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5.4. Read and Write Files
If you need to work with text files or
raw binary data, VB 2005 provides a new solution that bypasses the
lower-level classes of System.IO for small files.
Now you can read and write text in a single atomic operation using
the My.Computer.FileSystem object. Best of all,
you no longer need to create streams, track your position, or clean
up afterward.
Note: At last, a way to read and write files without the
complexities of streams and stream readers.
5.4.1. How do I do that?
The My.Computer.FileIO object provides the
absolute quickest way to read or write the contents of a file. Its
secret lies in a few self-contained methods. These include:ReadAllText( )
Reads the content of a text file and
returns it as a single string.
ReadAllBytes( )
Reads the content of any file and returns
it as an array of bytes.
WriteAllText( )
Writes text as a string to a file in one
atomic operation. You can either add to an existing file or create a
new file, depending on whether you supply true or
False for the Boolean append
parameter.
WriteAllBytes( )
Writes a byte array to a file in a single
operation. You can either add to an existing file or create a new
file, depending on whether you supply true or
False for the Boolean append
parameter.
Example 5-4 creates a simple text file and then
reads it back into memory.
Example 5-4. Write a file in one step and read a file in one step
Imports System.IO
Module FileReadAndWrite
Public Sub Main( )
Dim Text As String = "This is line 1" & _
vbNewLine & "This is line 2" & _
vbNewLine & "This is line 3" & _
vbNewLine & "This is line 4"
' Write the file.
My.Computer.FileSystem.WriteAllText("c:\test.txt", Text, False)
' Read the file.
Console.WriteLine(My.Computer.FileSystem.ReadAllText("c:\test.txt"))
End Sub
End Module
5.4.2. What about...
...the limitations of this approach? The methods that
you'll find in the
My.Computer.FileSystem object are unmatched for
sheer convenience, but they aren't always
appropriate. Here are some reasons you might be better off using the
lower-level classes of the System.IO
namespace:You have an extremely large file, and you want to read and process
its contents one piece at a time, rather than load the entire file
into memory at once. This is a reasonable approach it
you're dealing with a long document, for example.You want to use other data types, like numbers or dates. In order to
use the My.Computer.FileIO methods to handle
numeric data, you'll need to first convert the
numbers into strings or byte arrays manually using other .NET
classes. On the other hand, if you use a
FileStream instead, you simply need to wrap it
with a BinaryReader or
BinaryWriter.You want to use other stream-based .NET features, such as compression
(explained in the next lab, "Compress and Decompress
Data"), object serialization, or encryption.
The core .NET classes for reading and writing files are found in the
System.IO namespace and haven't
changed in .NET 2.0. The most useful of these are FileStream
(allows you to open a file directly for reading or
writing), StreamReader and
StreamWriter (used for reading and writing text,
one line at a time), and BinaryReader and
BinaryWriter (used for converting basic .NET data
types to binary data and back). Look these classes up in the MSN Help
for the traditional file-access techniques. Also, in the next lab,
you'll see a more advanced example that uses
FileStream to encrypt data in a file.
