[Solved] ASP.Net DropDownList SelectedValue returning NULL when using SqlDataSource

tanweeru...

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User: tanweeruddinbeeharry
Posted: on Dec 16, 2021 06:34 AM
Forum: ASP.Net Web Forms
Answer: 1
Views: 5686
Sample Code: Download

on page load i am calling this code below. Unable to get the selectedvalue i am getting null for each string.

 String T_id = ddlTeacherDetails.SelectedValue;
 String g_id = ddlgrade.SelectedValue;
 String s_id = ddlsubject.SelectedValue;
 getNumberofpostedresTeacher(T_id, g_id, s_id);

<div class="row"> 
    <div class="col-md-3">
        <asp:DropDownList ID="ddlgrade" runat="server" DataSourceID="SqlDataSourceBindddlgrade" CssClass="form-control" DataTextField="grade_name" DataValueField="grade_id"></asp:DropDownList>
    </div>
    <div class="col-md-3">
        <asp:DropDownList ID="ddlsubject" runat="server" DataSourceID="SqlDataSourceBindddlsubject" CssClass="form-control" DataTextField="subject_name" DataValueField="subject_id"></asp:DropDownList>
    </div>
    <div class="col-md-3">
        <asp:DropDownList ID="ddlTeacherDetails" runat="server" DataSourceID="SqlDataSourceBindteacherDDL" CssClass="form-control" DataTextField="teachername" DataValueField="teacher_id"></asp:DropDownList>
    </div>
    <div class="col-md-3">
        <asp:Button runat="server" ID="btnshow" Text="Show" CssClass="btn btn-info" OnClick="btnshow_Click" />
    </div>
</div>
<asp:SqlDataSource ID="SqlDataSourceBindteacherDDL" runat="server" ConnectionString="<%$ ConnectionStrings:maudigitalstore %>" SelectCommandType="Text" SelectCommand="SELECT t.teacher_id, t.tch_F_name + ' ' + t.tch_L_name as teachername FROM tblteacher t" />
<asp:SqlDataSource ID="SqlDataSourceBindddlgrade" runat="server" ConnectionString="<%$ ConnectionStrings:maudigitalstore %>" SelectCommandType="Text" SelectCommand="SELECT t.grade_id, t.grade_name FROM tblgrade t " />
<asp:SqlDataSource ID="SqlDataSourceBindddlsubject" runat="server" ConnectionString="<%$ ConnectionStrings:maudigitalstore %>" SelectCommandType="Text" SelectCommand="SELECT t.subject_id, t.subject_name FROM tblsubject t " />

dharmend...

0 6

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ANSWER
User: dharmendr
Replied: on Dec 17, 2021 03:34 AM
Modified: on Feb 24, 2022 09:08 AM
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Hi tanweeruddinb...,

You need to call the DropDownList DataBind method before accessing the selected item.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

<asp:DropDownList ID="ddlEmployees" runat="server" DataSourceID="SqlDataSourceEmployees" 
    DataTextField="FirstName" DataValueField="EmployeeID"></asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSourceEmployees" runat="server" ConnectionString="<%$ ConnectionStrings:conString %>" 
    SelectCommand="SELECT [EmployeeID], [FirstName] FROM [Employees]"></asp:SqlDataSource>
<asp:DropDownList ID="ddlCountries" runat="server" DataSourceID="SqlDataSourceCountries" 
    DataTextField="Country" DataValueField="EmployeeID"></asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSourceCountries" runat="server" ConnectionString="<%$ ConnectionStrings:conString %>" 
    SelectCommand="SELECT [EmployeeID], [Country] FROM [Employees]"></asp:SqlDataSource>

Code

protected void Page_Load(object sender, EventArgs e)
{
    this.ddlEmployees.DataBind();
    string empId = ddlEmployees.SelectedValue;
    this.ddlCountries.DataBind();
    string country = ddlCountries.SelectedItem.Text;
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Employee Id : " + empId + "\\nCountry: " + country + "');", true);
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Me.ddlEmployees.DataBind()
    Dim empId As String = ddlEmployees.SelectedValue
    Me.ddlCountries.DataBind()
    Dim country As String = ddlCountries.SelectedItem.Text
    ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Employee Id : " & empId & "\nCountry: " & country & "');", True)
End Sub

Screenshot

[Solved] ASP.Net DropDownList SelectedValue returning NULL when using SqlDataSource

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