Mastering Visual Basic .NET

526
Chapter 11 STORING DATA IN COLLECTIONS
Dim Shapes As New ArrayList()
Dim R1 As Rectangle
Shapes = CType(BFormatter.Deserialize(readFile), ArrayList)
Dim i As Integer
TextBox1.AppendText(“The ArrayList contains “ & Shapes.Count & _
“ objects” & vbCrLf & vbCrLf)
For i = 0 To Shapes.Count - 1
TextBox1.AppendText(Shapes(i).ToString & vbCrLf)
Next
End Sub
You can find the code presented in this section in the Serialization project on the CD. The
application consists of two buttons; the first persists the collection to disk, and the second reads
the file, re-creates the collection, and displays the objects read from the file.
Persisting a HashTable
We can now return to the WordFrequencies project and examine the code behind the menu of the
project. The Frequency Table menu contains four commands, which save the HashTable to, and
read it from, a text file and a binary file. The four commands of the menu are:
Command Effect
Save Binary Saves the HashTable to a binary file with default extension BIN
Load Binary Loads the HashTable with data from a binary file
Save SOAP Saves the HashTable to a text file with default extension TXT
Load Binary Loads the HashTable with data from a text file
The code behind the Save Binary command is shown in Listing 11.23. The code is actually quite
simple: it creates an instance of the BinaryFormatter class (variable Formatter) and uses its Serialize
method to persists the entire HashTable with a single statement.
Listing 11.23: Persisting the HashTable to a Binary File
Private Sub SaveBin(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles SaveBinary.Click
Dim saveFile As FileStream
SaveFileDialog1.DefaultExt = “BIN”
If SaveFileDialog1.ShowDialog = DialogResult.OK Then
saveFile = File.OpenWrite(SaveFileDialog1.FileName)
saveFile.Seek(0, SeekOrigin.End)
Dim Formatter As BinaryFormatter = New BinaryFormatter()
Formatter.Serialize(saveFile, WordFrequencies)
saveFile.Close()
End If
End Sub