C# 从下拉列表中动态填充文本框不工作

我试图在下拉列表中选择其值时填充两个文本框（我希望文本框中的数据在选择更改而不重新加载页面时更改），我编写了一些代码编译从其他类似问题中收集到的内容，但出于某种原因，我的CS在这里不起作用

public partial class UsersFormPage : Page
{
    protected void userddlistedit_SelectedIndexChanged(object sender, EventArgs e)
    {
        FillBoxes(userddlistedit.SelectedValue);
    }

    private void FillBoxes(string HR_ID)
    {
        // Create a new dataset object
        DataSet dt = new DataSet();
        // Create SqlConnection
        using (SqlConnection conn = new SqlConnection())
        {
            conn.ConnectionString = "Data Source=SQL2008R2SRV;Initial Catalog=employeetrainingtracking;Integrated Security=True";
            conn.Open();
            using (SqlCommand cmd = new SqlCommand())
            {
                // Set the connection on the sql command object
                cmd.Connection = conn;
                cmd.CommandText = "select * from users where HR_ID='" + HR_ID + "'";
                using (SqlDataAdapter adap = new SqlDataAdapter(cmd))
                {
                    adap.Fill(dt);
                }
            }
        }
        if (dt.Tables[0].Rows.Count > 0)
        {
            usernameedit.Text = dt.Tables[0].Rows[0]["Username"].ToString(); //Where column name us the Fields for your Table that you wanted to display in the TextBoxes
            passwordedit.Text = dt.Tables[0].Rows[0]["Password"].ToString();
        }
    }
}

以下是我的页面影响的部分：

  <li class="form-row text-row">
    <label>User:</label>
      <asp:DropDownList ID="userddlistedit" runat="server" CssClass="text-input-dds" DataSourceID="personnelsql" DataTextField="HR_ID" DataValueField="HR_ID" AutoPostBack="True" OnSelectedIndexChanged="userddlistedit_SelectedIndexChanged" />
  </li>
  <li class="form-row text-input-row">
    <label>Username:</label>
    <asp:TextBox name="usernameedit" type="text" class="text-input-lg required" id="usernameedit" runat="server" AutoPostBack="True" />                     
  </li>
  <li class="form-row text-input-row">
    <label>Password:</label>
    <asp:TextBox name="passwordedit" type="text" class="text-input-lg required" id="passwordedit" runat="server" AutoPostBack="True" />
  </li>

用户：


用户名：


密码：

我似乎不明白为什么它不起作用

这是我的下拉列表的数据源：

                      <asp:SqlDataSource ID="personnelsql" runat="server" 
                      ConnectionString="<%$ ConnectionStrings:employeetrainingtrackingConnectionString %>" 
                      SelectCommand="SELECT * FROM personnel ORDER BY HR_ID">
                  </asp:SqlDataSource>

---

我找出了我遗漏的内容，因此我将代码发布在下面，以便人们可以使用它：

以下是CS页面上的代码：

protected void userddlistedit_SelectedIndexChanged(object sender, EventArgs e)
{
    string selectSQL;
    selectSQL = "SELECT * FROM users ";
    selectSQL += "WHERE HR_ID='" + userddlistedit.SelectedItem.Value + "'";
    SqlConnection con = new SqlConnection(connectionString);
    SqlCommand cmd = new SqlCommand(selectSQL, con);
    SqlDataReader reader;

    try
    {
        con.Open();
        reader = cmd.ExecuteReader();
        reader.Read();

        usernameedit.Text = reader["Username"].ToString();
        passwordedit.Text = reader["Password"].ToString();
        accessleveledit.SelectedValue = reader["AccessLevel"].ToString();
        reader.Close();
        lblResults.Text = "";
    }
    finally
    {
        con.Close();
    }
}

private void UsersListDD()
{
    userddlist.Items.Clear();
    userddlistedit.Items.Clear();
    userddlistdelete.Items.Clear();
    string selectSQL = "SELECT * FROM personnel";

