Windows apps
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WindowsRuntimeStreamExtensions.AsStreamForWrite Method (IOutputStream)

.NET Framework (current version)

Converts an output stream in the Windows Runtime to a managed stream in the .NET for Windows 8.x Store apps.

This API is not CLS-compliant. 

Namespace:  System.IO
Assembly:  System.Runtime.WindowsRuntime (in System.Runtime.WindowsRuntime.dll)

public static Stream AsStreamForWrite(
	this IOutputStream windowsRuntimeStream


Type: IOutputStream

The Windows Runtime IOutputStream object to convert.

Return Value

Type: System.IO.Stream
The converted stream.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IOutputStream. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


windowsRuntimeStream is null.

A default buffer size of 16,384 bytes is used when converting the stream. To specify a different buffer size, use the AsStreamForWrite(IOutputStream) overload.

The following example shows how to use the AsStreamForWrite and AsStreamForRead methods to convert a managed stream to and from a stream in the Windows Runtime.

using System;
using System.IO;
using Windows.Storage;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace ExampleApplication
    public sealed partial class BlankPage : Page
        public BlankPage()

        private async void CreateButton_Click(object sender, RoutedEventArgs e)
            StorageFile newFile = await ApplicationData.Current.LocalFolder.CreateFileAsync("testfile.txt");
            var streamNewFile = await newFile.OpenAsync(FileAccessMode.ReadWrite);

            using (var outputNewFile = streamNewFile.GetOutputStreamAt(0))
                using (StreamWriter writer = new StreamWriter(outputNewFile.AsStreamForWrite()))
                    await writer.WriteLineAsync("content for new file");
                    await writer.WriteLineAsync(UserText.Text);

        private async void VerifyButton_Click(object sender, RoutedEventArgs e)
            StorageFile openedFile = await ApplicationData.Current.LocalFolder.GetFileAsync("testfile.txt");
            var streamOpenedFile = await openedFile.OpenAsync(FileAccessMode.Read);

            using (var inputOpenedFile = streamOpenedFile.GetInputStreamAt(0))
                using (StreamReader reader = new StreamReader(inputOpenedFile.AsStreamForRead()))
                    Results.Text = await reader.ReadToEndAsync();

Here's the XAML code that is associated with the previous example.


    <StackPanel Background="{StaticResource ApplicationPageBackgroundBrush}" VerticalAlignment="Center" HorizontalAlignment="Center">
        <TextBlock Text="Provide text to write to file:"></TextBlock>
        <TextBox Name="UserText" Width="400"></TextBox>
        <Button Name="CreateButton" Content="Create File" Click="CreateButton_Click"></Button>
        <Button Name="VerifyButton" Content="Verify Contents" Click="VerifyButton_Click"></Button>
        <TextBlock Name="Results"></TextBlock>

.NET Framework

Supported in: 4.6, 4.5

.NET for Windows Phone apps

Supported in: Windows Phone Silverlight 8
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