Stream.WriteAsync
Method
Definition
Overloads
| WriteAsync(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. |
| WriteAsync(Byte[], Int32, Int32, CancellationToken) |
Asynchronously writes a sequence of bytes to the current stream, advances the current position within this stream by the number of bytes written, and monitors cancellation requests. |
WriteAsync(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.
[System.Runtime.InteropServices.ComVisible(false)]
public System.Threading.Tasks.Task WriteAsync (byte[] buffer, int offset, int count);
- buffer
- Byte[]
The buffer to write data from.
- offset
- Int32
The zero-based byte offset in buffer from which to begin copying bytes to the stream.
- count
- Int32
The maximum number of bytes to write.
A task that represents the asynchronous write operation.
buffer is null.
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.
Examples
The following example shows how to write asynchronously to a file. The example uses the FileStream class, which derives from the Stream class.
using System;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.IO;
namespace WpfApplication1
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private async void Button_Click(object sender, RoutedEventArgs e)
{
UnicodeEncoding uniencoding = new UnicodeEncoding();
string filename = @"c:\Users\exampleuser\Documents\userinputlog.txt";
byte[] result = uniencoding.GetBytes(UserInput.Text);
using (FileStream SourceStream = File.Open(filename, FileMode.OpenOrCreate))
{
SourceStream.Seek(0, SeekOrigin.End);
await SourceStream.WriteAsync(result, 0, result.Length);
}
}
}
}
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
Remarks
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 8.x 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.
WriteAsync(Byte[], Int32, Int32, CancellationToken)
Asynchronously writes a sequence of bytes to the current stream, advances the current position within this stream by the number of bytes written, and monitors cancellation requests.
[System.Runtime.InteropServices.ComVisible(false)]
public virtual System.Threading.Tasks.Task WriteAsync (byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken);
- buffer
- Byte[]
The buffer to write data from.
- offset
- Int32
The zero-based byte offset in buffer from which to begin copying bytes to the stream.
- count
- Int32
The maximum number of bytes to write.
- cancellationToken
- CancellationToken
The token to monitor for cancellation requests. The default value is None.
A task that represents the asynchronous write operation.
buffer is null.
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.
Remarks
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 8.x 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.
If the operation is canceled before it completes, the returned task contains the Canceled value for the Status property.
For an example, see the WriteAsync(Byte[], Int32, Int32) overload.