SQL dependency on relational tables - sql

Question

I have two related tables (tbVehicles and tbVehiclesDoc) I am running the below sql dependency but it is firring many time and my program freezes. please assist.
I want the program to update these tables when another user modifies them.
my Code:
Public Sub getdata()
Try
If tbdataset.Tables.Contains("tbVehicles") Then
If tbdataset.Tables("tbVehiclesDoc") IsNot Nothing Then
For f As Integer = tbdataset.Tables("tbVehiclesDoc").ChildRelations.Count - 1 To 0 Step -1
tbdataset.Tables("tbVehiclesDoc").ChildRelations(f).ChildTable.Constraints.Remove(tbdataset.Tables("tbVehiclesDoc").ChildRelations(f).RelationName)
tbdataset.Tables("tbVehiclesDoc").ChildRelations.RemoveAt(f)
Next
tbdataset.Tables("tbVehiclesDoc").ChildRelations.Clear()
tbdataset.Tables("tbVehiclesDoc").ParentRelations.Clear()
tbdataset.Tables("tbVehiclesDoc").Constraints.Clear()
tbdataset.Tables.Remove("tbVehiclesDoc")
End If
tbdataset.Tables.Remove("tbVehicles")
tbdataset.EnforceConstraints = True
End If
gridVehicles.DataSource = Nothing
Catch ex As Exception
MsgBox(ex.ToString)
' Exit Sub
End Try
command.Notification = Nothing
Dim dependency As New SqlDependency(command)
AddHandler dependency.OnChange, AddressOf dependency_OnChange
Dim adapter As New SqlDataAdapter(command)
adapter.Fill(tbdataset, "tbVehicles")
'----
End Sub
Private Sub toupdate()
If CanRequestNotifications() Then
If connection Is Nothing Then
connection = New SqlConnection(GetConnectionString())
connection.Open()
End If
If connection.State = ConnectionState.Closed Then
connection.Open()
End If
If command Is Nothing Then
command = New SqlCommand(GETSQL(), connection)
End If
End If
getdata()
End Sub
Private Function GETSQL() As String
Return "Select Rtrim(VehcID) as VehcID,RTrim(VehcModel), Rtrim(VehcRegNo) as VehcRegNo, Rtrim(VehcFourWheel), Rtrim(VehcCondition), Rtrim(VehcLastKM),Rtrim(VehcBranch), Rtrim(VehcDepartment), Rtrim(VehcDriver), Rtrim(VehcRemarks), VehcPic from dbo.tbVehicles"
End Function
Private Sub dependency_OnChange(ByVal sender As Object, ByVal e As SqlNotificationEventArgs)
' This event will occur on a thread pool thread.
' It is illegal to update the UI from a worker thread
' The following code checks to see if it is safe
' update the UI.
Dim i As ISynchronizeInvoke = CType(Me, ISynchronizeInvoke)
' If InvokeRequired returns True, the code
' is executing on a worker thread.
If i.InvokeRequired Then
' Create a delegate to perform the thread switch
Dim tempDelegate As New OnChangeEventHandler( _
AddressOf dependency_OnChange)
Dim args() As Object = {sender, e}
' Marshal the data from the worker thread
' to the UI thread.
i.BeginInvoke(tempDelegate, args)
Return
End If
' Remove the handler since it's only good
' for a single notification
Dim dependency As SqlDependency = _
CType(sender, SqlDependency)
RemoveHandler dependency.OnChange, _
AddressOf dependency_OnChange
' Reload the dataset that's bound to the grid.
getdata()
End Sub