Trouble binding a dropdown list in a detailsview.

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G

Guest

Ok, I'm lost. I'm writing a webpage in VB/Dot Net 2.0 and I'm trying to put a
dropdown list in a detailsview. The dropdownlist is supposed to display a
simple enum.

From what little I've seen so far, the place in VB code to bind a ddl is in
the detailview's databound event. Any earlier and you can't get a handle on
the ddl. The detailsview is essentially alone on it's page and is called in
either edit or insert mode only. (In the page lode, I examine a querystring
parameter and based on that, set the detailsview to either edit or insert
mode.) I have created template ddls in the column corresponding to this
variable. All existing records have valid values in this field (a smallint).


The code itself is routine:
ddlClassType = DetailsView1.FindControl("ddlClassType")
Dim names() As String = System.Enum.GetNames(GetType(ClassType))
Dim values() As Integer = System.Enum.GetValues(GetType(ClassType))
Dim i As Integer
For i = 0 To names.Length - 1
Dim item As New ListItem(names(i), values(i).ToString)
ddlClassType.Items.Add(item)
Next

This works fine for Inserts but the code never gets to this point for
updates. It crashes with the error: 'ddlClassType' has a SelectedValue which
is invalid because it does not exist in the list of items. Parameter name:
value

Any suggestions?
 
Howdy,

Moving population code into detail's DataBinding event should resolve the
problem. Take a look at your aspx code and notice, there's Bind or Eval
statement inside SelectedValue: SelectedValue='<%# Eval("WhatEver") %>' which
expects items have already been populated. Unfortunatelly, you're populating
items afterwards, hence the exception.

hope this helps
 
Sorry, actually no. If I move the code into the DetailView's DataBinding
event (or the screen's), the code fails entirely because it can't find the
ddl. Hasn't been rendered yet.

I have a vague memory of populating a dropdown in my last job using
javascript and those <%# %> brackets, but I'm still digging through my notes
for that one. Have you ever done that?
 
Many times. Paste the code.
--
Milosz


B. Chernick said:
Sorry, actually no. If I move the code into the DetailView's DataBinding
event (or the screen's), the code fails entirely because it can't find the
ddl. Hasn't been rendered yet.

I have a vague memory of populating a dropdown in my last job using
javascript and those <%# %> brackets, but I'm still digging through my notes
for that one. Have you ever done that?
Click to expand...
 
Hi

Sorry, actually no. If I move the code into the DetailView's DataBinding
event (or the screen's), the code fails entirely because it can't find the
ddl. Hasn't been rendered yet.
Click to expand...

Milosz is right about the timing of the code causing the exception. In
insert mode, there is no attempt to automatically bind the selected
value of the ddl control to a field value because it's a new record,
whereas in Edit mode it tries to bind the selected value to the
current value of the field.

To get round this you'll have to delete the databinding between the
ddl and the datasource (in the edit mode template) and set the
selected value manually in code immediately after the code you have
already written. In the DataBound event, you can differentiate
betweeen the two modes using DetailsView1.CurrentMode() and make the
code for setting the ddl selected value conditonal upon that.

You'll also need to handle the update manually for the respective
datafield as well in the Updating event.

HTH
 
Thank you Milosz and Phil.

Out of town for the holiday but I continue this as soon as I get home Friday.
 
After some trial and error, I finally got it to work. Is this roughly what
you had in mind? (I first replaced the ddl in the edit template with a new
unbound dropdownlist.)

Private Sub DetailsView1_DataBound(ByVal sender As Object, ByVal e As
System.EventArgs) Handles DetailsView1.DataBound

Dim names() As String = System.Enum.GetNames(GetType(ClassType))
Dim values() As Integer = System.Enum.GetValues(GetType(ClassType))

If DetailsView1.CurrentMode = DetailsViewMode.Edit Then
ddlClassType = DetailsView1.FindControl("ddlClassType")
Dim i As Integer
For i = 0 To names.Length - 1
Dim item As New ListItem(names(i), values(i).ToString)
ddlClassType.Items.Add(item)
Next

' Set incoming value
Dim dr As DataRowView
dr = DetailsView1.DataItem
ddlClassType.SelectedValue = dr.Item("ClassType").ToString
End If

End Sub

Private Sub ObjectDataSource1_Updating(ByVal sender As Object, ByVal e
As System.Web.UI.WebControls.ObjectDataSourceMethodEventArgs) Handles
ObjectDataSource1.Updating
' manually update values here
ddlClassType = DetailsView1.FindControl("ddlClassType")
e.InputParameters.Item("ClassType") = ddlClassType.SelectedValue
End Sub
 
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