WindowsRuntimeStorageExtensions.OpenStreamForReadAsync Method
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Overloads
| OpenStreamForReadAsync(IStorageFile) |
Retrieves a stream for reading from a specified file. |
| OpenStreamForReadAsync(IStorageFolder, String) |
Retrieves a stream for reading from a file in the specified parent folder. |
OpenStreamForReadAsync(IStorageFile)
Important
This API is not CLS-compliant.
Retrieves a stream for reading from a specified file.
public:
[System::Runtime::CompilerServices::Extension]
static System::Threading::Tasks::Task<System::IO::Stream ^> ^ OpenStreamForReadAsync(Windows::Storage::IStorageFile ^ windowsRuntimeFile);[System.CLSCompliant(false)]
public static System.Threading.Tasks.Task<System.IO.Stream> OpenStreamForReadAsync (this Windows.Storage.IStorageFile windowsRuntimeFile);[<System.CLSCompliant(false)>]
static member OpenStreamForReadAsync : Windows.Storage.IStorageFile -> System.Threading.Tasks.Task<System.IO.Stream><Extension()>
Public Function OpenStreamForReadAsync (windowsRuntimeFile As IStorageFile) As Task(Of Stream)Parameters
- windowsRuntimeFile
- IStorageFile
The Windows Runtime IStorageFile object to read from.
Returns
A task that represents the asynchronous read operation.
- Attributes
Exceptions
windowsRuntimeFile is null.
The file could not be opened or retrieved as a stream.
Examples
The following example shows how to open a file 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 System.Text;
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();
}
private async void Button_Click_1(object sender, RoutedEventArgs e)
{
StringBuilder contents = new StringBuilder();
string nextLine;
int lineCounter = 1;
var openPicker = new FileOpenPicker();
openPicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
openPicker.FileTypeFilter.Add(".txt");
StorageFile selectedFile = await openPicker.PickSingleFileAsync();
using (StreamReader reader = new StreamReader(await selectedFile.OpenStreamForReadAsync()))
{
while ((nextLine = await reader.ReadLineAsync()) != null)
{
contents.AppendFormat("{0}. ", lineCounter);
contents.Append(nextLine);
contents.AppendLine();
lineCounter++;
if (lineCounter > 3)
{
contents.AppendLine("Only first 3 lines shown.");
break;
}
}
}
DisplayContentsBlock.Text = contents.ToString();
}
}
}
Imports System.Text
Imports System.IO
Imports Windows.Storage.Pickers
Imports Windows.Storage
NotInheritable Public Class BlankPage
Inherits Page
Private Async Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
Dim contents As StringBuilder = New StringBuilder()
Dim nextLine As String
Dim lineCounter As Integer = 1
Dim openPicker = New FileOpenPicker()
openPicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary
openPicker.FileTypeFilter.Add(".txt")
Dim selectedFile As StorageFile = Await openPicker.PickSingleFileAsync()
Using reader As StreamReader = New StreamReader(Await selectedFile.OpenStreamForReadAsync())
nextLine = Await reader.ReadLineAsync()
While (nextLine <> Nothing)
contents.AppendFormat("{0}. ", lineCounter)
contents.Append(nextLine)
contents.AppendLine()
lineCounter = lineCounter + 1
If (lineCounter > 3) Then
contents.AppendLine("Only first 3 lines shown.")
Exit While
End If
nextLine = Await reader.ReadLineAsync()
End While
End Using
DisplayContentsBlock.Text = contents.ToString()
End Sub
End Class
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="Display lines from a file."></TextBlock>
<Button Content="Load File" Click="Button_Click_1"></Button>
<TextBlock Name="DisplayContentsBlock"></TextBlock>
</StackPanel>
</Page>
Remarks
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).
Applies to
OpenStreamForReadAsync(IStorageFolder, String)
Important
This API is not CLS-compliant.
Retrieves a stream for reading from a file in the specified parent folder.
public:
[System::Runtime::CompilerServices::Extension]
static System::Threading::Tasks::Task<System::IO::Stream ^> ^ OpenStreamForReadAsync(Windows::Storage::IStorageFolder ^ rootDirectory, System::String ^ relativePath);[System.CLSCompliant(false)]
public static System.Threading.Tasks.Task<System.IO.Stream> OpenStreamForReadAsync (this Windows.Storage.IStorageFolder rootDirectory, string relativePath);[<System.CLSCompliant(false)>]
static member OpenStreamForReadAsync : Windows.Storage.IStorageFolder * string -> System.Threading.Tasks.Task<System.IO.Stream><Extension()>
Public Function OpenStreamForReadAsync (rootDirectory As IStorageFolder, relativePath As String) As Task(Of Stream)Parameters
- rootDirectory
- IStorageFolder
The Windows Runtime IStorageFile object that contains the file to read from.
- relativePath
- String
The path, relative to the root folder, to the file to read from.
Returns
A task that represents the asynchronous read operation.
- Attributes
Exceptions
rootDirectory or relativePath is null.
relativePath is empty or contains only white-space characters.
The file could not be opened or retrieved as a stream.
Examples
The following example shows how to open a file 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;
}
}
}
}
Imports System.IO
Imports Windows.Storage
NotInheritable Public Class BlankPage
Inherits Page
Protected Overrides Sub OnNavigatedTo(e As Navigation.NavigationEventArgs)
CreateTestFile()
End Sub
Private Async Sub CreateTestFile()
Dim newFile As StorageFile = Await ApplicationData.Current.LocalFolder.CreateFileAsync("testfile.txt")
Await FileIO.WriteTextAsync(newFile, "example content in file")
End Sub
Private Async Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
Using reader As StreamReader = New StreamReader(
Await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync("testfile.txt"))
Dim contents As String = Await reader.ReadToEndAsync()
DisplayContentsBlock.Text = contents
End Using
End Sub
End Class
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>
Remarks
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).
