dotnet windows forms: I struggled with a problem I had with a combobox bound to a
bindingsource which has as its datasource a collection of custom
objects. The comobobx was bound to a nullable integer property of the
custom object.

When I tried to change the value of the dropdown and tabbed off the
control, the dropdown index would revert back to what it originally
was, so I could not change the value. I placed a breakpoint at the
Leave event of the combobox and single-stepped. It went into the
getter, not the setter!

So I changed the definition of the property in the object bound to the
combobox from Nullable(Of Integer) to Integer and it worked properly.
After the Leave event, it goes into the Setter.

Hi Flomo,

I performed a test based on your description and did see the same thing as
you did.

We could change the value of type Nullable(of Integer) by assigning a value
of type Integer or Nullable(of Integer) to it directly. It seems that the
problem comes from data binding, which in this case doesn't push the new
value to the data source.

I subscribe and handle the Parse event of the Binding object that is added
to the DataBindings property of the ComboBox control, and find that the new
value being pushed to the data source is of type Integer. The following is
the code to subscribe the Parse event of the Binding object and the code of
the event handler.

AddHandler Me.ComboBox1.DataBindings.Item(0).Parse, AddressOf comboboxParse

Private Sub comboboxParse(ByVal sender As Object, ByVal e As
System.Windows.Forms.ConvertEventArgs)
' e.Value is of type Integer.
Dim obj As Object = e.Value
End Sub

In the Parse event handler, e.Value is of type Integer. Apparently, data
binding couldn't update the property of type Nullable(Of Integer) with the
value of Integer.

The workaround is simple, i.e. changing the property value by assigning the
new value to it directly in the Parse event handler. The following is a
sample.

Private Sub comboboxParse(ByVal sender As Object, ByVal e As
System.Windows.Forms.ConvertEventArgs)
' the obj is a variable refereced to the current object in the data
source
obj = e.Value
End Sub

I have performed a test on the above workaround and confirmed it works.

Hope this helps.

If you have any question, please feel free to let me know.


Sincerely,
Linda Liu
Microsoft Online Community Support

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Linda,

Thanks for the reply.

In it you said:

[quoted text, click to view]

I assumed that by obj you meant sender. If the assumption is correct,
it does not fix the problem.

My code is:

Dim bndTypeOffset As Binding =
cboTypeOffset.DataBindings.Add("SelectedValue", CampaignBindingSource,
"CampaignDetail.TypeOffset")
AddHandler bndTypeOffset.Parse, AddressOf ParseTypeOffset

....
Private Sub ParseTypeOffset(ByVal sender As Object, ByVal e As
ConvertEventArgs)
sender = e.Value
End Sub

Thanks for the specifics, Linda.

Is it possible for you to send your entire test code to me? It would
be a great help.

Thanks, Flomo

On Fri, 09 Feb 2007 02:30:10 GMT, v-lliu@online.microsoft.com (Linda
[quoted text, click to view]