Gridview中的编辑模板与项模板的用法

 <asp:GridView ID="GridView1" AutoGenerateColumns="false" runat="server" BorderColor="Black"
            onrowcancelingedit="GridView1_RowCancelingEdit" 
            onrowediting="GridView1_RowEditing" 
            onrowdatabound="GridView1_RowDataBound" onrowupdating="GridView1_RowUpdating">
            <Columns>
                <asp:TemplateField HeaderText ="ID">
                    <ItemTemplate>
                        <%#Eval("CustomerID") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                    <%#Eval("CustomerID") %>
                    </EditItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText ="Name">
                    <ItemTemplate>
                        <%#Eval("CompanyName") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox ID="TextBox1" runat="server" Text ='<%#Eval("CompanyName") %>'></asp:TextBox>
                    </EditItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText ="Contact">
                    <ItemTemplate>
                        <%#Eval("ContactName") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox ID="TextBox2" runat="server" Text ='<%#Eval("ContactName") %>'></asp:TextBox>
                    </EditItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText ="Address">
                    <ItemTemplate>
                        <%#Eval("Address") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox ID="TextBox3" runat="server" Text ='<%#Eval("Address") %>'></asp:TextBox>
                    </EditItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText ="City">
                    <ItemTemplate>
                        <%#Eval("City") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:DropDownList ID="DropDownList1" AutoPostBack="true" runat="server">
                        </asp:DropDownList>
                    </EditItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText ="编辑">
                    <ItemTemplate>
                        <asp:Button ID="Button1" runat="server" Text="编辑" CommandName="Edit" />
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:Button ID="Button2" runat="server" Text="修改" CommandName="Update" />&nbsp;
                        <asp:Button ID="Button3" runat="server" Text="取消" CommandName="Cancel" />
                    </EditItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            databind();
        }
    }
    public void databind()
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString());
        SqlCommand cmd = new SqlCommand("SELECT * FROM CUSTOMERS", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        this.GridView1.DataSource = ds.Tables[0];
        this.GridView1.DataKeyNames = new string[] { "CustomerID", "City" };
        this.GridView1.DataBind();
    }
    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        this.GridView1.EditIndex = e.NewEditIndex;
        databind();
    }
    protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        this.GridView1.EditIndex = -1;
        databind();
    }
    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        foreach (TableCell item in e.Row.Cells)
        {
            item.Attributes.Add("style", "border-color:black");
           
        }
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            DropDownList dr = (DropDownList)e.Row.FindControl("DropDownList1");
            if (dr != null)
            {
                SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString());
                SqlCommand cmd = new SqlCommand("Select distinct City  from Customers", con);
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                da.Fill(ds);
                dr.DataSource = ds.Tables[0];
                dr.DataTextField = "City";
                dr.DataValueField = "City";
                dr.DataBind();
                dr.SelectedItem.Text = this.GridView1.DataKeys[e.Row.RowIndex].Values[1].ToString();
            }
        }
    }
    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString());
        SqlCommand cmd = new SqlCommand("Update Customers set CompanyName=@CompanyName,ContactName=@ContactName,City=@City where CustomerID=@CustomerID", con);
        SqlParameter[] ps = new SqlParameter[4];
        ps[0] = new SqlParameter("@CompanyName",SqlDbType.NVarChar,40);
        ps[1] = new SqlParameter("@ContactName",SqlDbType.NVarChar,30);
        ps[2] = new SqlParameter("@City",SqlDbType.NVarChar,15);
        ps[3] = new SqlParameter("@CustomerID",SqlDbType.NChar,5);
        ps[0].Value = ((TextBox)this.GridView1.Rows[e.RowIndex].FindControl("TextBox1")).Text.Trim();
        ps[1].Value = ((TextBox)this.GridView1.Rows[e.RowIndex].FindControl("TextBox2")).Text.Trim();
        ps[2].Value = ((DropDownList)this.GridView1.Rows[e.RowIndex].FindControl("DropDownList1")).SelectedItem.Text;
        ps[3].Value = this.GridView1.DataKeys[e.RowIndex].Values[0];
        cmd.Parameters.AddRange(ps);
        if (con.State == ConnectionState.Closed)
        {
            con.Open();
        }
        cmd.ExecuteNonQuery();
        this.GridView1.EditIndex = -1;
        databind();
    }