FileStream.CanWrite 属性
获取一个值，该值指示当前流是否支持写入。
**命名空间:**System.IO
**程序集:**mscorlib（在 mscorlib.dll 中）
语法
声明
Public Overrides ReadOnly Property CanWrite As Boolean
用法
Dim instance As FileStream
Dim value As Boolean
value = instance.CanWrite
public override bool CanWrite { get; }
public:
virtual property bool CanWrite {
bool get () override;
}
/** @property */
public boolean get_CanWrite ()
public override function get CanWrite () : boolean
属性值
如果流支持写入，则为 true；如果流已关闭或是通过只读访问方式打开的，则为 false。
备注
如果从 Stream 派生的类不支持写入，则对 SetLength、Write、BeginWrite 或 WriteByte 的调用将引发 NotSupportedException。
如果该流已关闭，此属性将返回 false。
示例
下面的示例使用 CanWrite 属性检查流是否支持写入操作。
Imports System
Imports System.IO
Public Class Test
Public Shared Sub Main()
Dim path As String = "c:\temp\MyTest.txt"
'Ensure that the file is readonly.
File.SetAttributes(path, File.GetAttributes(path) Or FileAttributes.ReadOnly)
'Create the file.
Dim fs As FileStream = New FileStream(path, FileMode.OpenOrCreate, FileAccess.Read)
If fs.CanWrite Then
Console.WriteLine("The stream connected to {0} is writable.", path)
Else
Console.WriteLine("The stream connected to {0} is not writable.", path)
End If
fs.Close()
End Sub
End Class
using System;
using System.IO;
using System.Text;
class Test
{
public static void Main()
{
string path = @"c:\temp\MyTest.txt";
// Ensure that the file is readonly.
File.SetAttributes(path, File.GetAttributes(path) | FileAttributes.ReadOnly);
//Create the file.
using (FileStream fs = new FileStream (path, FileMode.OpenOrCreate, FileAccess.Read))
{
if (fs.CanWrite)
{
Console.WriteLine("The stream for file {0} is writable.", path);
}
else
{
Console.WriteLine("The stream for file {0} is not writable.", path);
}
}
}
}
using namespace System;
using namespace System::IO;
using namespace System::Text;
int main()
{
String^ path = "c:\\temp\\MyTest.txt";
// Ensure that the file is readonly.
File::SetAttributes( path, static_cast<FileAttributes>(File::GetAttributes( path ) | FileAttributes::ReadOnly) );
//Create the file.
FileStream^ fs = gcnew FileStream( path,FileMode::OpenOrCreate,FileAccess::Read );
try
{
if ( fs->CanWrite )
{
Console::WriteLine( "The stream for file {0} is writable.", path );
}
else
{
Console::WriteLine( "The stream for file {0} is not writable.", path );
}
}
finally
{
if ( fs )
delete (IDisposable^)fs;
}
}
import System.*;
import System.IO.*;
import System.Text.*;
class Test
{
public static void main(String[] args)
{
String path = "c:\\temp\\MyTest.txt";
// Ensure that the file is readonly.
File.SetAttributes(path, File.GetAttributes(path) | FileAttributes.
ReadOnly);
//Create the file.
FileStream fs = new FileStream(path, FileMode.OpenOrCreate,
FileAccess.Read);
try {
if (fs.get_CanWrite()) {
Console.WriteLine("The stream for file {0} is writable.",
path);
}
else {
Console.WriteLine("The stream for file {0} is not writable.",
path);
}
}
finally {
fs.Dispose();
}
} //main
} //Test
下面是使用 CanWrite 属性的示例。此代码的输出为“MyFile.txt is writable.”。若要获取输出消息“MyFile.txt can be both written to and read from.”，请将 FileStream 构造函数中的 FileAccess 参数更改为 ReadWrite。
Imports System
Imports System.IO
Class TestRW
Public Shared Sub Main()
Dim fs As New FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write)
If fs.CanRead And fs.CanWrite Then
Console.WriteLine("MyFile.txt can be both written to and read from.")
ElseIf fs.CanWrite Then
Console.WriteLine("MyFile.txt is writable.")
End If
End Sub
End Class
using System;
using System.IO;
class TestRW
{
public static void Main(String[] args)
{
FileStream fs = new FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write);
if (fs.CanRead && fs.CanWrite)
{
Console.WriteLine("MyFile.txt can be both written to and read from.");
}
else if (fs.CanWrite)
{
Console.WriteLine("MyFile.txt is writable.");
}
}
}
using namespace System;
using namespace System::IO;
int main( void )
{
FileStream^ fs = gcnew FileStream( "MyFile.txt",FileMode::OpenOrCreate,FileAccess::Write );
if ( fs->CanRead && fs->CanWrite )
{
Console::WriteLine( "MyFile.txt can be both written to and read from." );
}
else
{
Console::WriteLine( "MyFile.txt is writable." );
}
return 0;
}
import System;
import System.IO;
class TestRW
{
public static function Main() : void
{
var fs : FileStream = new FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Write);
if (fs.CanRead && fs.CanWrite)
Console.WriteLine("MyFile.txt can be both written to and read from.");
else if (fs.CanWrite)
Console.WriteLine("MyFile.txt is writable.");
}
}
TestRW.Main();
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、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
.NET Compact Framework
受以下版本支持：2.0、1.0
请参见
参考
FileStream 类
FileStream 成员
System.IO 命名空间