FileStream.IsAsync-Eigenschaft

Ruft einen Wert ab, der angibt, ob FileStream asynchron oder synchron geöffnet wurde.

Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Overridable ReadOnly Property IsAsync As Boolean
'Usage
Dim instance As FileStream
Dim value As Boolean

value = instance.IsAsync

public virtual bool IsAsync { get; }

public:
virtual property bool IsAsync {
    bool get ();
}

/** @property */
public boolean get_IsAsync ()

public function get IsAsync () : boolean

Eigenschaftenwert

true, wenn FileStream asynchron geöffnet wurde, andernfalls false.

Hinweise

Die IsAsync-Eigenschaft erkennt, ob das FileStream-Handle asynchron geöffnet wurde. Somit kann die Handle-Eigenschaft ordnungsgemäß vom Code verwendet werden. Bei Win32 wurde das Handle für die überlappende E/A geöffnet, wenn IsAsync auf True festgelegt wurde, und es erfordert daher andere Parameter für ReadFile und WriteFile.

Hinweis zu Windows 98, Windows Millennium Edition: Diese Betriebssysteme unterstützen keine asynchrone E/A. Wenn Code für diese Plattformen das asynchrone Öffnen von Dateien anfordert, öffnet die Common Language Runtime diese stattdessen synchron.

Beispiel

Dieses Codebeispiel ist Teil eines umfangreicheren Beispiels für den FileStream(String,FileMode,FileAccess,FileShare,Int32,Boolean)-Konstruktor.

Shared Sub Main()

    ' Create a synchronization object that gets 
    ' signaled when verification is complete.
    Dim manualEvent As New ManualResetEvent(False)

    ' Create random data to write to the file.
    Dim writeArray(100000) As Byte
    Dim randomGenerator As New Random()
    randomGenerator.NextBytes(writeArray)

    Dim fStream As New FileStream("Test#@@#.dat", _
        FileMode.Create, FileAccess.ReadWrite, _
        FileShare.None, 4096, True)

    ' Check that the FileStream was opened asynchronously.
    If fStream.IsAsync = True
        Console.WriteLine("fStream was opened asynchronously.")
    Else
        Console.WriteLine("fStream was not opened asynchronously.")
    End If

    ' Asynchronously write to the file.
    Dim asyncResult As IAsyncResult = fStream.BeginWrite( _
        writeArray, 0, writeArray.Length, _
        AddressOf EndWriteCallback , _
        New State(fStream, writeArray, manualEvent))

    ' Concurrently do other work and then wait
    ' for the data to be written and verified.
    manualEvent.WaitOne(5000, False)
End Sub

static void Main()
{
    // Create a synchronization object that gets 
    // signaled when verification is complete.
    ManualResetEvent manualEvent = new ManualResetEvent(false);

    // Create random data to write to the file.
    byte[] writeArray = new byte[100000];
    new Random().NextBytes(writeArray);

    FileStream fStream = 
        new FileStream("Test#@@#.dat", FileMode.Create, 
        FileAccess.ReadWrite, FileShare.None, 4096, true);

    // Check that the FileStream was opened asynchronously.
    Console.WriteLine("fStream was {0}opened asynchronously.",
        fStream.IsAsync ? "" : "not ");

    // Asynchronously write to the file.
    IAsyncResult asyncResult = fStream.BeginWrite(
        writeArray, 0, writeArray.Length, 
        new AsyncCallback(EndWriteCallback), 
        new State(fStream, writeArray, manualEvent));

    // Concurrently do other work and then wait 
    // for the data to be written and verified.
    manualEvent.WaitOne(5000, false);
}

int main()
{
   
   // Create a synchronization object that gets 
   // signaled when verification is complete.
   ManualResetEvent^ manualEvent = gcnew ManualResetEvent( false );
   
   // Create the data to write to the file.
   array<Byte>^writeArray = gcnew array<Byte>(100000);
   (gcnew Random)->NextBytes( writeArray );
   FileStream^ fStream = gcnew FileStream(  "Test#@@#.dat",FileMode::Create,FileAccess::ReadWrite,FileShare::None,4096,true );
   
   // Check that the FileStream was opened asynchronously.
   Console::WriteLine( "fStream was {0}opened asynchronously.", fStream->IsAsync ? (String^)"" : "not " );
   
   // Asynchronously write to the file.
   IAsyncResult^ asyncResult = fStream->BeginWrite( writeArray, 0, writeArray->Length, gcnew AsyncCallback( &FStream::EndWriteCallback ), gcnew State( fStream,writeArray,manualEvent ) );
   
   // Concurrently do other work and then wait 
   // for the data to be written and verified.
   manualEvent->WaitOne( 5000, false );
}

public static void main(String[] args)
{
    // Create a synchronization object that gets 
    // signaled when verification is complete.
    ManualResetEvent manualEvent = new ManualResetEvent(false);

    // Create random data to write to the file.
    ubyte writeArray[] = new ubyte[100000];
    new Random().NextBytes(writeArray);

    FileStream fStream =  new FileStream("Test#@@#.dat", FileMode.Create,
        FileAccess.ReadWrite, FileShare.None, 4096, true);

    // Check that the FileStream was opened asynchronously.
    Console.WriteLine("fStream was {0}opened asynchronously.",
        (fStream.get_IsAsync()) ? "" : "not ");
    FStream classfStream = new FStream();

    // Asynchronously write to the file.
    IAsyncResult asyncResult = fStream.BeginWrite(writeArray, 0,
        writeArray.length, new AsyncCallback(EndWriteCallback),
        classfStream.new State(fStream, writeArray, manualEvent));

    // Concurrently do other work and then wait 
    // for the data to be written and verified.
    manualEvent.WaitOne(5000, false);
} //main

Plattformen

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.

Versionsinformationen

.NET Framework

Unterstützt in: 2.0, 1.1, 1.0

.NET Compact Framework

Unterstützt in: 2.0, 1.0

Siehe auch

Referenz

FileStream-Klasse
FileStream-Member
System.IO-Namespace

Weitere Ressourcen

Datei- und Stream-E/A
Gewusst wie: Lesen aus einer Textdatei
Gewusst wie: Schreiben von Text in eine Datei