C# 4 and .NET 4

1374 ❘ ChaPTer 46 messAGe QueuinG
using System.Windows.Threading;
namespace Wrox.ProCSharp.Messaging
{
public partial class CourseOrderReceiverWindow: Window
{
private MessageQueue orderQueue;
public CourseOrderReceiverWindow()
{
InitializeComponent();
string queueName = CourseOrder.CourseOrderQueueName;
orderQueue = new MessageQueue(queueName);
orderQueue.Formatter = new XmlMessageFormatter(
new Type[]
{
typeof(CourseOrder),
typeof(Customer),
typeof(Course)
});
}
// start the task that fills the ListBox with orders
Task t1 = new Task(PeekMessages);
t1.Start();
code snippet CourseOrderReceiver/CourseOrderReceiverWindow.xaml.cs
The task’s main method, PeekMessages(), uses the enumerator of the message queue to display all
messages. Within the while loop, the messagesEnumerator checks to see if there is a new message in the
queue. If there is no message in the queue, the thread waits three hours for the next message to arrive
before it exits.
To display every message from the queue in the list box, the thread cannot directly write the text to the
list box, but needs to forward the call to the list box’s creator thread. Because WPF controls are bound to a
single thread, only the creator thread is allowed to access methods and properties. The Dispatcher
.Invoke() method forwards the request to the creator thread:
private void PeekMessages()
{
using (MessageEnumerator messagesEnumerator =
orderQueue.GetMessageEnumerator2())
{
while (messagesEnumerator.MoveNext(TimeSpan.FromHours(3)))
{
var labelId = new LabelIdMapping()
{
Id = messagesEnumerator.Current.Id,
Label = messagesEnumerator.Current.Label
};
Dispatcher.Invoke(DispatcherPriority.Normal,
new Action(AddListItem),
labelId);
}
}
MessageBox.Show("No orders in the last 3 hours. Exiting thread",
"Course Order Receiver", MessageBoxButton.OK,
MessageBoxImage.Information);
}
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