Lesson 1: Serializing Objects in VB.NET

Generator QR in VB.NET Lesson 1: Serializing Objects

Deserializing an object allows you to create a new object based on stored data. Essentially, deserializing restores a saved object. At a high level, the steps for deserializing an object are as follows: 1. Create a stream object to read the serialized output. 2. Create a BinaryFormatter object. 3. Create a new object to store the deserialized data. 4. Call the BinaryFormatter.Deserialize method to deserialize the object, and cast it to the correct type. At the code level, the steps for deserializing an object are easy to implement. The following Console application which requires the System.IO, System.Runtime.Serialization, and System.Runtime.Serialization.Formatters.Binary namespaces demonstrates how to read and display the serialized string data saved in an earlier example:

' VB ' Open file from which to read the data Dim fs As FileStream = New FileStream("SerializedString.Data", FileMode.Open) ' Create a BinaryFormatter object to perform the deserialization Dim bf As BinaryFormatter = New BinaryFormatter ' Create the object to store the deserialized data Dim data As String = "" ' Use the BinaryFormatter object to deserialize the data from the file data = DirectCast(bf.Deserialize(fs), String) ' Close the file fs.Close ' Display the deserialized string Console.WriteLine(data) // C# // Open file from which to read the data FileStream fs = new FileStream("SerializedString.Data", FileMode.Open); // Create a BinaryFormatter object to perform the deserialization BinaryFormatter bf = new BinaryFormatter(); // Create the object to store the deserialized data string data = ""; // Use the BinaryFormatter object to deserialize the data from the file data = (string)bf.Deserialize(fs);

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// Close the file fs.Close(); // Display the deserialized string Console.WriteLine(data);

Deserializing a more complex object, such as DateTime, works exactly the same. The following code sample displays the day of the week and the time stored by a previous code sample:

' VB ' Open file from which to read the data Dim fs As FileStream = New FileStream("SerializedDate.Data", FileMode.Open) ' Create a BinaryFormatter object to perform the deserialization Dim bf As BinaryFormatter = New BinaryFormatter ' Create the object to store the deserialized data Dim previousTime As DateTime = New DateTime ' Use the BinaryFormatter object to deserialize the data from the file previousTime = DirectCast(bf.Deserialize(fs), DateTime) ' Close the file fs.Close ' Display the deserialized time Console.WriteLine(("Day: " + (previousTime.DayOfWeek + (", Time: " _ + previousTime.TimeOfDay.ToString)))) // C# // Open file from which to read the data FileStream fs = new FileStream("SerializedDate.Data", FileMode.Open); // Create a BinaryFormatter object to perform the deserialization BinaryFormatter bf = new BinaryFormatter(); // Create the object to store the deserialized data DateTime previousTime = new DateTime(); // Use the BinaryFormatter object to deserialize the data from the file previousTime = (DateTime) bf.Deserialize(fs); // Close the file fs.Close(); // Display the deserialized time Console.WriteLine("Day: " + previousTime.DayOfWeek + ", Time: " + previousTime.TimeOfDay.ToString());

As these code samples demonstrate, storing and retrieving objects requires only a few lines of code, no matter how complex the object is (assuming the object supports serialization, as discussed later in this chapter).

Within the runtime, deserialization can be a complex process. The runtime proceeds through the deserialization process sequentially, starting at the beginning and working its way through to the end. The process gets complicated if an object in the serialized stream refers to another object. If an object references another object, the Formatter (discussed in more detail in Lesson 3 of this chapter, Custom Serialization ) queries the ObjectManager to determine whether the referenced object has already been deserialized (a backward reference), or whether it has not yet been deserialized (a forward reference). If it is a backward reference, the Formatter immediately completes the reference. However, if it is a forward reference, the Formatter registers a fixup with the ObjectManager. A fixup is the process of finalizing an object reference after the referenced object has been deserialized. Once the referenced object is deserialized, ObjectManager completes the reference.