bug in inherited controls?

[adshocker]

hi all,

on the custom inherited control i created, i noticed that when i bind my custom property to a data column, if that data column returns a value other than Null it always return a datarowstate of modified even if there were no changes.

to produce this issue, i have below a sample code for a test inherited control

Imports System.Windows.Forms
Imports System.ComponentModel

Public Class TestControl
  Inherits TextBox

  <Bindable(True)> _
  Public Property Value() As String
    Get
      Return MyBase.Text
    End Get
    Set(ByVal value As String)
      MyBase.Text = value
    End Set
  End Property
End Class

create a form, add the usual objects necessary for data bindings, (datasource, datatable). make sure the data column bound to this TestControl will return non null values.

also create a procedure for position changed to catch the datarowstate like below...

  Private Sub PositionChanged(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim rowstate As DataRowState = DataRowState.Unchanged
    rowstate = Me.YourDataSet.YourDataTable.Rows(Me.YourBindingSource.Position - 1).RowState
    MsgBox(rowstate.ToString)
  End Sub

Note that i used Position - 1 so that when you go to the next record, it will show you the rowstate of the previous record.

on your Form_Load add the ff:

AddHandler YourBindingSource.PositionChanged, AddressOf PositionChanged

don't make any changes to the current record before you go to the next record. you will see that the rowstate will still return Modified.

can anyone share their thoughts on this?

thanks

[jmcilhinney]

This is a really odd situation. I just used your code as you suggested and saw the behaviour you described. I messed around a bit and continued to see that behaviour with no real indication of why. I even took out the body of both the getter and the setter and still saw the same behaviour. I have no real idea of the cause but I'm interested enough to test a bit more so I'll let you know if I discover anything.

[adshocker]

i've now tried this on both vb 2005 express and vb 2008 express. unfortunately same behavior. i haven't tried on other editions yet as i'm still downloading vs 2008 pro trial version. although i'm not very confident that it has something to do with the editions.

Edit:
i've now tried it in vs studio 2008 pro trial and same behavior. i've also posted this in the microsoft forums and asking if it is a bug but have got no response yet.

[adshocker]

Updates:
I've also now tried creating a custom control which does not inherits any standard control but still same behavior.

i hope there's a fix to this.

[adshocker]

hi all,

after lots of research, somehow i manage to find some codes that made the rowstate stay as Unchanged but the problem now is that it stays Unchanged even if there are changes.

i added the following codes:

  Public Event ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs)

  Public Sub OnValueChanged(ByVal e As System.EventArgs)
    RaiseEvent ValueChanged(Me, e)
  End Sub

but i'm not really that familiar with events. i just read in this thread that you need to have an event for the property.

i'm hoping someone can help create the events properly.

thanks.

[jmcilhinney]

Are you raising the ValueChanged event when the Value changes? The idea is that, in the property setter, you check whether the new value is different to the old value and, if it is, you set the backing field and raise the event, i.e. call OnValueChanged, otherwise you do nothing.

I thought I'd tested whether an event would affect this but if you're saying it does then either I didn't or I did something wrong.

[adshocker]

hi,

thanks for the quick response.

actually it does have an effect on the DataRowState but it still needs a bit more tweaking.

anyways, after reading your advice, i now have

  Public Event ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

  Protected Overridable Sub OnValueChanged(ByVal e As System.EventArgs)
    RaiseEvent ValueChanged(Me, e)
  End Sub

  Property Value() As Nullable(Of DateTime)
    Get
      Return _Value
    End Get
    Set(ByVal value As Nullable(Of DateTime))

      If Not _Value.Equals(value) Then
        _Value = value
        Call OnValueChanged()
        If value.HasValue Then
          _Value = value
          MyBase.Text = value.Value.ToString(_FormatMask).ToUpper()
        Else
          MyBase.Text = String.Empty
        End If

      End If
    End Set
  End Property

however i get the error "Error 1: Argument not specified for parameter 'e' of 'Protected Overridable Sub OnValueChanged(e As System.EventArgs)'." on the line

Call OnValueChanged()

as i'm not sure what to pass to it since there's no System.EventArgs as parameter in the property.

please help.

thanks.

[jmcilhinney]

i'm not sure what to pass to it since there's no System.EventArgs as parameter in the property.

You're supposed to create the event args and provide the data. There is no data for a straight EventArgs though, so you just pass EventArgs.Empty.

While it's not going to hurt, there's no point setting _Value twice as you are. It's also not going to hurt but your use of the Call key word is redundant too. You can call a method without the Call key word, which exists for backward compatibility with VB6, which did require its use in certain situations.

[adshocker]

hi,

i've changed the code to meet your suggestion but somehow it still returns a rowState of Unchanged.

here's my new code:

    Public Event ValueChanged As EventHandler

    Protected Overridable Sub OnValueChanged(ByVal e As System.EventArgs)
        RaiseEvent ValueChanged(Me, e)
    End Sub

    <Bindable(True), _
     Browsable(False)> _
    Public Property Value() As Nullable(Of DateTime)
        Get
            Return _Value
        End Get
        Set(ByVal value As Nullable(Of DateTime))
            OnValueChanged(System.EventArgs.Empty)

            If Not _Value.Equals(value) Then
                _Value = value

                If value.HasValue Then
                    MyBase.Text = value.Value.ToString(_FormatMask).ToUpper()
                Else
                    MyBase.Text = String.Empty
                End If
            End If
        End Set
    End Property

something is not right with the even i think.