MSDN Magazine - December 2008 - (Page 26)

tionChangedEventArgs parameter. This object provides information about what changed within the collection and also provides five interesting properties, which are listed in Figure 6. Given all this information, your event handler can determine exactly what occurred within the collection that triggered the event. The sample code merely uses the Action property, updating the list of integers in the ComboBox control if the collection changed size: If e.Action = NotifyCollectionChangedAction.Add Or _ e.Action = NotifyCollectionChangedAction.Remove Then Although it’s not pertinent to the discussion of the ObservableCollection class, it is interesting to see how the code fills in the list of indexes in the ComboBox control: Private Sub SetComboDataSource() ' Set the list of integers shown in the ' combo box: ItemComboBox.ItemsSource = _ Enumerable.Range(0, Data.Count) End Sub In order for the sample application to be notified if you change properties of an item within the collection, you have to write a little more code. Each of the properties within the class raises the PropertyChanged event each time some code changes the value of the property. (Of course, it’s up to the author of the specific class to make sure that property changes raise the PropertyChanged event, because it doesn’t happen automatically. The Customer class’s Name property, as you’ve seen, does this.) Within the MainWindow class, you’ll find the HookupChangeEventHandler procedure, which hooks up the PropertyChanged event for an individual Customer object: Private Sub HookupChangeEventHandler(ByVal cust As Customer) ' Add a PropertyChanged event handler for ' the specified Customer instance: AddHandler cust.PropertyChanged, _ AddressOf HandlePropertyChanged End Sub Rather than performing some loop to generate a list containing integers between 0 and the highest-numbered index in the collection, this code simply calls the Enumerable.Range method to retrieve a collection of integers starting at 0 and containing Data.Count values. The code sets the ItemsSource property of the ComboBox control to the returned collection—and that’s all there is to it! (If you are looking for more information on the Enumerable class, you should read my previous two Advanced Basics columns: msdn.microsoft.com/ magazine/cc700332 and msdn.microsoft.com/magazine/cc793963.) The HookupChangeEventHandlers procedure hooks up event handlers for each Customer within the ObservableCollection of customers, like so: Private Sub HookupChangeEventHandlers() For Each cust As Customer In Data HookupChangeEventHandler(cust) Next End Sub When the window loads or you click the Reset button, the code calls the HookupChangeEventHandlers procedure. When you click 26 msdn magazine Advanced Basics http://msdn.microsoft.com/magazine/cc700332 http://msdn.microsoft.com/magazine/cc793963 http://msdn.microsoft.com/magazine/cc700332 http://www.datadynamics.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - December 2008

MSDN Magazine - December 2008 Contents Toolbox CLR Inside Out Advanced Basics Cutting Edge Patterns In Practice Team System Real-World WF Visual Studio OBA Tools SOA Data Access Geneva Framework Test Run Foundations Windows With C++ Going Places End Bracket

MSDN Magazine - December 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.