Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

want a more compact format, opt for the binary .NET Framework formatter andconsider using a ghost class, as described in Chapter 9.Reviewing and Rejecting ChangesUsers of the sample application enter changes through the interface of the DataGridcontrol. Each change is detected, and controls in the user interface are enabled anddisabled to reflect those changes. For example, the Review Changes button is enabledif there are changes to review.Detecting Ongoing ChangesIn a Windows Forms application, data sources associated with data-bound controls aremanaged by a special breed of component—the binding manager.BindingManagerBase is the abstract class for binding managers; the actual classes youwill work with are CurrencyManager and PropertyManager.The PropertyManager class keeps track of a simple binding between a data-boundcontrol property and a data source scalar value. The CurrencyManager class plays amore sophisticated role. CurrencyManager handles complex data binding andmaintains bindings between a data source and all the list controls (for example, theDataGrid control) that bind to it or to one of its member tables. The CurrencyManagerclass takes care of synchronizing the controls bound to the same data source andprovides a uniform interface for clients to access the current item for the list. Bothmanager classes have a property named Current and fire position-related events suchas ItemChanged. The Current property returns the currently selected item, whateverthat is for the particular binding class. For example, for the DataGrid class, the currentitem is the nth bound element—that is, a DataRow object if a DataTable is bound, or astring if an array of strings is bound.To access the binding manager for a particular data source, you use the Form object'sBindingContext collection, as shown here:CurrencyManager m_bmbEmployees;m_bmbEmployees = (CurrencyManager) BindingContext[m_dataSet,"Employees"];m_bmbEmployees.ItemChanged +=new ItemChangedEventHandler(CurrentChanged);This code also registers a handler for the ItemChanged event. The binding managerautomatically fires the event whenever an item in the bound data source—theEmployees table in the grid's DataSet object—changes. In other words, the handlerexecutes whenever a change occurs and refreshes the application's user interfaceaccordingly.Selecting Changed RowsAs mentioned, the DataSet object registers all the changes but retains the originalvalues of the modified rows. Thanks to these features, setting up a form to review thecurrent changes is not at all difficult. Let's see how to proceed.The idea is to create a view of the table—possibly a copy of the table that includes onlythe changes. The GetChanges method can be used to obtain a copy of the DataTableobject (or the DataSet object) that includes only the changed rows, as shown here:DataTable dtChanges =m_dataSet.Tables["Employees"].GetChanges();if (dtChanges == null)return;DataView dv = dtChanges.DefaultView;381