FileStream.WriteAsync Method
Definition
Important
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Overloads
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(ReadOnlyMemory<Byte>, CancellationToken) |
Asynchronously writes a sequence of bytes from a memory region to the current file stream, advances the current position within this file stream by the number of bytes written, and monitors cancellation requests. |
WriteAsync(Byte[], Int32, Int32, CancellationToken)
- Source:
- FileStream.cs
- Source:
- FileStream.cs
- Source:
- FileStream.cs
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.
public:
override System::Threading::Tasks::Task ^ WriteAsync(cli::array <System::Byte> ^ buffer, int offset, int count, System::Threading::CancellationToken cancellationToken);
public override System.Threading.Tasks.Task WriteAsync (byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken);
[System.Runtime.InteropServices.ComVisible(false)]
public override System.Threading.Tasks.Task WriteAsync (byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken);
override this.WriteAsync : byte[] * int * int * System.Threading.CancellationToken -> System.Threading.Tasks.Task
[<System.Runtime.InteropServices.ComVisible(false)>]
override this.WriteAsync : byte[] * int * int * System.Threading.CancellationToken -> System.Threading.Tasks.Task
Public Overrides Function WriteAsync (buffer As Byte(), offset As Integer, count As Integer, cancellationToken As CancellationToken) As Task
Parameters
- 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.
Returns
A task that represents the asynchronous write operation.
- Attributes
Exceptions
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.
The cancellation token was canceled. This exception is stored into the returned task.
Examples
The following example shows how to write asynchronously to a file.
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 file operations without blocking the main thread. This performance consideration is particularly important in apps where a time-consuming stream operation can block the UI thread and make your app appear as if it isn't working.
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. If the handle to the file is disposed, the returned task contains the ObjectDisposedException exception in the Exception property.
This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by Write(Byte[], Int32, Int32).
See also
Applies to
WriteAsync(ReadOnlyMemory<Byte>, CancellationToken)
- Source:
- FileStream.cs
- Source:
- FileStream.cs
- Source:
- FileStream.cs
Asynchronously writes a sequence of bytes from a memory region to the current file stream, advances the current position within this file stream by the number of bytes written, and monitors cancellation requests.
public override System.Threading.Tasks.ValueTask WriteAsync (ReadOnlyMemory<byte> buffer, System.Threading.CancellationToken cancellationToken = default);
override this.WriteAsync : ReadOnlyMemory<byte> * System.Threading.CancellationToken -> System.Threading.Tasks.ValueTask
Public Overrides Function WriteAsync (buffer As ReadOnlyMemory(Of Byte), Optional cancellationToken As CancellationToken = Nothing) As ValueTask
Parameters
- buffer
- ReadOnlyMemory<Byte>
The region of memory to write data from.
- cancellationToken
- CancellationToken
The token to monitor for cancellation requests. The default value is None.
Returns
A task that represents the asynchronous write operation.
Exceptions
The cancellation token was canceled. This exception is stored into the returned task.
Remarks
The WriteAsync
method lets you perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in apps where a time-consuming stream operation can block the UI thread and make your app appear as if it isn't working.
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 TaskStatus.Canceled value for the Task.Status property.