C# 4 and .NET 4

1368 ❘ ChaPTer 46 messAGe QueuinG
A message formatter implements the interface
IMessageFormatter. Three message formatters are
available with the namespace System.Messaging:
➤
➤
➤
The XmlMessageFormatter is the default
formatter. It serializes objects using XML. See
Chapter 33, “Manipulating XML,” for more on
XML formatting.
With the BinaryMessageFormatter, messages are
serialized in a binary format. These messages are
shorter than the messages formatted using XML.
The ActiveXMessageFormatter is a binary
formatter so that messages can be read or written
with COM objects. Using this formatter, it is
possible to write a message to the queue with a
.NET class and to read the message from the queue
with a COM object or vice versa.
The sample message shown in Figure 46-8 with XML is
formatted with the BinaryMessageFormatter in Figure 46-9.
sending Complex Messages
Instead of passing strings, it is possible to pass objects to the Send() method of the MessageQueue class.
The type of the class must fulfill some specific requirements, but they depend on the formatter.
For the binary formatter, the class must be serializable with the [Serializable] attribute. With the
.NET runtime serialization, all fields are serialized (this includes private fields). Custom serialization can
be defined by implementing the interface ISerializable. You can read more about the .NET runtime
serialization in Chapter 29, “Manipulating Files and the Registry.”
XML serialization takes place with the XML formatter. With XML serialization, all public fields
and properties are serialized. The XML serialization can be influenced by using attributes from the
System.Xml.Serialization namespace. You can read more about XML serialization in Chapter 33.
receiving messages
To read messages, again, you can use the MessageQueue class. With the Receive() method, a single
message is read and removed from the queue. If messages are sent with different priorities, the message
with the highest priority is read. Reading messages with the same priority may mean that the first message
sent is not the first message read because the order of messages across the network is not guaranteed. For a
guaranteed order, you should use transactional message queues.
In the following example, a message is read from the private queue MyPrivateQueue. Previously, a simple
string was passed to the message. When you read a message using the XmlMessageFormatter, you have
to pass the types of the objects that are read to the constructor of the formatter. In the example, the
type System.String is passed to the argument array of the XmlMessageFormatter constructor. This
constructor allows either a String array that contains the types as strings to be passed or a Type array.
The message is read with the Receive() method, and then the message body is written to the console:
using System;
using System.Messaging;
namespace Wrox.ProCSharp.Messaging
{
class Program
{
figure 46-9
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