FileStream.Lock 方法
允许读取访问的同时防止其他进程更改 FileStream。
**命名空间:**System.IO
**程序集:**mscorlib（在 mscorlib.dll 中）
语法
声明
Public Overridable Sub Lock ( _
position As Long, _
length As Long _
)
用法
Dim instance As FileStream
Dim position As Long
Dim length As Long
instance.Lock(position, length)
public virtual void Lock (
long position,
long length
)
public:
virtual void Lock (
long long position,
long long length
)
public void Lock (
long position,
long length
)
public function Lock (
position : long,
length : long
)
参数
- position
要锁定的范围的开始处。此参数的值必须大于或等于零 (0)。
- length
要锁定的范围。
异常
| 异常类型 | 条件 |
|---|---|
position 或 length 为负。 |
|
文件被关闭。 |
|
由于另一个进程已锁定文件的部分内容，因此该进程无法访问该文件。 |
备注
下表列出了其他典型或相关的 I/O 任务的示例。
若要执行此操作... |
请参见本主题中的示例... |
|---|---|
创建文本文件。 |
|
写入文本文件。 |
|
读取文本文件。 |
|
向文件中追加文本。 |
|
重命名或移动文件。 |
|
复制文件。 |
|
获取目录的大小。 |
|
获取文件属性。 |
|
设置文件属性。 |
|
创建子目录。 |
|
读取二进制文件。 |
|
写入二进制文件。 |
|
查看目录中的文件。 |
|
按大小对目录中的文件排序。 |
示例
下面的代码示例阐释了如何通过相应地锁定一个文件的某个部分，使其他进程即使对该文件有读/写访问权限也无法访问该文件的这一部分。同时在不同的命令窗口中运行该程序，研究如何使用不同的控制台输入选项。
Imports Microsoft.VisualBasic
Imports System
Imports System.IO
Imports System.Text
Public Class FStreamLock
Shared Sub Main()
Dim uniEncoding As New UnicodeEncoding()
Dim lastRecordText As String = _
"The last processed record number was: "
Dim textLength As Integer = _
uniEncoding.GetByteCount(lastRecordText)
Dim recordNumber As Integer = 13
Dim byteCount As Integer = _
uniEncoding.GetByteCount(recordNumber.ToString())
Dim tempString As String
Dim aFileStream As New FileStream( _
"Test#@@#.dat", FileMode.OpenOrCreate, _
FileAccess.ReadWrite, FileShare.ReadWrite)
Try
' Write the original file data.
If aFileStream.Length = 0 Then
tempString = _
lastRecordText + recordNumber.ToString()
aFileStream.Write(uniEncoding.GetBytes(tempString), _
0, uniEncoding.GetByteCount(tempString))
End If
' Allow the user to choose the operation.
Dim consoleInput As Char = "R"C
Dim readText(CInt(aFileStream.Length)) As Byte
While consoleInput <> "X"C
Console.Write(vbcrLf & _
"Enter 'R' to read, 'W' to write, 'L' to " & _
"lock, 'U' to unlock, anything else to exit: ")
tempString = Console.ReadLine()
If tempString.Length = 0 Then
Exit While
End If
consoleInput = Char.ToUpper(tempString.Chars(0))
Select consoleInput
' Read data from the file and
' write it to the console.
Case "R"C
Try
aFileStream.Seek(0, SeekOrigin.Begin)
aFileStream.Read( _
readText, 0, CInt(aFileStream.Length))
tempString = New String( _
uniEncoding.GetChars( _
readText, 0, readText.Length))
Console.WriteLine(tempString)
recordNumber = Integer.Parse( _
tempString.Substring( _
tempString.IndexOf(":"C) + 2))
' Catch the IOException generated if the
' specified part of the file is locked.
Catch ex As IOException
Console.WriteLine("{0}: The read " & _
"operation could not be performed " & _
"because the specified part of the" & _
" file is locked.", _
ex.GetType().Name)
End Try
Exit Select
' Update the file.
