value="France">France</asp:ListItem>
<asp:ListItem Value="Canada">Canada</asp:ListItem>
<asp:ListItem Value="Norway">Norway</asp:ListItem>
</asp:DropDownList><br />
<asp:GridView ID="GridView1" runat="server">
</asp:GridView>
 </div>
</form>

.cs:
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
//创建连接字符串
string ConnString = "Data Source=.;Initial Catalog=Northwind;User ID=sa;Password=sa";

//创建操作对象
SqlDataAdapter adp = new SqlDataAdapter();

SqlCommand cmd = new SqlCommand();
cmd.Connection = new SqlConnection( ConnString);
DataTable dt = new DataTable();

//制定要调用的存储过程名称"Customer_Select";
//指定sqlcommand对象的命令类型为StoredProcedure 枚举类型
cmd.CommandText = "Customer_Select";
cmd.CommandType = CommandType.StoredProcedure;
//指定 SqlParameter对象,指定参数名称,数据类型 长度以及参数
SqlParameter para = new SqlParameter("@country",SqlDbType.NVarChar,15);
para.Value = DropDownList1.SelectedValue;
cmd.Parameters.Add(para);
//关联SqlDataAdapter和sqlcommand
adp.SelectCommand = cmd;
adp.Fill(dt);
GridView1.DataSource = dt;
GridView1.DataBind();

}