IsolatedStorageFileStream.IsAsync 属性
定义
重要
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获取一个布尔值，该值指示 IsolatedStorageFileStream 对象是异步打开的还是同步打开的。
public:
virtual property bool IsAsync { bool get(); };public override bool IsAsync { get; }member this.IsAsync : boolPublic Overrides ReadOnly Property IsAsync As Boolean属性值
如果 true 对象支持异步访问，则为 IsolatedStorageFileStream；否则为 false。
示例
下面的代码示例演示如何使用 IsAsync 属性来验证 是否 IsolatedStorageFileStream 是同步的。 有关此示例的完整上下文，请参阅 IsolatedStorageFileStream 概述。
public double SetNewPrefsForUser()
{
try
{
byte inputChar;
IsolatedStorageFile isoFile = IsolatedStorageFile.GetStore(IsolatedStorageScope.User |
IsolatedStorageScope.Assembly |
IsolatedStorageScope.Domain,
typeof(System.Security.Policy.Url),
typeof(System.Security.Policy.Url));
// If this is not a new user, archive the old preferences and
// overwrite them using the new preferences.
if (!this.myNewPrefs)
{
if (isoFile.GetDirectoryNames("Archive").Length == 0)
{
isoFile.CreateDirectory("Archive");
}
else
{
IsolatedStorageFileStream source =
new IsolatedStorageFileStream(this.userName, FileMode.OpenOrCreate,
isoFile);
// This is the stream from which data will be read.
Console.WriteLine("Is the source file readable? " + (source.CanRead ? "true" : "false"));
Console.WriteLine("Creating new IsolatedStorageFileStream for Archive.");
// Open or create a writable file.
IsolatedStorageFileStream target =
new IsolatedStorageFileStream("Archive\\ " + this.userName,
FileMode.OpenOrCreate,
FileAccess.Write,
FileShare.Write,
isoFile);
Console.WriteLine("Is the target file writable? " + (target.CanWrite ? "true" : "false"));
// Stream the old file to a new file in the Archive directory.
if (source.IsAsync && target.IsAsync)
{
// IsolatedStorageFileStreams cannot be asynchronous. However, you
// can use the asynchronous BeginRead and BeginWrite functions
// with some possible performance penalty.
Console.WriteLine("IsolatedStorageFileStreams cannot be asynchronous.");
}
else
{
Console.WriteLine("Writing data to the new file.");
while (source.Position < source.Length)
{
inputChar = (byte)source.ReadByte();
target.WriteByte(inputChar);
}
// Determine the size of the IsolatedStorageFileStream
// by checking its Length property.
Console.WriteLine("Total Bytes Read: " + source.Length);
}
// After you have read and written to the streams, close them.
target.Close();
source.Close();
}
}
// Open or create a writable file with a maximum size of 10K.
IsolatedStorageFileStream isoStream =
new IsolatedStorageFileStream(this.userName,
FileMode.OpenOrCreate,
FileAccess.Write,
FileShare.Write,
10240,
isoFile);
isoStream.Position = 0; // Position to overwrite the old data.
Public Function SetNewPrefsForUser() As Double
Try
Dim inputChar As Byte
Dim isoFile As IsolatedStorageFile = IsolatedStorageFile.GetStore(IsolatedStorageScope.User Or _
IsolatedStorageScope.Assembly Or IsolatedStorageScope.Domain, _
GetType(System.Security.Policy.Url), GetType(System.Security.Policy.Url))
' If this is not a new user, archive the old preferences and
' overwrite them using the new preferences.
If Not Me.myNewPrefs Then
If isoFile.GetDirectoryNames("Archive").Length = 0 Then
isoFile.CreateDirectory("Archive")
Else
Dim source As New IsolatedStorageFileStream(Me.userName, FileMode.OpenOrCreate, isoFile)
Dim canWrite, canRead As Boolean
' This is the stream from which data will be read.
If source.CanRead Then canRead = True Else canRead = False
Console.WriteLine("Is the source file readable? " & canRead)
Console.WriteLine("Creating new IsolatedStorageFileStream for Archive.")
' Open or create a writable file.
Dim target As New IsolatedStorageFileStream("Archive\ " & Me.userName, _
FileMode.OpenOrCreate, FileAccess.Write, FileShare.Write, isoFile)
' This is the stream to which data will be written.
If target.CanWrite Then canWrite = True Else canWrite = False
Console.WriteLine("Is the target file writable? " & canWrite)
target.SetLength(0) 'rewind the target file
' Stream the old file to a new file in the Archive directory.
If source.IsAsync And target.IsAsync Then
' IsolatedStorageFileStreams cannot be asynchronous. However, you
' can use the asynchronous BeginRead and BeginWrite functions
' with some possible performance penalty.
Console.WriteLine("IsolatedStorageFileStreams cannot be asynchronous.")
Else
Console.WriteLine("Writing data to the new file.")
While source.Position < source.Length
inputChar = CByte(source.ReadByte())
target.WriteByte(inputChar)
End While
' Determine the size of the IsolatedStorageFileStream
' by checking its Length property.
Console.WriteLine(("Total Bytes Read: " & source.Length))
End If
' After you have read and written to the streams, close them.
target.Close()
source.Close()
End If
End If
' Open or create a writable file with a maximum size of 10K.
Dim isoStream As New IsolatedStorageFileStream(Me.userName, FileMode.OpenOrCreate, _
FileAccess.Write, FileShare.Write, 10240, isoFile)
isoStream.SetLength(0) 'Position to overwrite the old data.
注解
无法创建异步 IsolatedStorageFileStream 对象，这与 不同 FileStream。 但是， BeginWrite同步实例支持 、 BeginRead、 EndWrite和 EndRead 方法，但存在一些性能损失。
