This is the first program I've tried to write in vb so I'll apologize
in advance for my terrible code.  :)

I've got a form with a tab control on it.  I'm working on the first
tab, binding data to controls in it.  So far I load data, the
navigation buttons and search button work, and I can add data.
Occassionally I get a ConstraintException and I can't figure out why.
The exception gets thrown right after my Update() which is in a
try/catch block.  No exception is thrown during the try/catch, but one
is thrown during the next statement to adjust the position of
bindingcontext.

I'm using visual studio.net professional on windows xp professional
with an msde db.

If you need any other info to help out feel free to post a reply or
send me email.  Thanks in advance.

Here's all the code I can think of that could be relevant:

Public Class frmStudio
   Inherits System.Windows.Forms.Form
   Dim ctrl As Control
   Dim errNumber As Integer

   Public Sub TryUpdate(ByRef da As
System.Data.SqlClient.SqlDataAdapter, _
   ByRef dt As System.Data.DataTable, ByRef er As Integer)
       Try
           da.Update(dt)
       Catch err As System.Data.SqlClient.SqlException
           er = err.Number
           If er = 2627 Then
               MessageBox.Show("School name " & txtSchoolName.Text &
" already exists." _
               & "  Change the name or delete this record and edit
the other version.")
           Else
               MessageBox.Show(err.Message.ToString)
               MessageBox.Show(err.Number.ToString)
           End If
       Catch cserr As System.Data.ConstraintException
           er = -1
           MessageBox.Show(cserr.Message.ToString)
       Catch ex As Exception
           MessageBox.Show(ex.Message.ToString)
       End Try
   End Sub
   Public Sub DisableControls(ByRef tpctrl As TabPage)
       For Each ctrl In tpctrl.Controls
           ctrl.Enabled = False
       Next
   End Sub

   Public Sub EnableControls(ByRef tpctrl As TabPage)
       For Each ctrl In tpctrl.Controls
           ctrl.Enabled = True
       Next
   End Sub

   Public Sub SetNavigationStatesStudents()
       If Me.BindingContext(DsAll, "Students").Count = 0 Then
           DisableControls(tpStudents)
           btnStudentNew.Enabled = True
       Else
           EnableControls(tpStudents)
       End If
   End Sub

   Public Sub SetNavigationStatesSchools()
       If dvSchools.Count < 2 Then
           ' there's less than 2 records so disable all navigation
           btnSchoolFirstRecord.Enabled = False
           btnSchoolPreviousRecord.Enabled = False
           btnSchoolNextRecord.Enabled = False
           btnSchoolLastRecord.Enabled = False
           lblSchoolCurrentRecord.Text =
(Me.BindingContext(dvSchools).Position + 1).ToString _
           & " of " & dvSchools.Count.ToString
       ElseIf dvSchools.Count = Me.BindingContext(dvSchools).Position
+ 1 Then
           ' we're on the last record so disable forward navigation
and enable backward
           btnSchoolFirstRecord.Enabled = True
           btnSchoolPreviousRecord.Enabled = True
           btnSchoolNextRecord.Enabled = False
           btnSchoolLastRecord.Enabled = False
           lblSchoolCurrentRecord.Text =
(Me.BindingContext(dvSchools).Position + 1).ToString _
           & " of " & dvSchools.Count.ToString
       ElseIf Me.BindingContext(dvSchools).Position = 0 Then
           ' we're on the first record so disable backward navigation
and enable forward
           btnSchoolFirstRecord.Enabled = False
           btnSchoolPreviousRecord.Enabled = False
           btnSchoolNextRecord.Enabled = True
           btnSchoolLastRecord.Enabled = True
           lblSchoolCurrentRecord.Text =
(Me.BindingContext(dvSchools).Position + 1).ToString _
           & " of " & dvSchools.Count.ToString
       Else
           ' we're in the middle of the records so enable all
navigation controls
           btnSchoolFirstRecord.Enabled = True
           btnSchoolPreviousRecord.Enabled = True
           btnSchoolNextRecord.Enabled = True
           btnSchoolLastRecord.Enabled = True
           lblSchoolCurrentRecord.Text =
(Me.BindingContext(dvSchools).Position + 1).ToString _
           & " of " & dvSchools.Count.ToString
       End If

