StreamReader和StreamWriter类用于读取和写入数据到文本文件。这些类继承自抽象基类Stream，它支持读取和写入字节到文件流中。
StreamReader类
StreamReader类也从抽象基类TextReader继承，它代表读取一系列字符的读取器。下表介绍了StreamReader类的一些常用方法：
编号
方法
描述
1
Public Overrides Sub Close
它关闭StreamReader对象和底层流，并释放与阅读器相关的所有系统资源。
2
Public Overrides Function Peek As Integer
返回下一个可用字符，但不会消耗它。
3
Public Overrides Function Read As Integer
从输入流中读取下一个字符，并将字符位置前进一个字符。
示例
以下示例演示如何读取名为 test.txt 的文本文件。该文件读取：
Down the way where the nights are gay And the sun shines daily on the mountain top I took a trip on a sailing ship And when I reached Jamaica I made a stop
文件：fileProg.vb –
Imports System.IO Module fileProg Sub Main() Try ' Create an instance of StreamReader to read from a file. ' ' The using statement also closes the StreamReader. ' Using sr As StreamReader = New StreamReader("e:/jamaica.txt") Dim line As String ' Read and display lines from the file until the end of ' ' the file is reached. ' line = sr.ReadLine() While (line <> Nothing) Console.WriteLine(line) line = sr.ReadLine() End While End Using Catch e As Exception ' Let the user know what went wrong.' Console.WriteLine("The file could not be read:") Console.WriteLine(e.Message) End Try Console.ReadKey() End Sub End Module
编译和运行程序时显示的结果如下 –
F:filehandle>vbc fileProg.vb Microsoft (R) Visual Basic Compiler version 14.0.1038 for Visual Basic Copyright (c) Microsoft Corporation. All rights reserved. ... ... F:filehandle>fileProg.exe Down the way where the nights are gay And the sun shines daily on the mountain top I took a trip on a sailing ship And when I reached Jamaica I made a stop
StreamWriter类
StreamWriter类继承自抽象类TextWriter，它表示作者，可以编写一系列字符。
下表显示了该类最常用的一些方法：
编号
方法
描述
1
Public Overrides Sub Close
关闭当前StreamWriter对象和基础流。
2
Public Overrides Sub Flush
清除当前写入器的所有缓冲区，并将所有缓冲的数据写入基础流。
3
Public Overridable Sub Write (value As Boolean)
将布尔值的文本表示形式写入文本字符串或流(从TextWriter继承。)
4
Public Overrides Sub Write (value As Char)
将一个字符写入流中。
5
Public Overridable Sub Write (value As Decimal)
将十进制值的文本表示形式写入文本字符串或流。
6
Public Overridable Sub Write (value As Double)
将8字节浮点值的文本表示形式写入文本字符串或流。
7
Public Overridable Sub Write (value As Integer)
将4字节有符号整数的文本表示形式写入文本字符串或流。
8
Public Overrides Sub Write (value As String)
将一个字符串写入流。
9
Public Overridable Sub WriteLine
写一个行结束符到文本字符串或流。
以上列表并不详尽。 有关完整的方法列表，请访问Microsoft的文档
示例
以下示例演示如何使用StreamWriter类将文本数据写入文件中：
Imports System.IO Module writeFile Sub Main() Dim names As String() = New String() {"Hakou Ali", "Nacy Lee", "Amir Wong", "Marry Amlan"} Dim s As String Using sw As StreamWriter = New StreamWriter("names.txt") For Each s In names sw.WriteLine(s) Next s End Using ' Read and show each line from the file. ' Dim line As String Using sr As StreamReader = New StreamReader("names.txt") line = sr.ReadLine() While (line <> Nothing) Console.WriteLine(line) line = sr.ReadLine() End While End Using Console.ReadKey() End Sub End Module
执行上面示例代码，得到以下结果 –
F:filehandle>vbc writeFile.vb Microsoft (R) Visual Basic Compiler version 14.0.1038 for Visual Basic Copyright (c) Microsoft Corporation. All rights reserved. ...... F:filehandle>writeFile.exe Hakou Ali Nacy Lee Amir Wong Marry Amlan
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