    SqlConnection con = new SqlConnection(connectionString);
    SqlCommand cmd = new SqlCommand(selectSQL, con);
    SqlDataReader reader;

    try
    {
        con.Open();
        reader = cmd.ExecuteReader();
        while (reader.Read())
        {
            ListItem newItem = new ListItem();
            newItem.Text = reader["FirstName"] + " " + reader["LastName"];
            newItem.Value = reader["HR_ID"].ToString();
            userddlist.Items.Add(newItem);
            userddlistedit.Items.Add(newItem);
            userddlistdelete.Items.Add(newItem);
        }
        reader.Close();
    }
    finally
    {
        con.Close();
    }
}

这是实际aspx页面中的代码，我添加了两件事： -我添加了DropDownExtender -我添加了触发器（在标记之后但在标记之前）

<li class="form-row text-row">
                <label>User:</label>
                  <asp:DropDownList ID="userddlistedit" runat="server" CssClass="text-input-dds" AutoPostBack="True" OnSelectedIndexChanged="userddlistedit_SelectedIndexChanged"></asp:DropDownList>
              </li>
              <li class="form-row text-input-row">
                <label>Username:</label>
                <asp:TextBox name="usernameedit" type="text" class="text-input-lg required" id="usernameedit" runat="server"></asp:TextBox>
                <asp:DropDownExtender ID="ExtenderUserEdit" DropDownControlID="userddlistedit" Enabled="true" TargetControlID="usernameedit" runat="server"></asp:DropDownExtender>
                <asp:RequiredFieldValidator runat="server" ID="ValidateUsernameEdit" ControlToValidate="usernameedit" ErrorMessage="Username is required" Display="dynamic" ValidationGroup="EditSection">*</asp:RequiredFieldValidator>
              </li>
              <li class="form-row text-input-row">
                <label>Password:</label>
                <asp:TextBox name="passwordedit" type="text" class="text-input-lg required" id="passwordedit" runat="server"></asp:TextBox>
                <asp:RequiredFieldValidator runat="server" ID="ValidatePasswordEdit" ControlToValidate="passwordedit" ErrorMessage="Password is required" Display="dynamic" ValidationGroup="EditSection">*</asp:RequiredFieldValidator>
              </li>  

---

希望这对其他人有所帮助。

在填充下拉列表的地方，您的页面加载为空？？？您好。感谢您的帮助。我编辑了我的问题，为我的下拉列表添加了数据源。这就是您所指的吗？您是否已通过输入break进行了检查？正在运行以填充控件的代码已在serve中完成因此，为了重新绑定页面控件，您不可避免地必须回发到服务器。如果您想要这种类型的功能，则必须在客户端完成（使用Javascript/JQuery），但即使如此，您的应用程序也必须运行服务器端代码才能从数据库中获取数据。同样重要的是，要记住，任何回服务器的帖子都会导致页面再次加载，您必须注意正确地重新绑定控件。因此，从您的vie角度来看，这段代码是否很好，但它需要一个javascript函数来升级吃了这一页？

private void UsersListDD()
{
    userddlist.Items.Clear();
    userddlistedit.Items.Clear();
    userddlistdelete.Items.Clear();
    string selectSQL = "SELECT * FROM personnel";

    SqlConnection con = new SqlConnection(connectionString);
    SqlCommand cmd = new SqlCommand(selectSQL, con);
    SqlDataReader reader;

    try
    {
        con.Open();
        reader = cmd.ExecuteReader();
        while (reader.Read())
        {
            ListItem newItem = new ListItem();
            newItem.Text = reader["FirstName"] + " " + reader["LastName"];
            newItem.Value = reader["HR_ID"].ToString();
            userddlist.Items.Add(newItem);
            userddlistedit.Items.Add(newItem);
            userddlistdelete.Items.Add(newItem);
        }
        reader.Close();
    }
    finally
    {
        con.Close();
    }
}