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Ruft einen booleschen Wert ab, der anzeigt, ob das IsolatedStorageFileStream-Objekt asynchron oder synchron geöffnet wurde.
Namespace: System.IO.IsolatedStorage
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Overrides ReadOnly Property IsAsync As Boolean
'Usage
Dim instance As IsolatedStorageFileStream
Dim value As Boolean
value = instance.IsAsync
public override bool IsAsync { get; }
public:
virtual property bool IsAsync {
bool get () override;
}
/** @property */
public boolean get_IsAsync ()
public override function get IsAsync () : boolean
Eigenschaftenwert
true, wenn das IsolatedStorageFileStream-Objekt den asynchronen Zugriff unterstützt, andernfalls false.
Hinweise
Im Gegensatz zu FileStream ist das Erstellen asynchronerIsolatedStorageFileStream-Objekte nicht möglich. Die Methoden BeginWrite, BeginRead, EndWrite und EndRead werden jedoch für synchrone Instanzen unterstützt, wenn auch mit Leistungseinbußen.
Beispiel
Das folgende Codebeispiel veranschaulicht, wie Sie mit der IsAsync-Eigenschaft überprüfen können, ob ein IsolatedStorageFileStream synchron ist. Den vollständigen Kontext dieses Beispiels finden Sie in der Übersicht zu IsolatedStorageFileStream.
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.
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.
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.
Plattformen
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 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
Siehe auch
Referenz
IsolatedStorageFileStream-Klasse
IsolatedStorageFileStream-Member
System.IO.IsolatedStorage-Namespace
FileStream-Klasse