Array List as DataSource For LIstBox Bug?

[Zorpiedoman]

The problem is this:

I have a list box. I set an array list as the datasource. I remove an item
from the array list. I set the listbox datasource to nothing. I set the
listbox datasource to the array list again to refresh. Click on an item in
the list, and an Indexing error comes up. (in non-user code, it is trying to
get an element from the array that is greater than the number of items in the
array.)

To reproduce:

1. Create a WindowsForm Project with the following code.
2. Run the Project
3. Click on the third item in the list.
4. Click the Button (after the delete, the 'Four' item is selected)
5. Click the Button again. (after the delete, nothing is selected, but...)
6. Click on either item in the list - Error is generated.

HELP!

Thanks.

---------------------CODE to reproduce--------------------
Public Class Form1
Inherits System.Windows. Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

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

'Add any initialization after the InitializeCompo nent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Disp ose()
End If
End If
MyBase.Dispose( disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.Componen tModel.IContain er

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents ListBox1 As System.Windows. Forms.ListBox
Friend WithEvents Button1 As System.Windows. Forms.Button
<System.Diagnos tics.DebuggerSt epThrough()> Private Sub
InitializeCompo nent()
Me.ListBox1 = New System.Windows. Forms.ListBox
Me.Button1 = New System.Windows. Forms.Button
Me.SuspendLayou t()
'
'ListBox1
'
Me.ListBox1.Doc k = System.Windows. Forms.DockStyle .Top
Me.ListBox1.Loc ation = New System.Drawing. Point(0, 0)
Me.ListBox1.Nam e = "ListBox1"
Me.ListBox1.Siz e = New System.Drawing. Size(304, 251)
Me.ListBox1.Tab Index = 0
'
'Button1
'
Me.Button1.Loca tion = New System.Drawing. Point(208, 264)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing. Size(72, 24)
Me.Button1.TabI ndex = 1
Me.Button1.Text = "Button1"
'
'Form1
'
Me.AutoScaleBas eSize = New System.Drawing. Size(5, 13)
Me.ClientSize = New System.Drawing. Size(304, 300)
Me.Controls.Add (Me.Button1)
Me.Controls.Add (Me.ListBox1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout (False)

End Sub

#End Region

Private MyArrayList As New ArrayList

Private Class ItemClass
Implements IComparable
Private myID As Integer
Public Property ID() As Integer
Get
Return myID
End Get
Set(ByVal Value As Integer)
myID = Value
End Set
End Property
Private myValue As String
Public Property Value() As String
Get
Return myValue
End Get
Set(ByVal Value As String)
myValue = Value
End Set
End Property

Public Function CompareTo(ByVal obj As Object) As Integer Implements
System.ICompara ble.CompareTo
If TypeOf obj Is ItemClass Then
If DirectCast(obj, ItemClass).ID > Me.ID Then Return -1
If DirectCast(obj, ItemClass).ID < Me.ID Then Return 1
Return 0
End If
End Function
End Class

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load
Dim A As New ItemClass
A.ID = 1
A.Value = "One"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 2
A.Value = "Two"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 3
A.Value = "Three"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 4
A.Value = "Four"
MyArrayList.Add (A)
MyArrayList.Sor t()

Me.ListBox1.Dat aSource = MyArrayList
Me.ListBox1.Val ueMember = "ID"
Me.ListBox1.Dis playMember = "Value"
End Sub

Private Sub Button1_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button1.Click
MyArrayList.Rem oveAt(2)
MyArrayList.Sor t()

Me.ListBox1.Dat aSource = Nothing

Me.ListBox1.Dat aSource = MyArrayList
Me.ListBox1.Val ueMember = "ID"
Me.ListBox1.Dis playMember = "Value"
End Sub
End Class

--
--Zorpie

[Bernie Yaeger]

Hi Zorpie,

Did you try the listbox's refresh method?

HTH,

Bernie Yaeger

"Zorpiedoma n" <no*********@be atles.com> wrote in message
news:8E******** *************** ***********@mic rosoft.com...

The problem is this:

I have a list box. I set an array list as the datasource. I remove an
item
from the array list. I set the listbox datasource to nothing. I set the
listbox datasource to the array list again to refresh. Click on an item
in
the list, and an Indexing error comes up. (in non-user code, it is trying
to
get an element from the array that is greater than the number of items in
the
array.)

To reproduce:

1. Create a WindowsForm Project with the following code.
2. Run the Project
3. Click on the third item in the list.
4. Click the Button (after the delete, the 'Four' item is selected)
5. Click the Button again. (after the delete, nothing is selected,
but...)
6. Click on either item in the list - Error is generated.

HELP!

Thanks.

