ComboBox Events

Since I couldn't find this information anywhere else...

For a ComboBox with the following settings, the order of events is as follows:

Settings
AutoCompleteMode----------Suggest
AutoCompleteSource--------ListItems
DataSource-------------------System.Windows.Forms.BindingSource
DisplayMember--------------[Database field]
DropDownStyle--------------DropDownList
ValueMember----------------[Database field]

Others as default

Form Load
1. DisplayMemberChanged
2. ValueMemberChanged
3. SelectedValueChanged
4. SelectedValueChanged
5. SelectedValueChanged
6. SelectedValueChanged (repeats four times)

Click on Control (gets focus)
1. Enter
[dropped down list then appears]

Choose a List Item with Mouse Click
[dropped down list retracts]
1. TextChanged
2. SelectionChangeCommitted
3. SelectedValueChanged
4. SelectedIndexChanged

Change the List Item with the Mouse Scroll Wheel
1. SelectionChangeCommitted
2. SelectedValueChanged
3. SelecetdIndexChanged

Note: The TextChanged event does not fire with the scroll wheel as it does via mouse clicks on the dropped down list

Exit Control (loses focus)
1. Leave
2. Validating
3. Validated

Form Close
1. TextChanged
2. SelectedValueChanged
3. SelectedIndexChanged
4. DisplayMemberChanged


Qualifying Comments
I did not test all events, only those I thought might fire (and where relevant to my issue) during form load, user interaction and form close. Therefore I tested the following:

DisplayMemberChanged
Enter
Leave
SelectedIndexChanged
SelectedValueChanged
SelectionChangeCommitted
TextChanged
TextUpdate
Validated
Validating
ValueMemberChanged

Therefore other events might have been firing but I was not handling them in my testing.


My reason for the testing was that the ComboBox selection needed to cause a 2nd ComboBox to be filtered (BindingSource.Filter property) and it caused an exception on Form Close* and didn't work with the scroll wheel. It would also have been useful if the 2nd ComboBox would filter correctly on Form Load based on the default value of the ComboBox I was handling.

Analysis of the above led me to use SelectionChangeCommitted since it fired when the user selected a value via mouse clicks or via the scroll wheel but did not fire on Form Close. I could not see an option that also fired during Form load (but not in Form Close, since avoiding the exception was higher priority) so I added the same line of filtering code that is in the SelectionChangeCommitted handler to the Form Load handler.

Private Sub cmbRegion_SelectionChangeCommitted(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbRegion.SelectionChangeCommitted
    Me.Countries_BindingSource.Filter = "[region_id] = '" & Me.cmbRegion.SelectedValue.ToString & "'"
End Sub

* I believe the NullReferenceException was being caused during Form Close due to the BindingSource component for the 2nd ComboBox being destroyed before the ComboBox I was handling and hence using the TextChanged event I would be trying to refer to a BindingSource that had been destroyed, but I can't be sure.