Stream.CopyToAsync Method

Definition

Namespace:

System.IO

Assembly:

System.Runtime.dll

Asynchronously reads the bytes from the current stream and writes them to another stream. Both streams positions are advanced by the number of bytes copied.

Overloads

CopyToAsync(Stream, Int32, CancellationToken)	Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified buffer size and cancellation token. Both streams positions are advanced by the number of bytes copied.
CopyToAsync(Stream, CancellationToken)	Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified cancellation token. Both streams positions are advanced by the number of bytes copied.
CopyToAsync(Stream)	Asynchronously reads the bytes from the current stream and writes them to another stream. Both streams positions are advanced by the number of bytes copied.
CopyToAsync(Stream, Int32)	Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified buffer size. Both streams positions are advanced by the number of bytes copied.

CopyToAsync(Stream, Int32, CancellationToken)

Source:

Stream.cs

Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified buffer size and cancellation token. Both streams positions are advanced by the number of bytes copied.

public:
 virtual System::Threading::Tasks::Task ^ CopyToAsync(System::IO::Stream ^ destination, int bufferSize, System::Threading::CancellationToken cancellationToken);

public virtual System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination, int bufferSize, System.Threading.CancellationToken cancellationToken);

abstract member CopyToAsync : System.IO.Stream * int * System.Threading.CancellationToken -> System.Threading.Tasks.Task
override this.CopyToAsync : System.IO.Stream * int * System.Threading.CancellationToken -> System.Threading.Tasks.Task

Public Overridable Function CopyToAsync (destination As Stream, bufferSize As Integer, cancellationToken As CancellationToken) As Task

Parameters

destination

Stream

The stream to which the contents of the current stream will be copied.

bufferSize

Int32

The size, in bytes, of the buffer. This value must be greater than zero. The default size is 81920.

cancellationToken

CancellationToken

The token to monitor for cancellation requests. The default value is None.

Returns

Task

A task that represents the asynchronous copy operation.

Exceptions

ArgumentNullException

destination is null.

ArgumentOutOfRangeException

buffersize is negative or zero.

ObjectDisposedException

Either the current stream or the destination stream is disposed.

NotSupportedException

The current stream does not support reading, or the destination stream does not support writing.

OperationCanceledException

The cancellation token was canceled. This exception is stored into the returned task.

Remarks

The CopyToAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows 8.x 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#.

If the operation is canceled before it completes, the returned task contains the Canceled value for the Status property.

Copying begins at the current position in the current stream.

For an example of copying between two streams, see the CopyToAsync(Stream) overload.

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by CopyTo(Stream, Int32).

CopyToAsync(Stream, CancellationToken)

Source:

Stream.cs

Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified cancellation token. Both streams positions are advanced by the number of bytes copied.

public:
 System::Threading::Tasks::Task ^ CopyToAsync(System::IO::Stream ^ destination, System::Threading::CancellationToken cancellationToken);

public System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination, System.Threading.CancellationToken cancellationToken);

member this.CopyToAsync : System.IO.Stream * System.Threading.CancellationToken -> System.Threading.Tasks.Task

Public Function CopyToAsync (destination As Stream, cancellationToken As CancellationToken) As Task

Parameters

destination

Stream

The stream to which the contents of the current stream will be copied.

cancellationToken

CancellationToken

The token to monitor for cancellation requests. The default value is None.

Returns

Task

A task that represents the asynchronous copy operation.

Exceptions

OperationCanceledException

The cancellation token was canceled. This exception is stored into the returned task.

Remarks

The CopyToAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows 8.x 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#.

If the operation is canceled before it completes, the returned task contains the Canceled value for the Status property.

Copying begins at the current position in the current stream.

For an example of copying between two streams, see the CopyToAsync(Stream) overload.

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by CopyTo(Stream).

CopyToAsync(Stream)

Source:

Stream.cs

Asynchronously reads the bytes from the current stream and writes them to another stream. Both streams positions are advanced by the number of bytes copied.

public:
 System::Threading::Tasks::Task ^ CopyToAsync(System::IO::Stream ^ destination);

public System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination);

member this.CopyToAsync : System.IO.Stream -> System.Threading.Tasks.Task

Public Function CopyToAsync (destination As Stream) As Task

Parameters

destination

Stream

The stream to which the contents of the current stream will be copied.

Returns

Task

A task that represents the asynchronous copy operation.

Exceptions

ArgumentNullException

destination is null.

ObjectDisposedException

Either the current stream or the destination stream is disposed.

NotSupportedException

The current stream does not support reading, or the destination stream does not support writing.

Examples

The following example demonstrates how to use two FileStream objects to asynchronously copy the files from one directory to another. The FileStream class derives from the Stream class. Notice that the Click event handler for the Button control is marked with the async modifier because it calls an asynchronous method

using System;
using System.Threading.Tasks;
using System.Windows;
using System.IO;

namespace WpfApplication
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            string StartDirectory = @"c:\Users\exampleuser\start";
            string EndDirectory = @"c:\Users\exampleuser\end";

            foreach (string filename in Directory.EnumerateFiles(StartDirectory))
            {
                using (FileStream SourceStream = File.Open(filename, FileMode.Open))
                {
                    using (FileStream DestinationStream = File.Create(EndDirectory + filename.Substring(filename.LastIndexOf('\\'))))
                    {
                        await SourceStream.CopyToAsync(DestinationStream);
                    }
                }
            }
        }
    }
}

Imports System.IO

Class MainWindow

    Private Async Sub Button_Click(sender As Object, e As RoutedEventArgs)
        Dim StartDirectory As String = "c:\Users\exampleuser\start"
        Dim EndDirectory As String = "c:\Users\exampleuser\end"

        For Each filename As String In Directory.EnumerateFiles(StartDirectory)
            Using SourceStream As FileStream = File.Open(filename, FileMode.Open)
                Using DestinationStream As FileStream = File.Create(EndDirectory + filename.Substring(filename.LastIndexOf("\"c)))
                    Await SourceStream.CopyToAsync(DestinationStream)
                End Using

            End Using
        Next
    End Sub

End Class

Remarks

The CopyToAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows 8.x 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#.

Copying begins at the current position in the current stream.

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by CopyTo(Stream).

CopyToAsync(Stream, Int32)

Source:

Stream.cs

Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified buffer size. Both streams positions are advanced by the number of bytes copied.

public:
 System::Threading::Tasks::Task ^ CopyToAsync(System::IO::Stream ^ destination, int bufferSize);

public System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination, int bufferSize);

member this.CopyToAsync : System.IO.Stream * int -> System.Threading.Tasks.Task

Public Function CopyToAsync (destination As Stream, bufferSize As Integer) As Task

Parameters

destination

Stream

The stream to which the contents of the current stream will be copied.

bufferSize

Int32

The size, in bytes, of the buffer. This value must be greater than zero. The default size is 81920.

Returns

Task

A task that represents the asynchronous copy operation.

Exceptions

ArgumentNullException

destination is null.

ArgumentOutOfRangeException

buffersize is negative or zero.

ObjectDisposedException

Either the current stream or the destination stream is disposed.

NotSupportedException

The current stream does not support reading, or the destination stream does not support writing.

Remarks

The CopyToAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows 8.x 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#.

Copying begins at the current position in the current stream.

For an example of copying between two streams, see the CopyToAsync(Stream) overload.

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by CopyTo(Stream, Int32).