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WindowsRuntimeStorageExtensions.OpenStreamForReadAsync Method (IStorageFolder, String)

.NET Framework 4.5

Retrieves a stream for reading from a file in the specified parent folder.

This API is not CLS-compliant. 

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

[CLSCompliantAttribute(false)]
public static Task<Stream> OpenStreamForReadAsync(
	this IStorageFolder rootDirectory,
	string relativePath
)

Parameters

rootDirectory
Type: IStorageFolder

The Windows Runtime IStorageFolder object that contains the file to read from.

relativePath
Type: System.String

The path, relative to the root folder, to the file to read from.

Return Value

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

Usage Note

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

rootDirectory or relativePath is null.

ArgumentException

relativePath is empty or contains only white-space characters.

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 read its contents by using an instance of the StreamReader class.

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

namespace ExampleApplication
{
    public sealed partial class BlankPage : Page
    {
        public BlankPage()
        {
            this.InitializeComponent();
            CreateTestFile();
        }

        private async void CreateTestFile()
        {
            StorageFile newFile = await ApplicationData.Current.LocalFolder.CreateFileAsync("testfile.txt");
            await FileIO.WriteTextAsync(newFile, "example content in file");
        }

        private async void Button_Click_1(object sender, RoutedEventArgs e)
        {
            using (StreamReader reader = new StreamReader(
                await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync("testfile.txt")))
            {
                string contents = await reader.ReadToEndAsync();   
                DisplayContentsBlock.Text = contents;
            }
        }
    }
}

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">
        <Button Content="Open File" Click="Button_Click_1"></Button>
        <TextBlock Name="DisplayContentsBlock"></TextBlock>
    </StackPanel>
</Page>

.NET Framework

Supported in: 4.5

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone Silverlight 8

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012

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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