Case "W"C
Try
aFileStream.Seek(textLength, _
SeekOrigin.Begin)
aFileStream.Read( _
readText, textLength - 1, byteCount)
tempString = New String( _
uniEncoding.GetChars( _
readText, textLength - 1, byteCount))
recordNumber = _
Integer.Parse(tempString) + 1
aFileStream.Seek( _
textLength, SeekOrigin.Begin)
aFileStream.Write(uniEncoding.GetBytes( _
recordNumber.ToString()), 0, byteCount)
aFileStream.Flush()
Console.WriteLine( _
"Record has been updated.")
' Catch the IOException generated if the
' specified part of the file is locked.
Catch ex As IOException
Console.WriteLine( _
"{0}: The write operation could " & _
"not be performed because the " & _
"specified part of the file is " & _
"locked.", ex.GetType().Name)
End Try
Exit Select
' Lock the specified part of the file.
Case "L"C
Try
aFileStream.Lock(textLength - 1, byteCount)
Console.WriteLine("The specified part " & _
"of file has been locked.")
Catch ex As IOException
Console.WriteLine( _
"{0}: The specified part of file " & _
"is already locked.", _
ex.GetType().Name)
End Try
Exit Select
' Unlock the specified part of the file.
Case "U"C
Try
aFileStream.Unlock( _
textLength - 1, byteCount)
Console.WriteLine("The specified part " & _
"of file has been unlocked.")
Catch ex As IOException
Console.WriteLine( _
"{0}: The specified part of file " & _
"is not locked by the current " & _
"process.", ex.GetType().Name)
End Try
Exit Select
' Exit the program.
Case Else
consoleInput = "X"C
Exit While
End Select
End While
Finally
aFileStream.Close()
End Try
End Sub
End Class
using System;
using System.IO;
using System.Text;
class FStreamLock
{
static void Main()
{
UnicodeEncoding uniEncoding = new UnicodeEncoding();
string lastRecordText =
"The last processed record number was: ";
int textLength = uniEncoding.GetByteCount(lastRecordText);
int recordNumber = 13;
int byteCount =
uniEncoding.GetByteCount(recordNumber.ToString());
string tempString;
using(FileStream fileStream = new FileStream(
"Test#@@#.dat", FileMode.OpenOrCreate,
FileAccess.ReadWrite, FileShare.ReadWrite))
{
// Write the original file data.
if(fileStream.Length == 0)
{
tempString =
lastRecordText + recordNumber.ToString();
fileStream.Write(uniEncoding.GetBytes(tempString),
0, uniEncoding.GetByteCount(tempString));
}
// Allow the user to choose the operation.
char consoleInput = 'R';
byte[] readText = new byte[fileStream.Length];
while(consoleInput != 'X')
{
Console.Write(
"\nEnter 'R' to read, 'W' to write, 'L' to " +
"lock, 'U' to unlock, anything else to exit: ");
if((tempString = Console.ReadLine()).Length == 0)
{
break;
}
consoleInput = char.ToUpper(tempString[0]);
switch(consoleInput)
{
// Read data from the file and
// write it to the console.
case 'R':
try
{
fileStream.Seek(0, SeekOrigin.Begin);
fileStream.Read(
readText, 0, (int)fileStream.Length);
tempString = new String(
uniEncoding.GetChars(
readText, 0, readText.Length));
Console.WriteLine(tempString);
recordNumber = int.Parse(
tempString.Substring(
tempString.IndexOf(':') + 2));
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch(IOException e)
{
Console.WriteLine("{0}: The read " +
"operation could not be performed " +
"because the specified part of the " +
"file is locked.",
e.GetType().Name);
}
break;
// Update the file.
case 'W':
try
{
fileStream.Seek(textLength,
SeekOrigin.Begin);
fileStream.Read(
readText, textLength - 1, byteCount);
tempString = new String(
uniEncoding.GetChars(
readText, textLength - 1, byteCount));
recordNumber = int.Parse(tempString) + 1;
fileStream.Seek(
textLength, SeekOrigin.Begin);
fileStream.Write(uniEncoding.GetBytes(
recordNumber.ToString()),
0, byteCount);
fileStream.Flush();
Console.WriteLine(
"Record has been updated.");
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch(IOException e)
{
Console.WriteLine(
"{0}: The write operation could not " +
"be performed because the specified " +
"part of the file is locked.",
e.GetType().Name);
}
break;
// Lock the specified part of the file.