---------------------CODE to reproduce--------------------
Public Class Form1
Inherits System.Windows. Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

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

'Add any initialization after the InitializeCompo nent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Disp ose()
End If
End If
MyBase.Dispose( disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.Componen tModel.IContain er

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents ListBox1 As System.Windows. Forms.ListBox
Friend WithEvents Button1 As System.Windows. Forms.Button
<System.Diagnos tics.DebuggerSt epThrough()> Private Sub
InitializeCompo nent()
Me.ListBox1 = New System.Windows. Forms.ListBox
Me.Button1 = New System.Windows. Forms.Button
Me.SuspendLayou t()
'
'ListBox1
'
Me.ListBox1.Doc k = System.Windows. Forms.DockStyle .Top
Me.ListBox1.Loc ation = New System.Drawing. Point(0, 0)
Me.ListBox1.Nam e = "ListBox1"
Me.ListBox1.Siz e = New System.Drawing. Size(304, 251)
Me.ListBox1.Tab Index = 0
'
'Button1
'
Me.Button1.Loca tion = New System.Drawing. Point(208, 264)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing. Size(72, 24)
Me.Button1.TabI ndex = 1
Me.Button1.Text = "Button1"
'
'Form1
'
Me.AutoScaleBas eSize = New System.Drawing. Size(5, 13)
Me.ClientSize = New System.Drawing. Size(304, 300)
Me.Controls.Add (Me.Button1)
Me.Controls.Add (Me.ListBox1)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout (False)

End Sub

#End Region

Private MyArrayList As New ArrayList

Private Class ItemClass
Implements IComparable
Private myID As Integer
Public Property ID() As Integer
Get
Return myID
End Get
Set(ByVal Value As Integer)
myID = Value
End Set
End Property
Private myValue As String
Public Property Value() As String
Get
Return myValue
End Get
Set(ByVal Value As String)
myValue = Value
End Set
End Property

Public Function CompareTo(ByVal obj As Object) As Integer
Implements
System.ICompara ble.CompareTo
If TypeOf obj Is ItemClass Then
If DirectCast(obj, ItemClass).ID > Me.ID Then Return -1
If DirectCast(obj, ItemClass).ID < Me.ID Then Return 1
Return 0
End If
End Function
End Class

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load
Dim A As New ItemClass
A.ID = 1
A.Value = "One"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 2
A.Value = "Two"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 3
A.Value = "Three"
MyArrayList.Add (A)
A = New ItemClass
A.ID = 4
A.Value = "Four"
MyArrayList.Add (A)
MyArrayList.Sor t()

Me.ListBox1.Dat aSource = MyArrayList
Me.ListBox1.Val ueMember = "ID"
Me.ListBox1.Dis playMember = "Value"
End Sub

Private Sub Button1_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button1.Click
MyArrayList.Rem oveAt(2)
MyArrayList.Sor t()

Me.ListBox1.Dat aSource = Nothing

Me.ListBox1.Dat aSource = MyArrayList
Me.ListBox1.Val ueMember = "ID"
Me.ListBox1.Dis playMember = "Value"
End Sub
End Class

--
--Zorpie

[Zorpiedoman]

That does not refresh the data. The work-around so far is to Set the
SelectedIndex to -1 BEFORE removing the item from the arraylist. Then it
works fine, but this may not always be possible in real life.

-zorpy

"Bernie Yaeger" wrote:

Hi Zorpie,

Did you try the listbox's refresh method?

HTH,

Bernie Yaeger

[Larry Serflaten]

"Zorpiedoma n" <no*********@be atles.com> wrote

The problem is this:

I have a list box. I set an array list as the datasource. I remove an item
from the array list. I set the listbox datasource to nothing. I set the
listbox datasource to the array list again to refresh. Click on an item in
the list, and an Indexing error comes up.
Everywhere you have
Me.ListBox1.Dat aSource = MyArrayList
Use:
Me.ListBox1.Dat aSource = MyArrayList.Clo ne

HTH
LFS

[Larry Serflaten]

"Dennis" <De****@discuss ions.microsoft. com> wrote

Interesting! What is the logic (why does this work)? Any idea?

It may be that binding is an expensive operation such that they
included a test to see if the new object is the same as the old
object, and return early if they were the same.

So even though you changed the array, you assign the same
arraylist back to the DataSource property, which gets detected
as the same object as before. Since its the same object, they
skip tring to bind to it, because it is already bound to...

That is only my speculation.
LFS

[Dennis]

Thanks Larry. It would be like Microsoft to think they know better than us
what we want to do.

"Larry Serflaten" wrote:

"Dennis" <De****@discuss ions.microsoft. com> wrote

Interesting! What is the logic (why does this work)? Any idea?

It may be that binding is an expensive operation such that they
included a test to see if the new object is the same as the old
object, and return early if they were the same.

So even though you changed the array, you assign the same
arraylist back to the DataSource property, which gets detected
as the same object as before. Since its the same object, they
skip tring to bind to it, because it is already bound to...

That is only my speculation.
LFS

[Zorpiedoman]

However, my setting .datasource = nothing, then re-setting it to the array
list does the same thing, so this does not fix the problem.

[Zorpiedoman]

This is a rather costly solution... also, if any docking is being used, you
have just changed the z-order of the control and it could appear in an
unwanted place on the form. why do you think this would change anything
anyway?

"Cor Ligthert" wrote:

Zorpiedoman,

In my opinion is this as you wrote a bug, try this
\\\
MyArrayList.Rem oveAt(2)
MyArrayList.Sor t()
Me.Controls.Rem ove(ListBox1)
Me.Controls.Add (ListBox1)
///
Than it works as it should work in my opinion without that remove and add.

I hope this gives an idea

Cor

[Cor Ligthert]

> This is a rather costly solution... also, if any docking is being used,

you
have just changed the z-order of the control and it could appear in an
unwanted place on the form. why do you think this would change anything
anyway?

Because I tried it.

Cor

[Zorpiedoman]

Do you see my point, however, that this is not a viable solution?

"Cor Ligthert" wrote:

This is a rather costly solution... also, if any docking is being used,
you
have just changed the z-order of the control and it could appear in an
unwanted place on the form. why do you think this would change anything
anyway?

Because I tried it.

Cor