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StringReader.ReadAsync Method

.NET Framework 4.5

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

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

<ComVisibleAttribute(False)> _
Public Overrides Function ReadAsync ( _
	buffer As Char(), _
	index As Integer, _
	count As Integer _
) As Task(Of Integer)


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 string is reached before the specified number of characters is written into the buffer, the method returns.

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 string has been reached.


buffer is Nothing.


index or count is negative.


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


The string reader has been disposed.


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

The task completes after either the number of characters specified by the count parameter are read or the end of the string is reached.

The following example shows how to read the first 23 characters of a string asynchronously.

Imports System.IO

Module Module1

    Sub Main()
    End Sub

    Async Sub ReadCharacters()
        Dim stringToRead = "Some characters to read but not all" 
        Dim charsRead(stringToRead.Length) As Char 

        Using reader As StringReader = New StringReader(stringToRead)
            Await reader.ReadAsync(charsRead, 0, 23)
        End Using 
    End Sub 

End Module 
' The example displays the following output: 
' Some characters to read 

.NET Framework

Supported in: 4.6, 4.5

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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