Working with DataView and DataViewManager Events in ADO.NET

This article has been excerpted from the book "A Programmer's Guide to ADO.NET in C#".

 

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 void ListChangedEventHandler(object sender, ListChangedEventArges e);

 

Where the sender is the source of the event and e is ListChangedEventArgs, which contains the event data. Table 9-8 defines ListChangedEventArgs members.

 

Table 9-8. The ListChangedEventArgs members

 

MEMBER	DESCRIPTION
ListChangedType	Returns the way that lists 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 static void OnListChanged(object sender, System.ComponentModel.ListChangedEventArgs args) {
    MessageBox.Show("ListChanged: Type = " + args.ListChangedType +
          ", OldIndex = " + args.OldIndex +
          ", NewIndex = " + args.NewIndex);
}

To test this application, you can create a Windows application 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 void Form1_load(object sender, System.EventArgs e) {
    OleDbConnection conn = new OleDbConnection();
    string strDSN = "provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source= C:/Northwind.mdb";
    conn.ConnectionString = strDSN;
    string sql = "SELECT EmployeeID, LastName, FirstName FROM Employees";
    // Opening Connection
    conn.Open();
    // Create a data Adapter
    OleDbDataAdapter da = new OleDbDataAdapter(sql, conn);
    // Create and fill DataSet
    DataSet ds = new DataSet();
    da.Fill(ds, "Employees");
    DataView dv = ds.Tables["Employees"].DefaultView;
    // Add DataView Event Handlers
    dv.ListChanged += new System.ComponentModel.ListChangedEventHandler(OnListChanged);
    // Add a row to the DataView
    dv.AllowEdit = true;
    DataRowView rw = dv.AddNew();
    rw.BeginEdit();
    rw["FirstName"] = "FName";
    rw["LastName"] = "LName";
    rw.EndEdit();
    // Remove a row from the DataView
    if (dv.Count > 0) {
        dv.Delete(0);
        dv[0].Row.AcceptChanges();
    }
    // Close the connection
    conn.Close();
}

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.

 

This essential guide to Microsoft's ADO.NET overviews C# then leads you toward deeper understanding of ADO.NET.