Databinding with combobox not working

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Flomo Togba Kwele - 06 Apr 2007 02:59 GMT

I have defined a custom class and used it in a generic BindingList as the
datasource of a BindingSource.

I bound a combobox like on the form as:
cboFirstClass.DataBindings.Add("SelectedValue", bsClient, "FirstClass", True)

When a new custom object is created, I initialize the combobox as follows:
If cboFirstClass.Items.Count > 0 Then
cboFirstClass.SelectedIndex = 0
End If

which displays the first entry in the list. The combobox is loaded with a
List(Of String).

If I do not select a member from the combobox (that is, I leave it as the
default above), it does not bind to the custom object's property (FirstClass) -
it leaves it blank. If I do change the selection of the combobox, even putting
it back to the original default value, it then binds to the custom object's
property.

If I use Text instead of SelectedValue to bind the combobox to the custom
object's property, it binds OK whether or not I make a selection from the
combobox. But it does not display anything in the combobox - the user must make
a selection.

What is the proper way to databind to a combobox? Is this behavior with
SelectedValue normal when no selection of the combobox has been made?

Thanks, Flomo

--

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Linda Liu [MSFT] - 06 Apr 2007 08:33 GMT

Hi Flomo,

Firstly, since you set the ComboBox's DataSource property to a List(Of
String), you should bind the "SelectedItem" or "Text" property of the
ComboBox to a field of another data source. For example:

cboFirstClass.DataBindings.Add("SelectedItem", bsClient, "FirstClass", True)
Or
cboFirstClass.DataBindings.Add("Text", bsClient, "FirstClass", True)

On the other hand, if you set the ComboBox's DataSource property to a data
source as well as specify its ValueMember and DisplayMember properties, you
should bind the ComboBox's "SelectedValue" property to a field of another
data source.

Secondly, if you call the AddNew method of the BindingSource to add a new
object in the data source, the new object should already be bound to the
ComboBox.

If the FirstClass property of your custom class has no default value, the
ComboBox will display nothing when you add a new object in the
BindingSource.

If you'd like the ComboBox to display a default text when you add a new
object in the BindingSource, you could specify a default value for the
FirstClass property in the custom class.

Hope this helps.
If you have anything unclear, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

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Databinding with combobox not working

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