Can anyone explain to me what the following line of C# code does?
public event EventHandler<DataEventArgs<BusinessEntities.Employee>> EmployeeSelected = delegate { };
The bit that's really got me stumped is the delegate { }
piece at the end. For a bit more context, the sample from the EmployeesListView.xaml.cs in the ViewInjection sample that ships with PRISM 2. The full class definition is shown below:
/// <summary>
/// Interaction logic for EmployeesListView.xaml
/// </summary>
public partial class EmployeesListView : UserControl, IEmployeesListView
{
public EmployeesListView()
{
InitializeComponent();
}
public ObservableCollection<BusinessEntities.Employee> Model
{
get { return this.DataContext as ObservableCollection<BusinessEntities.Employee>; }
set { this.DataContext = value; }
}
public event EventHandler<DataEventArgs<BusinessEntities.Employee>> EmployeeSelected = delegate { };
private void EmployeesList_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (e.AddedItems.Count > 0)
{
BusinessEntities.Employee selected = e.AddedItems[0] as BusinessEntities.Employee;
if (selected != null)
{
EmployeeSelected(this, new DataEventArgs<BusinessEntities.Employee>(selected));
}
}
}
}
This bit:
delegate {}
just creates a "no-op" delegate of the appropriate type. That delegate is then assigned to the backing variable for the event. It's a simple way to avoid having to do null checks when raising an event - you always have at least one handler, which is the no-op handler.
It means that this code can be simple:
EmployeeSelected(this, new DataEventArgs<BusinessEntities.Employee>(selected));
Instead of:
EventHandler<DataEventArgs<BusinessEntities.Employee>> handler =EmployeeSelected;
if (handler != null)
{
handler(this, new DataEventArgs<BusinessEntities.Employee>(selected));
}
It's setting it to an anonymous method that does nothing basically. Why I'm not sure, maybe to avoid a check or something but I would consider that quite sloppy.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.