Error in read data from ASP.NET drop down list

Question

I am changing a code that was written in VB using .net framework 3.5. In here I have to bind some data from the database to a drop down list and then read the selected value. The code for binding data and reading data are as follows.

Public Sub setDropdown_test()
    Dim ds As New DataSet
    Dim dr As DataRow

    Try
        ds = Subject_Test.getSubjectDetails()

        dr = ds.Tables(0).NewRow()
        dr("SBJ_NAME") = "Select the subject"
        dr("SBJ_CODE") = "-1"
        ds.Tables(0).Rows.InsertAt(dr, 0)

        If ds.Tables(0).Rows.Count > 0 Then
            testDrop.DataTextField = ds.Tables(0).Columns("subject_name").Caption
            testDrop.DataValueField = ds.Tables(0).Columns("subject_code").Caption
            testDrop.DataSource = ds
            testDrop.DataBind()
        End If
    Catch ex As Exception
        'write an error here
    End Try
End Sub

Protected Sub testButton_Click(sender As Object, e As EventArgs) Handles testButton.Click
    PoupMessage("selected value is - " & testDrop.SelectedValue & " selected text is - " & testDrop.SelectedItem.ToString())
End Sub

in page Load method setDropdown_test() is called.

Data binding to drop down list is working properly. But every time I select a value and click the testButton the page reloads itself and gives the out put of first column of the drop down list. As far as I know, stop reloading the page is the best way to work this properly. but I failed to do that.
Can someone please help me to solve this.

Aethan · Accepted Answer · 2016-03-10 06:52:17Z

1

It's resetting to the Dropdown's first item because of PostBack, which means in every click of your button, the form do a PostBack and reloads the form, calling the setDropdown_test() again, resetting the value to the first Item in the list.

Cover it with this statement to avoid reloading the DropDownList every PostBack.

If Not IsPostBack Then
     setDropdown_test()
End If

edited Mar 10, 2016 at 6:52

answered Mar 10, 2016 at 6:42

Aethan

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Aethan Over a year ago

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