ReadBlockAsync Method

TextReader.ReadBlockAsync Method (Char[], Int32, Int32)

.NET Framework 4.6 and 4.5

Reads a specified maximum number of characters from the current text reader asynchronously and writes the data to a buffer, beginning at the specified index.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public virtual Task<int> ReadBlockAsync(
	char[] buffer,
	int index,
	int count


Type: System.Char[]

When this method returns, contains the specified character array with the values between index and (index + count - 1) replaced by the characters read from the current source.

Type: System.Int32

The position in buffer at which to begin writing.

Type: System.Int32

The maximum number of characters to read. If the end of the text is reached before the specified number of characters is read into the buffer, the current method returns.

Return Value

Type: 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 text has been reached.

Exception Condition

buffer is null.


index or count is negative.


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


The text reader has been disposed.


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

The task does not complete until either the number of characters specified by the count parameter are read, or the end of the text has been reached.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 4.5
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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