IsolatedStorageFileStream.IsAsync 属性

定义

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。Gets a Boolean value indicating whether the IsolatedStorageFileStream object was opened asynchronously or synchronously.

public:
 virtual property bool IsAsync { bool get(); };
public override bool IsAsync { get; }
member this.IsAsync : bool
Public 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 falsetrue if the IsolatedStorageFileStream object supports asynchronous access; otherwise, false.

示例

下面的代码示例演示如何使用 IsAsync 属性来验证 IsolatedStorageFileStream 是否同步。The following code example demonstrates how you can use the IsAsync property to verify that an IsolatedStorageFileStream is synchronous. 有关此示例的完整上下文,请参阅 IsolatedStorageFileStream 概述。For the complete context of this example, see the IsolatedStorageFileStream overview.

double SetNewPrefsForUser()
{
   try
   {
      Byte inputChar;
      IsolatedStorageFile^ isoFile = IsolatedStorageFile::GetStore( static_cast<IsolatedStorageScope>(IsolatedStorageScope::User | IsolatedStorageScope::Assembly | IsolatedStorageScope::Domain), System::Security::Policy::Url::typeid, System::Security::Policy::Url::typeid );
      
      // If this is not a new user, archive the old preferences and 
      // overwrite them using the new preferences.
      if (  !this->NewPrefs )
      {
         if ( isoFile->GetDirectoryNames( "Archive" )->Length == 0 )
                     isoFile->CreateDirectory( "Archive" );
         else
         {
            
            // This is the stream to which data will be written.
            IsolatedStorageFileStream^ source = gcnew IsolatedStorageFileStream( this->userName,FileMode::OpenOrCreate,isoFile );
            
            // This is the stream from which data will be read.
            Console::WriteLine( "Is the source file readable?  {0}", (source->CanRead ? (String^)"true" : "false") );
            Console::WriteLine( "Creating new IsolatedStorageFileStream for Archive." );
            
            // Open or create a writable file.
            IsolatedStorageFileStream^ target = gcnew IsolatedStorageFileStream( String::Concat("Archive\\",this->userName),FileMode::OpenOrCreate,FileAccess::Write,FileShare::Write,isoFile );
            
            Console::WriteLine( "Is the target file writable? {0}", (target->CanWrite ? (String^)"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( (Byte)source->ReadByte() );
               }
               
               // Determine the size of the IsolatedStorageFileStream
               // by checking its Length property.
               Console::WriteLine( "Total Bytes Read: {0}", source->Length.ToString() );
               
            }
            
            // After you have read and written to the streams, close them.
            target->Close();
            source->Close();
         }
      }
      
      // Open or create a writable file, no larger than 10k
      IsolatedStorageFileStream^ isoStream = gcnew IsolatedStorageFileStream( this->userName,FileMode::OpenOrCreate,FileAccess::Write,FileShare::Write,10240,isoFile );
      
      isoStream->Position = 0; // Position to overwrite the old data.
      
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

不能创建异步 IsolatedStorageFileStream 对象,这与 FileStream不同。Asynchronous IsolatedStorageFileStream objects cannot be created, unlike FileStream. 但是,同步实例支持 BeginWriteBeginReadEndWriteEndRead 方法,但存在一些性能下降。However, the BeginWrite, BeginRead, EndWrite, and EndRead methods are supported on synchronous instances, with some performance penalties.

适用于

另请参阅