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DeflateStream::BeginRead Method

Begins an asynchronous read operation. (Consider using the ReadAsync method instead; see the Remarks section.)

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

[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
virtual IAsyncResult^ BeginRead(
	array<unsigned char>^ array, 
	int offset, 
	int count, 
	AsyncCallback^ asyncCallback, 
	Object^ asyncState
) override


Type: array<System::Byte>

The byte array to read the data into.

Type: System::Int32

The byte offset in array at which to begin reading data from the stream.

Type: System::Int32

The maximum number of bytes to read.

Type: System::AsyncCallback

An optional asynchronous callback, to be called when the read operation is complete.

Type: System::Object

A user-provided object that distinguishes this particular asynchronous read request from other requests.

Return Value

Type: System::IAsyncResult
An object that represents the asynchronous read operation, which could still be pending.


The method tried to read asynchronously past the end of the stream, or a disk error occurred.


One or more of the arguments is invalid.


Methods were called after the stream was closed.


The current DeflateStream implementation does not support the read operation.


This call cannot be completed.

Starting with the .NET Framework 4.5, you can perform asynchronous read operations by using the ReadAsync method. The BeginRead method is still available in the .NET Framework 4.5 to support legacy code; however, you can implement asynchronous I/O operations more easily by using the new async methods. For more information, see Asynchronous File I/O.

Pass the IAsyncResult return value to the EndRead method of the stream to determine how many bytes were read and to release operating system resources used for reading. You can do this either by using the same code that called BeginRead or in a callback passed to BeginRead.

The current position in the stream is updated when the asynchronous read or write operation is issued, not when the I/O operation completes.

Multiple simultaneous asynchronous requests render the request completion order uncertain.

Use the CanRead property to determine whether the current DeflateStream object supports reading.

If a stream is closed or you pass an invalid argument, exceptions are thrown immediately from BeginRead. Errors that occur during an asynchronous read request, such as a disk failure during the I/O request, occur on the thread pool thread and throw exceptions when calling EndRead.


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.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library
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