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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
Assembly:  mscorlib (in mscorlib.dll)
[ComVisibleAttribute(false)]
public override Task<int> ReadAsync(
	char[] buffer,
	int index,
	int count
)

Parameters

buffer
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.

index
Type: System.Int32

The position in buffer at which to begin writing.

count
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<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.
ExceptionCondition
ArgumentNullException

buffer is null.

ArgumentOutOfRangeException

index or count is negative.

ArgumentException

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

ObjectDisposedException

The string reader has been disposed.

InvalidOperationException

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.

using System;
using System.IO;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            ReadCharacters();
        }

        static async void ReadCharacters()
        {
            string stringToRead = "Some characters to read but not all";
            char[] charsRead = new char[stringToRead.Length];

            using (StringReader reader = new StringReader(stringToRead))
            {
                await reader.ReadAsync(charsRead, 0, 23);
                Console.WriteLine(charsRead);
            }
        }
    }
}
// The example displays the following output: 
// Some characters to read 
//

.NET Framework

Supported in: 4.5.1, 4.5

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

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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