VB.Net 从文本文件读取和写入
VB.Net 文件处理StreamReader和StreamWriter类用于从文本文件读取和写入数据。 这些类继承自抽象基类Stream，它支持将字节读取和写入文件流。
StreamReader类
StreamReader类还继承自抽象基类TextReader，它代表用于阅读一系列字符的读者。 下表描述了StreamReader类的一些常用方法：| S.N | 方法名称和用途 |
|---|---|
| 1 |
Public Overrides Sub Close It closes the StreamReader object and the underlying stream and releases any system resources associated with the reader. 它关闭StreamReader对象和基础流，并释放与读取器相关联的任何系统资源。 |
| 2 |
Public Overrides Function Peek As Integer Returns the next available character but does not consume it. 返回下一个可用字符，但不使用它。 |
| 3 |
Public Overrides Function Read As Integer Reads the next character from the input stream and advances the character position by one character. 从输入流中读取下一个字符，并将字符位置前移一个字符。 |
示例：
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
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
StreamWriter类
StreamWriter类继承自抽象类TextWriter，表示一个写入器，它可以写一系列字符。下表显示了此类最常用的一些方法：
| S.N | 方法名称和用途 |
|---|---|
| 1 |
Public Overrides Sub Close Closes the current StreamWriter object and the underlying stream. 关闭当前StreamWriter对象和基础流。 |
| 2 |
Public Overrides Sub Flush Clears all buffers for the current writer and causes any buffered data to be written to the underlying stream. 清除当前写入程序的所有缓冲区，并使任何缓冲的数据写入基础流。 |
| 3 |
Public Overridable Sub Write (value As Boolean) Writes the text representation of a Boolean value to the text string or stream. (Inherited from TextWriter.) 将布尔值的文本表示写入文本字符串或流。（从TextWriter继承。） |
| 4 |
Public Overrides Sub Write (value As Char) Writes a character to the stream. 将字符写入流。 |
| 5 |
Public Overridable Sub Write (value As Decimal) Writes the text representation of a decimal value to the text string or stream. 将十进制值的文本表示写入文本字符串或流。 |
| 6 |
Public Overridable Sub Write (value As Double) Writes the text representation of an 8-byte floating-point value to the text string or stream. 将8字节浮点值的文本表示写入文本字符串或流。 |
| 7 |
Public Overridable Sub Write (value As Integer) Writes the text representation of a 4-byte signed integer to the text string or stream. 将4字节有符号整数的文本表示写入文本字符串或流。 |
| 8 |
Public Overrides Sub Write (value As String) Writes a string to the stream. 将字符串写入流。 |
| 9 |
Public Overridable Sub WriteLine Writes a line terminator to the text string or stream. 将行终止符写入文本字符串或流。 |
示例：
以下示例演示使用StreamWriter类将文本数据写入文件：Imports System.IO
Module fileProg
Sub Main()
Dim names As String() = New String() {"Zara Ali", _
"Nuha Ali", "Amir Sohel", "M 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
Zara Ali
Nuha Ali
Amir Sohel
M Amlan
