Stream.ReadAsync Method (array<Byte>[]()[], Int32, Int32)

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

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

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


Public Function ReadAsync ( _
    buffer As Byte(), _
    offset As Integer, _
    count As Integer _
) As Task(Of Integer)
public Task<int> ReadAsync(
    byte[] buffer,
    int offset,
    int count


  • buffer
    Type: array<System..::.Byte>[]()[]
    The buffer to write the data into.
  • offset
    Type: System..::.Int32
    The byte offset in buffer at which to begin writing data from the stream.

Return Value

Type: System.Threading.Tasks..::.Task<(Of <(Int32>)>)
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.


Exception Condition

buffer is nullNothingnullptra null reference (Nothing in Visual Basic).


offset or count is negative.


The sum of offset and count is larger than the buffer length.


The stream does not support reading.


The stream has been disposed.


The stream is currently in use by a previous read operation.


The ReadAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows 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 CanRead property to determine whether the current instance supports reading.

Version Information

Windows Phone OS

Supported in: 8.1, 8.0

See Also


Stream Class

ReadAsync Overload

System.IO Namespace