case 'L':
try
{
fileStream.Lock(textLength - 1, byteCount);
Console.WriteLine("The specified part " +
"of file has been locked.");
}
catch(IOException e)
{
Console.WriteLine(
"{0}: The specified part of file is" +
" already locked.", e.GetType().Name);
}
break;
// Unlock the specified part of the file.
case 'U':
try
{
fileStream.Unlock(
textLength - 1, byteCount);
Console.WriteLine("The specified part " +
"of file has been unlocked.");
}
catch(IOException e)
{
Console.WriteLine(
"{0}: The specified part of file is " +
"not locked by the current process.",
e.GetType().Name);
}
break;
// Exit the program.
default:
consoleInput = 'X';
break;
}
}
}
}
}
using namespace System;
using namespace System::IO;
using namespace System::Text;
int main()
{
UnicodeEncoding^ uniEncoding = gcnew UnicodeEncoding;
String^ lastRecordText = "The last processed record number was: ";
int textLength = uniEncoding->GetByteCount( lastRecordText );
int recordNumber = 13;
int byteCount = uniEncoding->GetByteCount( recordNumber.ToString() );
String^ tempString;
FileStream^ fileStream = gcnew FileStream( "Test#@@#.dat",FileMode::OpenOrCreate,FileAccess::ReadWrite,FileShare::ReadWrite );
try
{
// Write the original file data.
if ( fileStream->Length == 0 )
{
tempString = String::Concat( lastRecordText, recordNumber.ToString() );
fileStream->Write( uniEncoding->GetBytes( tempString ), 0, uniEncoding->GetByteCount( tempString ) );
}
// Allow the user to choose the operation.
Char consoleInput = 'R';
array<Byte>^readText = gcnew array<Byte>(fileStream->Length);
while ( consoleInput != 'X' )
{
Console::Write( "\nEnter 'R' to read, 'W' to write, 'L' to "
"lock, 'U' to unlock, anything else to exit: " );
if ( (tempString = Console::ReadLine())->Length == 0 )
{
break;
}
consoleInput = Char::ToUpper( tempString[0] );
switch ( consoleInput )
{
case 'R':
try
{
fileStream->Seek( 0, SeekOrigin::Begin );
fileStream->Read( readText, 0, (int)fileStream->Length );
tempString = gcnew String( uniEncoding->GetChars( readText, 0, readText->Length ) );
Console::WriteLine( tempString );
recordNumber = Int32::Parse( tempString->Substring( tempString->IndexOf( ':' ) + 2 ) );
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch ( IOException^ e )
{
Console::WriteLine( "{0}: The read "
"operation could not be performed "
"because the specified part of the "
"file is locked.", e->GetType()->Name );
}
break;
// Update the file.
case 'W':
try
{
fileStream->Seek( textLength, SeekOrigin::Begin );
fileStream->Read( readText, textLength - 1, byteCount );
tempString = gcnew String( uniEncoding->GetChars( readText, textLength - 1, byteCount ) );
recordNumber = Int32::Parse( tempString ) + 1;
fileStream->Seek( textLength, SeekOrigin::Begin );
fileStream->Write( uniEncoding->GetBytes( recordNumber.ToString() ), 0, byteCount );
fileStream->Flush();
Console::WriteLine( "Record has been updated." );
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch ( IOException^ e )
{
Console::WriteLine( "{0}: The write operation could not "
"be performed because the specified "
"part of the file is locked.", e->GetType()->Name );
}
break;
// Lock the specified part of the file.
case 'L':
try
{
fileStream->Lock( textLength - 1, byteCount );
Console::WriteLine( "The specified part "
"of file has been locked." );
}
catch ( IOException^ e )
{
Console::WriteLine( "{0}: The specified part of file is"
" already locked.", e->GetType()->Name );
}
break;
// Unlock the specified part of the file.
