DataView and DataViewManager define the ListChanged event, which occurs when a row is added to or deleted from a DataView and DataViewManager object. The ListChangedEventHandler method handles the ListChanged event; it's as follows:
Public Delegate Sub ListChangedEventHandler(ByVal senderAs Object,ByVal e As ListChangedEventArges)
Where sender is the source of the event and e is ListChangedEventArgs, which contains the event
data
. Table 9-8 defines the ListChangedEventArgs members.
Table 9-8. The ListChangedEventArgs members
|
MEMBER
|
DESCRIPTION
|
|
ListChangedType
|
Returns the way that list changed
|
|
NewIndex
|
Returns the new index of the item in the list
|
|
OldIndex
|
Returns the old index of the item in the list
|
Listing 9-15 shows the OnListChanged event handler.
Listing 9-15.The OnListChanged event handler
Protected Shared Sub OnListChanged(ByVal sender As Object, ByVal args As System.ComponentModel.ListChangedEventArgs)
MessageBox.Show((("ListChanged: Type = " & args.ListChangedType & ", OldIndex = ") + args.OldIndex & ", NewIndex = ") + args.NewIndex)
End Sub
To test this application, you can create a
Windowsapplication and write the code in listing 9-16 on the form load or a button-click event handler. As you can see from listing 9-16, the code creates a DataView object, adds a new row to DataView, and then removes the first row from DataView. The adding and removing of rows is responsible for firing the OnListChanged event handler.
Listing 9-16. Adding, updating, and deleting rows of a DataView
Private Sub Form1_load(ByVal sender As Object,ByVal e As System.EventArgs)
Dim conn As New OleDbConnection()
Dim strDSN As String ="provider=Microsoft.Jet.OLEDB.4.0;" &"Data Source= C:/Northwind.mdb"
conn.ConnectionString = strDSN
Dim sql As String = "SELECT EmployeeID, LastName, FirstName FROM Employees"
' Opening Connection
conn.Open()
' Create a data Adapter
Dim daAs New OleDbDataAdapter(sql, conn)
' Create and fill DataSet
Dim dsAs New DataSet()
da.Fill(ds, "Employees")
Dim dv As DataView = ds.Tables("Employees").DefaultView
' Add DataView Event Handlers
AddHandler dv.ListChanged, AddressOf OnListChanged
' Add a row to the DataView
dv.AllowEdit = True
Dim rwAs DataRowView = dv.AddNew()
rw.BeginEdit()
rw("FirstName") ="FName"
rw("LastName") ="LName"
rw.EndEdit()
' Remove a row from the DataView
If dv.Count > 0Then
dv.Delete(0)
dv(0).Row.AcceptChanges()
End If
' Close the connection
conn.Close()
End Sub
CAUTION: As you can see from listing 9-16, the AcceptChanges() method removes a row permanently from the database. If you don't want to remove the row, call the RejectChanges() method.
The output of listing 9-16 looks like figure 9-11 and 9-12.
Figure 9-11. The ListChange events output after adding a new row
Figure 9-12. The ListChanged events output after deleting a row
Conclusion
Hope this article would have helped you in understanding working with DataView and DataViewManager Events in ADO.NET. See other articles on the website also for further reference.