Stream.ReadAsync Method (Byte, Int32, Int32, CancellationToken)
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.
Assemblies: mscorlib (in mscorlib.dll)
System.IO (in System.IO.dll)
[ComVisibleAttribute(false)] [HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)] public virtual Task<int> ReadAsync( byte buffer, int offset, int count, CancellationToken cancellationToken )
- Type: System.Byte
The buffer to write the data into.
- Type: System.Int32
The byte offset in buffer at which to begin writing data from the stream.
- Type: System.Int32
The maximum number of bytes to read.
Return ValueType: System.Threading.Tasks.Task<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.
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 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 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.
For an example, see the ReadAsync(Byte, Int32, Int32) overload.
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.