教室水平] WHERE [教室类别] ='{0}'， NURSERY）;
BindDropDownList（ this .ddlAppClass，query， 描述， 教室类别， ---选择---）;
}

}

绑定方法：

  private   void  BindDropDownList（DropDownList） ddl，字符串查询，字符串文本，字符串 值， string  defaultText）
 {
 string  conString = ConfigurationManager.ConnectionStrings [  DatabaseDemo数据库NAV（8-0）1]。ConnectionString; 
 SqlCommand cmd =  new  SqlCommand（query）; 
使用（SqlConnection con =  new  SqlConnection（conString））
 {
使用（SqlDataAdapter sda =  new  SqlDataAdapter（））
 {
 cmd .Connection = con; 
 con.Open（）; 
 ddl.DataSource = cmd.ExecuteReader（）; 
 ddl.DataTextField = text; 
 ddl.DataValueField =  value ; 
 ddl.DataBind（）; 
 con.Close（）; 
} 
} 
 ddl.Items.Insert（ 0 ， new  ListItem（defaultText，  0））; 
} 

我的DropdownList源代码：



< asp：DropDownList ID = ddlAppClass runat = server AutoPostBack = True 高度 = 20px 宽度 = 188px OnSelectedIndexChanged = ddlAppClass_SelectedIndexChanged EnableViewState = true > < / asp：DropDownList >

阅读价值：

 如果（ this  .ddlAppClass.SelectedIndex！=  0 ）
 {
 SchoolAge（ this 跨度> .ddlAppClass.SelectedItem.Text）; 
} 

SchoolAge方法：

 private void SchoolAge（string _classType）
 {
 try 
 {
 var select =SELECT [ClassType]，[age] FROM [Corona Schools_ Trust Council 

AddAge] WHERE [ClassType] = @ClassType;
SqlDataReader rder = null;
using（var connection = new SqlConnection（ConfigurationManager.ConnectionStrings [DatabaseDemo Database NAV（8-0）1]。ConnectionString））
{
using（var command = new SqlCommand（select） ，connection））
{
command.CommandType = CommandType.Text;
command.Parameters.Add（@ ClassType，SqlDbType.VarChar，50）.Value = _classType;
connection.Open（）;
rder = command.ExecuteReader（）;
while（rder.Read（））
{

ValidateAge.Text =（rder [age]。ToString（））;

}

}
}
}
catch（SqlException ex）
{
// lblMsg。 Text = ex.Message;
//lblMsg.ForeColor = System.Drawing.Color.Red;
}

}

感谢您的协助！

 <   asp：DropDownList     ID   =  ddlAppClass    runat   =  server    AutoPostBack   =  True   高度  =  20px   宽度  =  188px    OnSelectedIndexChanged   =  ddlAppClass_SelectedIndexChanged    EnableViewState   =  true >  <   / asp：DropDownList  >  

<   asp：TextBox     ID   =  txtDateOfBirth     OnTextChanged   =  txtDateOfBirth_TextChan ged    AutoPostBack   =  true    runat   =  server    /  >  

所选项目：<   asp：Literal     ID   =  LiteralResult    runat   =  server    /  >  

代码隐藏

 受保护  void  Page_Load（ object  sender，EventArgs e）
 {
 if （！Page.IsPostBack）
 {
 string  query =  string  .Format（  SELECT [教室类别]，[描述] FROM [Corona Schools_ Trust Council 

Hello Everyone,

i have an issue i have been battling with for sometime now, my dynamic DropDownList always return to the first item from database, i have done a few researches on how to resolve this including enabling Viewstate for the page and DropDownList and placing the code on if(!Page.IsPostback) but the issue persists!

Here is my code:

What I have tried:

if (!Page.IsPostBack)
                {
                    string appType2 = Session["applicationType"].ToString();
                    if (appType2 == "nur")
                    {

                        FetchApplicationFeeFromDB("NURSERY");
                        this.ddlAppClass.Items.Clear();
                        this.ddlApplicationType.Items.Insert(0, "NURSERY SCHOOL");

                        string query = string.Format("SELECT [Teaching Room Category] ,[Description] FROM [Corona Schools_ Trust Council$Teaching Room Level] WHERE [Teaching Room Category] = '{0}'", "NURSERY");
                        BindDropDownList(this.ddlAppClass, query, "Description", "Teaching Room Category", "---Select---");
                    }

