Hello!

I really hope somebody can help me!

I'm trying to build a layered solution, with a class project as data layer (project B) anda windows form project (project A)as user interface. On the data layer part, I would like to use the SQLDependency to keep my datasets always in sync with the database.

On the form (project A) i have the following code:

Public Class Form2

Private WithEvents mCinemas As CS_DataLayer.clsCinemas

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
LoadData()
End Sub

Private Sub mCinemas_DataChanged() Handles mCinemas.DataChanged
LoadData()
End Sub

Private Sub LoadData()
If IsNothing(mCinemas) Then
mCinemas = New CS_DataLayer.clsCinemas
End If
DataGridView1.DataSource = mCinemas.Cinemas
DataGridView1.Refresh()
End Sub

End Class

And the code from clsCinemas (project B):

Imports System.ComponentModel
Imports System.Data.SqlClient

Public Class clsCinemas
Private connection As SqlConnection
Private command As SqlCommand
Private _cinemas As DataSet
Public Event DataChanged()

Public Property Cinemas() As DataSet
Get
Return _Cinemas
End Get
Set(ByVal value As DataSet)
_Cinemas = value
End Set
End Property

Public Sub New()
SqlDependency.Start(My.Settings.ConnectionString)
If connection Is Nothing Then
connection = New SqlConnection(My.Settings.ConnectionString)
End If
If command Is Nothing Then
command = New SqlCommand("SELECT name FROM tblTest", connection)
End If
If _cinemas Is Nothing Then
_cinemas = New DataSet()
End If
GetData()
End Sub

Private Sub GetData()
_cinemas.Clear()
command.Notification = Nothing
Dim dependency As New SqlDependency(command)
AddHandler dependency.OnChange, AddressOf dependency_OnChange
Using adapter As New SqlDataAdapter(command)
adapter.Fill(_cinemas)
End Using
End Sub

Private Sub dependency_OnChange(ByVal sender As Object, ByVal e As SqlNotificationEventArgs)
Dim dependency As SqlDependency = CType(sender, SqlDependency)
RemoveHandler dependency.OnChange, AddressOf dependency_OnChange
GetData()
RaiseEvent DataChanged()
End Sub

Protected Overrides Sub Finalize()
SqlDependency.Stop(My.Settings.ConnectionString)
If connection IsNot Nothing Then
connection.Close()
End If
MyBase.Finalize()
End Sub

End Class

When I try to run the application, I get the following error message:
"Cross-thread operation not valid: Control 'DataGridView1' accessed from a thread other than the thread it was created on."

Can somebody please help me, as I don't know what is going wrong. It's probably something really easy !?!

Thank you very much!

When I try to run the application, I get the following error message:
"Cross-thread operation not valid: Control 'DataGridView1' accessed from a thread other than the thread it was created on."

Can somebody please help me, as I don't know what is going wrong. It's probably something really easy !?!

This is a WinForms programming issue rather than a SQL one. You need to invoke UI control methods on the same thread that owns the window because UI controls are not thread safe.The example below shows how you might do this.

Private Delegate Sub RefreshDataDelegate()

Private Sub LoadData()

If IsNothing(mCinemas) Then
mCinemas = New CS_DataLayer.clsCinemas
End If
If DataGridView1.InvokeRequired Then
DataGridView1.Invoke(New RefreshDataDelegate(addressof RefreshData) )
Else
RefreshData()
End

End Sub

Private Sub RefreshData()

DataGridView1.DataSource = mCinemas.Cinemas
DataGridView1.Refresh()

End Sub

---

Dan Guzman, SQL Server MVP, http://weblogs.sqlteam.com/dang/

When I try to run the application, I get the following error message:
"Cross-thread operation not valid: Control 'DataGridView1' accessed from a thread other than the thread it was created on."

Can somebody please help me, as I don't know what is going wrong. It's probably something really easy !?!

This is a WinForms programming issue rather than a SQL one. You need to invoke UI control methods on the same thread that owns the window because UI controls are not thread safe.The example below shows how you might do this.

Private Delegate Sub RefreshDataDelegate()

Private Sub LoadData()

If IsNothing(mCinemas) Then
mCinemas = New CS_DataLayer.clsCinemas
End If
If DataGridView1.InvokeRequired Then
DataGridView1.Invoke(New RefreshDataDelegate(addressof RefreshData) )
Else
RefreshData()
End

End Sub

Private Sub RefreshData()

DataGridView1.DataSource = mCinemas.Cinemas
DataGridView1.Refresh()

End Sub

---

Dan Guzman, SQL Server MVP, http://weblogs.sqlteam.com/dang/