The System.IO Namespace

王朝asp·作者佚名  2006-01-10
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The System.IO Namespace

The System.IO namespace contains classes that allow you to read and write

files on disk. File operations can be performed either synchronously or

asynchronously. In order to read and write data, you'll work with the base

Stream class, which provides a generic technique to access any data without

regard to the underlying platform on which the data resides. Streams can

support any combination of reading, writing, and seeking (that is,

modifying the current position within a stream). Table 4.3 presents a list

of some of the more commonly used classes from the System.IO namespace.

Table 4.3. System.IO Classes Class Description

File The File class provides shared methods that allow you to perform

actions on physical files on disk.

StreamReader The StreamReader class allows you to open and read

information from a file on disk.

StreamWriter The StreamWriter class allows you to write to files on disk.

A File object represents a physical file and allows you to perform actions

such as copying and deleting files. The File class provides Exists, Open,

OpenRead, OpenText, and OpenWrite methods to allow you to perform file I/O.

These methods of the File class are defined as Shared, which means you do

not need to create an instance of a File class to use them. You will learn

more about shared methods in Chapter 7, "Working with ASP.NET and VB .NET."

The two classes you will use most often from the System.IO namespace are

StreamReader and StreamWriter, and you'll learn about these two classes in

the following example.

A System.IO Example

The code in Listing 4.1, located under the "IO Classes" hyperlink on

Main.aspx, uses a StreamWriter object to create a new text file on disk.

The code uses the shared Exists method of the File class to determine

whether a file exists on disk. (Although it's perfectly reasonable, and

possible, for code to overwrite an existing file, this example doesn't do

that.) If the file does not exist, the example creates a new StreamWriter

object by invoking the CreateText shared method of the File class. This

method creates the file and returns a StreamWriter object that can be used

to write information into the file. Once the file is opened, the example

uses the WriteLine method to place text into the file on disk. When done

using the file, the example closes it to release the handle back to the

operating system. Here's the code:

Listing 4.1 Writing to a File Using the Stream and File Objects

Imports System.IO

Private Sub WriteFile()

Dim strName As String

Dim sw As StreamWriter

strName = Server.MapPath("Test.txt")

If File.Exists(strName) Then

lblError.Text = "File Already Exists"

Else

sw = File.CreateText(strName)

sw.WriteLine("The current Time is: " & Now())

sw.Close()

End If

End Sub

 
 
 
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