ReadAsync

Asynchronously reads a sequence of bytes from the current stream, advances the position within the stream by the number of bytes read, and monitors cancellation requests.

Syntax

public override System.Threading.Tasks.Task<int> ReadAsync (byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken)

Parameters

buffer
The buffer to write the data into.
offset
The byte offset in buffer at which to begin writing data from the stream.
count
The maximum number of bytes to read.
cancellationToken
The token to monitor for cancellation requests.

Returns

A task that represents the asynchronous read operation. The value of the TResult parameter contains the total number of bytes read into the buffer. The result value can be less than the number of bytes requested if the number of bytes currently available is less than the requested number, or it can be 0 (zero) if the end of the stream has been reached.

Remarks

The FileStream.ReadAsync(Byte[], int, int, System.Threading.CancellationToken) method enables you to perform resource-intensive file operations without blocking the main thread. This performance consideration is particularly important in a win8_appname_long app or desktop_appname 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 FileStream.CanRead property to determine whether the current instance supports reading.

If the operation is canceled before it completes, the returned task contains the System.Threading.Tasks.TaskStatus.Canceled value for the System.Threading.Tasks.Task.Status property. If the handle to the file is disposed, the returned task contains the ObjectDisposedException exception in the System.Threading.Tasks.Task.Exception property.

Requirements

Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 4.0.0.0