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