异步下载过程中受阻于C＃WPF应用程序UI线程 [英] UI Thread blocked in C# WPF App during Async Download

问题描述

我有以下的基本WPF应用程序，在这里我想在文本框中显示的内容。然而，当我点击按钮，UI线程似乎被阻止。我不知道我在做什么错了，因为我抓住从Pluralsight课程的锻炼; Tibial这个文件code。

在XAML和code：

 ＆LT;窗​​口x：类=AsyncFetch.MainWindow
        的xmlns =htt​​p://schemas.microsoft.com/winfx/2006/xaml/$p$psentation
        的xmlns：X =htt​​p://schemas.microsoft.com/winfx/2006/xaml
        标题=主窗口HEIGHT =350WIDTH =525＆GT;
    ＆LT;网格和GT;
        ＆LT; Grid.RowDefinitions＆GT;
            ＆LT; RowDefinition高度=自动/＆GT;
            ＆LT; RowDefinition高度=*/＆GT;
        ＆LT; /Grid.RowDefinitions>        ＆LT;按钮
            X：NAME =getButton
            的Horizo​​ntalAlignment =左
            WIDTH =75
            内容=_获取数据
            点击=getButton_Click
            /＆GT;        ＆LT;文本框
            X：NAME =dataTextBox
            保证金=4
            Grid.Row =1
            /＆GT;    ＆LT; /网格和GT;
＆LT; /窗GT;
 

在code：

 命名空间AsyncFetch
{
    ///＆LT;总结＆gt;
    ///为MainWindow.xaml交互逻辑
    ///＆LT; /总结＆gt;
    公共部分类主窗口：窗口
    {
        公共主窗口（）
        {
            的InitializeComponent（）;
        }        私人异步无效getButton_Click（对象发件人，RoutedEventArgs E）
        {
            WebClient的W =新的WebClient（）;            字符串的txt =等待w.DownloadStringTaskAsync（http://www.google.com）;
            dataTextBox.Text = TXT;
        }
    }
}
 

解决方案

这不应该阻止用户界面线程，该技术是正确的。

然而，仅仅因为一个方法是异步，并返回一个任务＆LT; T＆GT; ，并不能保证的全部的方法（或它的任何）将异步运行。

在 Web客户端的情况下，控制不会返回给调用者直到请求已经完全后，prepared并启动。随着 Web客户端，我相信URI preparation，包括所有的DNS查找，可以同步发生，异步部分（实际的请求）开始，前需要哪些可以请求返回之前引起的延迟。

I have the following basic WPF app, where I want the content displayed in the text box. However, when I click on the button, the UI thread seems to be blocking. I am not sure what I am doing wrong, as I grabbed this code from the Excercise files of a Pluralsight course.

The XAML and the code:

<Window x:Class="AsyncFetch.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Button
            x:Name="getButton"
            HorizontalAlignment="Left"
            Width="75"
            Content="_Get Data"
            Click="getButton_Click"
            />

        <TextBox
            x:Name="dataTextBox"
            Margin="4"
            Grid.Row="1"
            />

    </Grid>
</Window>

The code:

namespace AsyncFetch
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void getButton_Click(object sender, RoutedEventArgs e)
        {
            WebClient w = new WebClient();

            string txt = await w.DownloadStringTaskAsync("http://www.google.com");
            dataTextBox.Text = txt;
        }
    }
}

解决方案

This shouldn't block the UI thread, and the technique is correct.

However, just because a method is Async, and returns a Task<T>, doesn't guarantee that the entire method (or any of it) will run asynchronously.

In the case of WebClient, the control won't return to the caller until after the request has been completely prepared and started. With WebClient, I believe the URI preparation, including all of the DNS lookups, can happen synchronously and is required before the asynchronous portion (the actual request) begins, which can cause a delay before the request returns.

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