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WindowsRuntimeStorageExtensions.OpenStreamForWriteAsync Method (IStorageFile)

.NET Framework 4.5

Retrieves a stream for writing to a specified file.

This API is not CLS-compliant. 

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

[CLSCompliantAttribute(false)]
public static Task<Stream> OpenStreamForWriteAsync(
	this IStorageFile windowsRuntimeFile
)

Parameters

windowsRuntimeFile
Type: IStorageFile

The Windows Runtime IStorageFile object to write to.

Return Value

Type: System.Threading.Tasks.Task<Stream>
A task that represents the asynchronous write operation.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IStorageFile. 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).

ExceptionCondition
ArgumentNullException

windowsRuntimeFile is null.

IOException

The file could not be opened or retrieved as a stream.

The following example shows how to open a file in the application data as a Stream in a Windows Store app, and write to it by using an instance of the StreamWriter class.

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()
        {
            this.InitializeComponent();
        }

        private async void CreateButton_Click(object sender, RoutedEventArgs e)
        {
            StorageFile newFile = await ApplicationData.Current.LocalFolder.CreateFileAsync("testfile3.txt");

            using (StreamWriter writer = new StreamWriter(await newFile.OpenStreamForWriteAsync()))
            {
                await writer.WriteLineAsync("new entry");
                await writer.WriteLineAsync(UserText.Text);
            }
        }

        private async void VerifyButton_Click(object sender, RoutedEventArgs e)
        {
            StorageFile openedFile = await ApplicationData.Current.LocalFolder.GetFileAsync("testfile3.txt");
            using (StreamReader reader = new StreamReader(await openedFile.OpenStreamForReadAsync()))
            {
                Results.Text = await reader.ReadToEndAsync();
            }
        }
    }
}

The next example shows the XAML code that is associated with the previous example.

<Page
    x:Class="ExampleApplication.BlankPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:ExampleApplication"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <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>
    </StackPanel>
</Page>

.NET Framework

Supported in: 4.6, 4.5

Supported in: Windows Phone Silverlight 8
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