case 'U':
try
{
fileStream->Unlock( textLength - 1, byteCount );
Console::WriteLine( "The specified part "
"of file has been unlocked." );
}
catch ( IOException^ e )
{
Console::WriteLine( "{0}: The specified part of file is "
"not locked by the current process.", e->GetType()->Name );
}
break;
default:
// Exit the program.
consoleInput = 'X';
break;
}
}
}
finally
{
fileStream->Close();
}
}
import System.*;
import System.IO.*;
import System.Text.*;
class FStreamLock
{
public static void main(String[] args)
{
UnicodeEncoding uniEncoding = new UnicodeEncoding();
String lastRecordText = "The last processed record number was: ";
int textLength = uniEncoding.GetByteCount(lastRecordText);
int recordNumber = 13;
int byteCount = uniEncoding.GetByteCount(
(new Integer(recordNumber)).ToString());
String tempString;
FileStream fileStream = new FileStream
("Test#@@#.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite,
FileShare.ReadWrite);
try {
// Write the original file data.
if ( fileStream.get_Length() == 0 ) {
tempString = lastRecordText +(
new Integer( recordNumber)).ToString();
fileStream.Write(uniEncoding.GetBytes(tempString),
0, uniEncoding.GetByteCount(tempString));
}
// Allow the user to choose the operation.
char consoleInput = 'R';
ubyte readText[] = new ubyte[(int) fileStream.get_Length() ];
while((consoleInput != 'X')) {
Console.Write(("\nEnter 'R' to read,'W' to write, 'L' to "
+ "lock, 'U' to unlock, anything else to exit: "));
if (((String)(tempString =
Console.ReadLine())).get_Length() == 0) {
break ;
}
consoleInput = Char.ToUpper( tempString.get_Chars(0));
switch(consoleInput) {
// Read data from the file and
// write it to the console.
case 'R' :
try {
fileStream.Seek(0, SeekOrigin.Begin);
fileStream.Read(readText, 0,
(int)(fileStream.get_Length()));
tempString = new String(
uniEncoding.GetChars(readText,
0, readText.length ));
Console.WriteLine(tempString);
recordNumber = Int32.Parse(
tempString.Substring(
tempString.IndexOf(':') + 2));
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch(IOException e) {
Console.WriteLine("{0}: The read "
+ "operation could not be performed "
+ "because the specified part of the "
+ "file is locked.", e.GetType().get_Name());
}
break;
// Update the file.
case 'W' :
try {
fileStream.Seek(textLength, SeekOrigin.Begin);
fileStream.Read(readText,
textLength - 1, byteCount);
tempString = new String(uniEncoding.GetChars(
readText, textLength - 1, byteCount));
recordNumber = Int32.Parse(tempString)+1;
fileStream.Seek(textLength, SeekOrigin.Begin);
fileStream.Write(uniEncoding.GetBytes(
(new Integer( recordNumber)).ToString()),
0, byteCount);
fileStream.Flush();
Console.WriteLine("Record has been updated.");
}
// Catch the IOException generated if the
// specified part of the file is locked.
catch(IOException e) {
Console.WriteLine(
"{0}: The write operation could not "
+ "be performed because the specified "
+ "part of the file is locked.",
e.GetType().get_Name());
}
break;
// Lock the specified part of the file.
case 'L' :
try {
fileStream.Lock(textLength - 1, byteCount);
Console.WriteLine(("The specified part "
+ "of file has been locked."));
}
catch(IOException e) {
Console.WriteLine
("{0}: The specified part of file is"
+ " already locked.", e.GetType().get_Name());
}
break;
// Unlock the specified part of the file.
case 'U' :
try {
fileStream.Unlock(textLength - 1, byteCount);
Console.WriteLine(("The specified part "
+ "of file has been unlocked."));
}
catch(IOException e) {
Console.WriteLine(
"{0}: The specified part of file is "
+ "not locked by the current process.",
e.GetType().get_Name());
}
break;
// Exit the program.
default :
// Exit the program.
consoleInput = 'X';
break;
}
}
}
finally {
fileStream.Dispose();
}
} //main
} //FStreamLock
平台
Windows 98、Windows 2000 SP4、Windows Millennium Edition、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
请参见
参考
FileStream 类
FileStream 成员
System.IO 命名空间