Error : Managed Debugging Assistant 'CallbackOnCollectedDelegate'

[Amr_Aly]

Hi Everybody,

I used this snippet to load customer name to a text box

Sub autocomplete()
conn = New OleDbConnection(cs)
conn.Open()

Dim cmd As New OleDbCommand("SELECT B_name FROM Customer", conn)
Dim ds As New DataSet
Dim da As New OleDbDataAdapter(cmd)
da.Fill(ds, "My List")

Dim col As New AutoCompleteStringCollection
Dim i As Integer

For i = 0 To ds.Tables(0).Rows.Count - 1
col.Add(ds.Tables(0).Rows(i)("B_name").ToString())
Next

B_name.AutoCompleteSource = AutoCompleteSource.CustomSource
B_name.AutoCompleteCustomSource = col
B_name.AutoCompleteMode = AutoCompleteMode.Suggest

conn.Close()

End Sub

But when i used the same code for Address in the same form an error occurs called 'CallbackOnCollectedDelegate'

Sub autocompleteAddress()
Using conn = New OleDbConnection(cs)
conn.Open()

Using cmd As New OleDbCommand
cmd.Connection = conn
cmd.CommandText = "SELECT B_Address FROM Customer"

Using ds As New DataSet, da As New OleDbDataAdapter(cmd)
da.Fill(ds, "List")

Dim acsc As New AutoCompleteStringCollection
Dim i As Integer

For i = 0 To ds.Tables(0).Rows.Count - 1
acsc.Add(ds.Tables(0).Rows(i)("B_Address").ToString())
Next

B_Address.AutoCompleteSource = AutoCompleteSource.CustomSource
B_Address.AutoCompleteCustomSource = acsc
B_Address.AutoCompleteMode = AutoCompleteMode.Suggest

End Using
End Using
End Using

End Sub

I used this snippets as follows

Private Sub Panel1_Enter(sender As Object, e As EventArgs) Handles Panel1.Enter
autocomplete()
End Sub


Private Sub B_name_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles B_name.Validating
autocompleteAddress()
End Sub

The full message says :

Additional information: A callback was made on a garbage collected delegate of type 'System.Windows.Forms!System.Windows.Forms.NativeMethods+WndProc::Invoke'. This may cause application crashes, corruption and data loss. When passing delegates to unmanaged code, they must be kept alive by the managed application until it is guaranteed that they will never be called.

I searched here and i found a same problem with combo boxes ..... Only solution came to my mind that i delete one of the both subrotines , and change the text box of address to combo box , but i think there is another solution to this problem ......



Any suggestions ...

Thanks in advance ......


Regards From Amr_Aly

Continue reading...