WindowsRuntimeStorageExtensions.OpenStreamForReadAsync 方法

参考

定义

命名空间:: System.IO

程序集:: System.Runtime.WindowsRuntime.dll

重要

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重载

OpenStreamForReadAsync(IStorageFile)	检索流以从指定的文件中读取。
OpenStreamForReadAsync(IStorageFolder, String)	检索流以从指定的父文件夹的一个文件中读取。

OpenStreamForReadAsync(IStorageFile)

重要

此 API 不符合 CLS。

检索流以从指定的文件中读取。

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)

参数

windowsRuntimeFile: IStorageFile

要读取的 Windows 运行时 IStorageFile 对象。

Task<Stream>

表示异步读取操作的任务。

属性: CLSCompliantAttribute

例外

ArgumentNullException

windowsRuntimeFile 为 null。

IOException

无法以流的形式打开或检索文件。

示例

以下示例演示如何在 Windows 应用商店应用中以打开文件， Stream 并使用类的 StreamReader 实例读取其内容。

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

下一个示例演示与上一个示例关联的 XAML 代码。

<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>

注解

注意

在 Visual Basic 和 C# 中，可以在类型 IStorageFile为的任何对象上调用此方法作为实例方法。当使用实例方法语法调用此方法时，请省略第一个参数。有关详细信息，请参阅扩展方法 (Visual Basic) 或扩展方法 (C# 编程指南) 。

适用于

OpenStreamForReadAsync(IStorageFolder, String)

重要

此 API 不符合 CLS。

检索流以从指定的父文件夹的一个文件中读取。

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)

参数

rootDirectory: IStorageFolder

包含要读取文件的 Windows 运行时 IStorageFile 对象。

relativePath: String

相对于根文件夹，到要读取的文件的路径。

Task<Stream>

表示异步读取操作的任务。

属性: CLSCompliantAttribute

例外

ArgumentNullException

rootDirectory 或 relativePath 为 null。

ArgumentException

relativePath 为空，或者只包含空白字符。