Question

I am trying to use datasource and bind in my application to set a dropdown list to the results of a query. The dropdownlist populates correctly (shows each different type_name in the set) but later when I use ddltype.selectedvalue – I am always getting the value from the first item in the dataset. Here is the code.

        if ds.hasRows = true
        ddlType.DataValueField = "type_id"
        ddlType.DataTextField = "type_name"
        ddlType.DataSource = ds
        ddlType.DataBind()
        end if

Then later on I use the following code to try to get teh selected value

        Dim typeID = ddlType.SelectedValue

I have ran the query to get the dataset on my SQL server and get the below results – but every time I use the above dim statement, the value is set to 812 even when type 2 is selected. Below is the results from the query that fills the sqldatareader named ds.

type_id : type_name
___________________
812     : type one

813     : type two

Thanks in advance.

Answer 1

Based on the information in your question, I don’t see anything wrong.

But based on common mistakes people make with this pattern, I am guessing you are probably running ddlType.DataBind() on every postback. So the user clicks a button or something similar to fire the postback, and the DDL is re-bound before your click handler checks the value. Re-binding sets the selectedvalue back to default.

Edit: Your databinding code in Page_Load should only run once. One way to do this is to wrap the databinding code…

    If Not IsPostBack Then
        If ds.hasRows = True Then
            ddlType.DataValueField = "type_id"
            ddlType.DataTextField = "type_name"
            ddlType.DataSource = ds
            ddlType.DataBind()
        End If
    End If

This will cause the databinding to occur only the first time the page is requested, but not after a button click or other postback action.