C# 在下拉列表中获取所选值的ID

我试图在数据库中保存数据，作为其中的一部分，我试图在下拉列表中获取所选项目的ID（主键）

它一直保存相同的ID。它只保存任何选定项目的第一个ID。如何调整代码，使其根据我在下拉列表中选择的内容保存不同的ID

protected void Page_Load(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection(
    WebConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString);
    con.Open();
    SqlCommand cmd = new SqlCommand("Select UserRoleID, RoleType from tb_UserRoles", con);
    DropDownList1.DataSource = cmd.ExecuteReader();
    DropDownList1.DataTextField = "RoleType";
    DropDownList1.DataValueField = "UserRoleID";
    DropDownList1.DataBind();
}

protected void Button1_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection(
    WebConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString);
    con.Open();
    SqlCommand cmd = new SqlCommand("sp_UserInsertUpdate", con);
    cmd.CommandType = System.Data.CommandType.StoredProcedure;
    String ID = DropDownList1.SelectedValue;
    cmd.Parameters.AddWithValue("UserID", (hfUserID.Value == "" ? 0 : Convert.ToInt32(hfUserID.Value)));
    cmd.Parameters.AddWithValue("UserRoleID", ID);
    cmd.Parameters.AddWithValue("Username", TextBox1.Text);
    cmd.Parameters.AddWithValue("Password", TextBox2.Text);
    cmd.Parameters.AddWithValue("Email", TextBox3.Text);
    cmd.Parameters.AddWithValue("DateCreate", TextBox4.Text);
    cmd.ExecuteNonQuery();
    con.Close();
}

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这是因为每次你点击按钮。click事件发生，但在此之前它执行页面加载事件，在页面加载事件中，您添加了绑定逻辑下拉列表。这意味着无论何时单击按钮，每次它首次加载下拉列表时，都会出现单击事件。为此，您只需使用

IsPostBack

添加一个if条件

进行如下更改

protected void Page_Load(object sender, EventArgs e)
{
   if(!IsPostBack) //Added
   {
     SqlConnection con = new SqlConnection(
     WebConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString);
     con.Open();
     SqlCommand cmd = new SqlCommand("Select UserRoleID, RoleType from tb_UserRoles", con);
     DropDownList1.DataSource = cmd.ExecuteReader();
     DropDownList1.DataTextField = "RoleType";
     DropDownList1.DataValueField = "UserRoleID";
     DropDownList1.DataBind();
  }
}

---

你应该检查

！iPostBack

protected void Page_Load(object sender, EventArgs e)
{
    if(!IsPostBack) // Add this If condition
    {
        SqlConnection con = new SqlConnection(
        WebConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString);
        con.Open();
        SqlCommand cmd = new SqlCommand("Select UserRoleID, RoleType from tb_UserRoles", con);
        DropDownList1.DataSource = cmd.ExecuteReader();
        DropDownList1.DataTextField = "RoleType";
        DropDownList1.DataValueField = "UserRoleID";
        DropDownList1.DataBind();
    }
}
protected void Button1_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection(
    WebConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString);
    con.Open();
    SqlCommand cmd = new SqlCommand("sp_UserInsertUpdate", con);
    cmd.CommandType = System.Data.CommandType.StoredProcedure;
    String ID = DropDownList1.SelectedValue;
    cmd.Parameters.AddWithValue("UserID", (hfUserID.Value == "" ? 0 : Convert.ToInt32(hfUserID.Value)));
    cmd.Parameters.AddWithValue("UserRoleID", ID);
    cmd.Parameters.AddWithValue("Username", TextBox1.Text);
    cmd.Parameters.AddWithValue("Password", TextBox2.Text);
    cmd.Parameters.AddWithValue("Email", TextBox3.Text);
    cmd.Parameters.AddWithValue("DateCreate", TextBox4.Text);
    cmd.ExecuteNonQuery();
    con.Close();
}

---

请不要剽窃内容。