Hi all,

I'm stumped and have spent many hours puzzling over this.  I have two related comboxboxes, cboClient and cboCoverage on an EventBO maintenance form.   Each is bound to an FK on the EventBO record (CLI_ID and COV_ID). 

When the user selects a new Client, I want the cboCoverage to requery showing only the coverages for this particular client and I want to set its selected value in code to a particular one of the coverage choices.  The logic for this doesn't matter here (I am actually setting the recommended coverage for that client based on several other variables...); here is an ultra simplified version setting a fixed value in code just for demo:

 Private Sub cboClient_SelectionChangeCommitted(sender As Object, e As System.EventArgs)_
     Handles cboClient.SelectionChangeCommitted
        Me.cboCoverage.Requery()
        Me.cboCoverage.SelectedValue = 50022155  ' simplified for demo
 End Sub

This works fine when editing an existing record.  It fails on a new record with the following error:

System.InvalidCastException was unhandled by user code
  Message=Conversion from type 'DBNull' to type 'Integer' is not valid.
  Source=Microsoft.VisualBasic
  StackTrace:
       at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(Object Value)
       at ThomBillerBOLibrary.EventBO.FieldDescriptor.SetValue(Object component, Object value) in E:\ThomBiller\ThomBillerBOLibrary\ThomBillerBOLibrary\EventBO.Designer.vb:line 3003
       at System.Windows.Forms.BindToObject.SetValue(Object value)
       at System.Windows.Forms.Binding.PullData(Boolean reformat, Boolean force)
  InnerException:

Specifically, this is happening as the EventBO is trying to set the CLI_ID value based on the cboClient selection:

        Public Overrides Sub SetValue(ByVal component As Object, ByVal value As Object)
            Select Case Me.Field
                Case EventBOFieldNames.EVE_ID
                    DirectCast(component, EventBO).EVE_ID = CType(value, System.Int32)
                Case EventBOFieldNames.OLDPK
                    DirectCast(component, EventBO).OLDPK = CType(value, System.String)
                Case EventBOFieldNames.CLI_ID
                    DirectCast(component, EventBO).CLI_ID = CType(value, System.Int32)

What is so odd is that on a new EventBO record, I can either requery() the related cbo or set its selectedvalue without error, but not both.  If I am simply editing an existing EventBO record, I can do both.

TIA,

Larry

Hi Larry,
Sometimes, this kind of situation are better explained with a small and quick sample application, so here it is.  I created the small VB application which will show 2 comboboxes using data from the StrataFrameSample database.
It is pretty basic and straight forward:  When you select a customer from combobox 1, the CustomerNotes combo will be populated with all the notes for the selected customer.
Pay attention to the Population used in the comboxes as well as their events.  If the comboboxes are binded to the BO, then there is no need to update the 2nd combo SelectedValue since the binding will take care of that for you.
If I misunderstood you situation, then use this sample to duplicate your issue and post it again so we can all learn from it.

Edhy Rijo

Edhy,

Thank you for taking the time to put together a demo.  I was able to modify it (and misuse the poor Stataframe Sample database) to demonstrate my problem.

Again, the issue is not how to synchronize two combos.  I am able to do that as your demo demonstrated.

The problem is adding a step to the synchronization which involves setting a suggested value in combo 2.  The reason this is important to me is that in my medical billing application, a given client can have multiple insurance coverage records with different priorities, different dates, different services covered.  When I am entering charges, and I select a client, I want the coverage (cbo2) to refresh with only that client's coverages and "stop" on the one that fits the current date, service, etc.  In other words, on new records, when I select a client on cbo1 I want a recommended selection to appear on cbo2.  (On existing records, I will actually compare the existing cbo2 value to the recommended on and give them a warning if they have the wrong one.)

I got this working when editing an existing charge record.  It fails when working on a new charge.

It turns out that the problem is being cause by this second action:  setting cbo2.SelectedValue = <MyRecommendCoverage>.   Since this is being done from within the cbo1 selection process (within cbo1.SelectedChangeCommitted(() event handler) I think it is somehow short-circuiting the normal selection process on that combo.  The error is being thrown by the form's "ISA" as it tries to save the cbo1 selection.

Anyway, this revised demo will show the same error.  I had to misuse the Strataframe Sample database because I needed a table with two FKs on it.  So I picked OrderItems because it has two FKs to Orders and Products. 



You have to suspend some critical thinking when you use the demo, because in reality it makes no sense to have a OrderItemsMaintenanceForm like I built.  But on it, I use cboOrders and cboProducts as stand-ins for the truly related Client and Coverage tables in my real database.  Just think of them as cbo1 and cbo2, and pretend that cbo2 is a child of cbo1, and that when you pick something in cbo1, it not only refreshes cbo2 but also sets a suggested value.  This will throw the same error I have been getting when you try it on a New record.  Whew...



Thanks very much.

Larry