SelectIndex_changed在Asp.net中没有用于选择值

Question

我是.net开发的新手我现在面临的问题，但我不知道这个解决方案是什么我创建下拉列表并将其与数据绑定但是当我从列表中选择任何数据时它不会更改文本框相关的值，但当我点击按钮它进入代码意味着继续从我标记调试光标的地方这里是我的代码背后

  protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string selectedCardCode = DropDownList1.SelectedItem.Value;

                 SqlConnection connection = new SqlConnection("Data Source=testing;Initial Catalog=testdb;Persist Security Info=True;User ID=abcd;Password=asdfg");
            using (connection)
            {
                SqlCommand theCommand = new SqlCommand("SELECT T1.CardCode , T1.CardName,T3.CntctCode,T3.Name  FROM OCRD T1 inner join OCPR T3 on T1.CardCode=T3.CardCode where T3.CardCode=@CardCode ", connection);
                connection.Open();
                theCommand.Parameters.AddWithValue("@CardCode", selectedCardCode);
                theCommand.CommandType = CommandType.Text;

                SqlDataReader theReader = theCommand.ExecuteReader();

                if (theReader.Read())
                {
                    this.TextBox1.Text = theReader["CardCode"].ToString();
                    this.TextBox2.Text = theReader["CardName"].ToString();
                    this.DropDownList1.SelectedItem.Value = selectedCardCode;

                        }
                connection.Close();
            }

        }

这是我的方法cardcode

 protected void LoadOptionsCardCodeTable()
        {
            DataTable CardCode = new DataTable();
            string id, name, newName;
            SqlConnection connection = new SqlConnection("Data Source=abc;Initial Catalog=TestDataBase;Persist Security Info=True;User ID=asdf;Password=asdfgh");
            using (connection)
            {
                SqlDataAdapter adapter = new SqlDataAdapter("SELECT T1.CardCode , T1.CardName from ocrd T1 ", connection);
                adapter.Fill(CardCode);

                if (CardCode.Rows.Count > 0)
                {
                    for (int i = 0; i < CardCode.Rows.Count; i++)
                    {

                        id = CardCode.Rows[i]["CardCode"].ToString();
                        name = CardCode.Rows[i]["CardName"].ToString();
                        newName = name + " ---- " + id;

                        DropDownList1.Items.Add(new ListItem(newName, id));
                    }
                }

            }
        }

这是我的设计代码

 <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="DropDownList1" runat="server" 
            ondatabinding="DropDownList1_SelectedIndexChanged" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged">
        </asp:DropDownList>
        <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
    </div>
    <asp:TextBox ID="TextBox1" runat="server" ontextchanged="TextBox1_TextChanged"></asp:TextBox>
    <asp:TextBox ID="TextBox2" runat="server" ontextchanged="TextBox2_TextChanged"></asp:TextBox>
    </form>

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Answer 1

将下拉列表的AutoPostBack属性设置为true。

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" 
      ondatabinding="DropDownList1_SelectedIndexChanged" 
       onselectedindexchanged="DropDownList1_SelectedIndexChanged">
</asp:DropDownList>

默认情况下，asp.net服务器控件如dropdownlist，textbox将各自的事件作为缓存 ，这意味着它会注册事件但不会触发，直到发生实际的回发 。 在您点击按钮的情况下，回发正在发生，并且您的dropdwonlist的缓存事件也将被执行。

要从您的下拉列表强制回发，您必须将PostBack属性设置为true 。

Answer 2

您必须设置AutoPostBack="true"才能触发事件：

 <asp:DropDownList ID="DropDownList1" runat="server" 
            ondatabinding="DropDownList1_SelectedIndexChanged" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged" AutoPostBack="true">
        </asp:DropDownList>

笔记：

浏览器启动回发，并根据事件重新加载整个页面。如果我们在回发中的控件结果中做出任何更改（此处onselectedindexchanged ），那么称为AutoPostBack.All控件除了Buttons ， Hyperlinks和LinkButtons如果默认的AutoPostBack属性为false，我们可以选择在需要时将它们设置为true。

Answer 3

设置AutoPostBack="true"否则DropDownList1_SelectedIndexChanged不会触发。

        <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" 
            ondatabinding="DropDownList1_SelectedIndexChanged" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged">
         </asp:DropDownList>