                }

Binding Method:

private void BindDropDownList(DropDownList ddl, string query, string text, string value, string defaultText)
    {
        string conString = ConfigurationManager.ConnectionStrings["DatabaseDemo Database NAV (8-0)1"].ConnectionString;
        SqlCommand cmd = new SqlCommand(query);
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                con.Open();
                ddl.DataSource = cmd.ExecuteReader();
                ddl.DataTextField = text;
                ddl.DataValueField = value;
                ddl.DataBind();
                con.Close();
            }
        }
        ddl.Items.Insert(0, new ListItem(defaultText, "0"));
    }

My DropdownList Source code:

<asp:DropDownList ID="ddlAppClass" runat="server" AutoPostBack="True" Height="20px" Width="188px" OnSelectedIndexChanged="ddlAppClass_SelectedIndexChanged" EnableViewState="true"></asp:DropDownList>

Reading Value:

if (this.ddlAppClass.SelectedIndex != 0)
                {
                    SchoolAge(this.ddlAppClass.SelectedItem.Text);                    
                }

SchoolAge Method:

private void SchoolAge(string _classType)
        {
            try
            {
                var select = "SELECT [ClassType],[age] FROM [Corona Schools_ Trust Council$AddAge] WHERE [ClassType] = @ClassType";
                SqlDataReader rder = null;
                using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DatabaseDemo Database NAV (8-0)1"].ConnectionString))
                {
                    using (var command = new SqlCommand(select, connection))
                    {
                        command.CommandType = CommandType.Text;
                        command.Parameters.Add("@ClassType", SqlDbType.VarChar, 50).Value = _classType;
                        connection.Open();
                        rder = command.ExecuteReader();
                        while (rder.Read())
                        {

                            ValidateAge.Text = (rder["age"].ToString());

                        }

                    }
                }
            }
            catch (SqlException ex)
            {
                //lblMsg.Text = ex.Message;
                //lblMsg.ForeColor = System.Drawing.Color.Red;
            }

        }

I appreciate your assistance!

Teaching Room Level] WHERE [Teaching Room Category] = '{0}'", "NURSERY"); BindDropDownList(this.ddlAppClass, query, "Description", "Teaching Room Category", "---Select---"); } }

Binding Method:

private void BindDropDownList(DropDownList ddl, string query, string text, string value, string defaultText)
    {
        string conString = ConfigurationManager.ConnectionStrings["DatabaseDemo Database NAV (8-0)1"].ConnectionString;
        SqlCommand cmd = new SqlCommand(query);
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                con.Open();
                ddl.DataSource = cmd.ExecuteReader();
                ddl.DataTextField = text;
                ddl.DataValueField = value;
                ddl.DataBind();
                con.Close();
            }
        }
        ddl.Items.Insert(0, new ListItem(defaultText, "0"));
    }

My DropdownList Source code:

<asp:DropDownList ID="ddlAppClass" runat="server" AutoPostBack="True" Height="20px" Width="188px" OnSelectedIndexChanged="ddlAppClass_SelectedIndexChanged" EnableViewState="true"></asp:DropDownList>

Reading Value:

if (this.ddlAppClass.SelectedIndex != 0)
                {
                    SchoolAge(this.ddlAppClass.SelectedItem.Text);                    
                }

SchoolAge Method:

private void SchoolAge(string _classType)
        {
            try
            {
                var select = "SELECT [ClassType],[age] FROM [Corona Schools_ Trust Council

AddAge] WHERE [ClassType] = @ClassType"; SqlDataReader rder = null; using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DatabaseDemo Database NAV (8-0)1"].ConnectionString)) { using (var command = new SqlCommand(select, connection)) { command.CommandType = CommandType.Text; command.Parameters.Add("@ClassType", SqlDbType.VarChar, 50).Value = _classType; connection.Open(); rder = command.ExecuteReader(); while (rder.Read()) { ValidateAge.Text = (rder["age"].ToString()); } } } } catch (SqlException ex) { //lblMsg.Text = ex.Message; //lblMsg.ForeColor = System.Drawing.Color.Red; } }

I appreciate your assistance!

<asp:DropDownList ID="ddlAppClass" runat="server" AutoPostBack="True" Height="20px" Width="188px" OnSelectedIndexChanged="ddlAppClass_SelectedIndexChanged" EnableViewState="true"></asp:DropDownList>

<asp:TextBox ID="txtDateOfBirth" OnTextChanged="txtDateOfBirth_TextChanged" AutoPostBack="true" runat="server" />

Selected item: <asp:Literal ID="LiteralResult" runat="server" />

code-behind

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        string query = string.Format("SELECT [Teaching Room Category] ,[Description] FROM [Corona Schools_ Trust Council