   End Sub

   Public Sub SetControlStatesSchools()
       If dvSchools.Count = 0 Then
           DisableControls(tpSchools)
           btnSchoolNew.Enabled = True
           txtSchoolSearchPattern.Enabled = True
           btnSchoolSearch.Enabled = True
       Else
           EnableControls(tpSchools)
       End If
       SetNavigationStatesSchools()
   End Sub

   Public Sub SetControlStatesStudents()
       If Me.BindingContext(DsAll, "Students").Count = 0 Then
           DisableControls(tpStudents)
           btnStudentNew.Enabled = True
       Else
           EnableControls(tpStudents)
       End If
       SetNavigationStatesStudents()
   End Sub

   Public Sub New()
       MyBase.New()

       'This call is required by the Windows Form Designer.
       InitializeComponent()

       'Add any initialization after the InitializeComponent() call
       errNumber = 0
       Try
           DsAll.Clear()
           daStudents.Fill(DsAll)
           daSchools.Fill(DsAll)
           daLessons.Fill(DsAll)
           SetControlStatesStudents()
           SetControlStatesSchools()
       Catch err As System.Data.SqlClient.SqlException
           MessageBox.Show(err.Message.ToString)
       Catch ex As Exception
           MessageBox.Show(ex.Message.ToString)
       End Try
   End Sub

   Private Sub btnSchoolNew_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnSchoolNew.Click
       Dim drNew As System.Data.DataRowView

       'call update in case changes were made to the current record
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           'create a new row and add it to the dataset, binding it to
the form
           drNew = Me.dvSchools.AddNew()
           drNew("lessonSite") = 0
           drNew("schoolName") = "<New School>"
           TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
           If errNumber = 0 Then
               Me.BindingContext(dvSchools).Position = _
                               Me.BindingContext(dvSchools).Count - 1

               EnableControls(tpSchools)
               SetNavigationStatesSchools()
               txtSchoolName.Focus()
               txtSchoolName.SelectAll()
           Else
               errNumber = 0
           End If
       Else
           errNumber = 0
       End If
       
   End Sub

   Private Sub btnSchoolLastRecord_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnSchoolLastRecord.Click
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           Me.BindingContext(Me.dvSchools).Position =
Me.BindingContext(Me.dvSchools).Count - 1
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub

   Private Sub btnSchoolFirstRecord_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnSchoolFirstRecord.Click
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           Me.BindingContext(Me.dvSchools).Position = 0
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub

   Private Sub btnSchoolPreviousRecord_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnSchoolPreviousRecord.Click
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           '<THIS NEXT LINE IS WHERE THE CONSTRAINTEXCEPTION WAS
THROWN.
           'IT COMPLAINED ABOUT A SCHOOLID (primary key) THAT ALREADY
EXISTED.
           'SCHOOLID IS AN AUTOINCREMENT COLUMN IN MY DB
           Me.BindingContext(Me.dvSchools).Position -= 1
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub

   Private Sub btnSchoolNextRecord_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnSchoolNextRecord.Click
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           Me.BindingContext(Me.dvSchools).Position += 1
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub

   Private Sub btnSchoolDelete_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnSchoolDelete.Click
       Me.dvSchools.Delete(Me.BindingContext(Me.dvSchools).Position)
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           SetControlStatesSchools()
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub

   Private Sub btnSchoolSearch_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnSchoolSearch.Click
       TryUpdate(Me.daSchools, Me.DsAll.Schools, errNumber)
       If errNumber = 0 Then
           dvSchools.RowFilter = "schoolName LIKE '*" &
txtSchoolSearchPattern.Text & "*'"
           SetControlStatesSchools()
           SetNavigationStatesSchools()
       Else
           errNumber = 0
       End If
   End Sub
End Class