Stream.WriteAsync Method (Byte(), Int32, Int32)
Asynchronously writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
Assembly: mscorlib (in mscorlib.dll)
'Declaration <ComVisibleAttribute(False)> _ <HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _ Public Function WriteAsync ( _ buffer As Byte(), _ offset As Integer, _ count As Integer _ ) As Task
- Type: System.Byte()
The buffer to write data from.
- Type: System.Int32
The zero-based byte offset in buffer from which to begin copying bytes to the stream.
- Type: System.Int32
The maximum number of bytes to write.
Return ValueType: System.Threading.Tasks.Task
A task that represents the asynchronous write operation.
buffer is Nothing.
offset or count is negative.
The sum of offset and count is larger than the buffer length.
The stream does not support writing.
The stream has been disposed.
The stream is currently in use by a previous write operation.
The WriteAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows Store app or desktop app where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working. The async methods are used in conjunction with the async and await keywords in Visual Basic and C#.
Use the CanWrite property to determine whether the current instance supports writing.
The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.
Imports System.IO Imports System.Text Class MainWindow Private Async Sub Button_Click(sender As Object, e As RoutedEventArgs) Dim uniencoding As UnicodeEncoding = New UnicodeEncoding() Dim filename As String = "c:\Users\exampleuser\Documents\userinputlog.txt" Dim result As Byte() = uniencoding.GetBytes(UserInput.Text) Using SourceStream As FileStream = File.Open(filename, FileMode.OpenOrCreate) SourceStream.Seek(0, SeekOrigin.End) Await SourceStream.WriteAsync(result, 0, result.Length) End Using End Sub End Class
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)