HTTPClient在计量连接上失败，在wifi上运行良好。

Question

我的应用程序在WiFi上运行良好，但当它通过3G连接时，它就崩溃了。

以下是代码：

protected override async void OnNavigatedTo(NavigationEventArgs e)
{
    if (!App.ViewModel.IsDataLoaded)
    {
        await App.ViewModel.LoadDataAsync();
        DataContext = App.ViewModel;
    }
}

LoadDataAsync代码

    public async Task<bool> LoadDataAsync()
    {
        Uri uri = new Uri("http://www.28cinema.az/eng/");
        HttpClient client = new HttpClient();
        HtmlDocument htmlDocument = new HtmlDocument();
        HtmlNode htmlNode = new HtmlNode(0, htmlDocument, 1);
        MovieGroup data = new MovieGroup();
        string HtmlResult;    
        HtmlResult = await client.GetStringAsync(uri);
        data.Title = "Today";
        htmlDocument.LoadHtml(HtmlResult);            
        htmlNode = htmlDocument.DocumentNode.SelectSingleNode("//div[@class='poster_wrapper']");

        for (var i = 0; i < (htmlNode.ChildNodes.Count); i++)
        {
            data.Items.Add(new MovieData
            {
                DetailsUrl = htmlNode.SelectSingleNode("div[" + (i + 1) + "]/div[1]/div[1]/a[1]").GetAttributeValue("href", ""),
                Title = htmlNode.SelectSingleNode("div[" + (i + 1) + "]/div[1]/div[1]/a[1]").InnerText,
                Poster = htmlNode.SelectSingleNode("div[" + (i + 1) + "]/img").GetAttributeValue("src", "No poster"),
                Cinema = "28 Cinema"
            });
        }
        Today = data;        
        IsDataLoaded = true;
        return true;
    }

异常消息:没有网络连接，任务被取消。

堆栈跟踪：

   at Cineman.ViewModels.MovieModel.<CreateTodayGroupAsync>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at  System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Cineman.ViewModels.MovieModel.<LoadDataAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Cineman.MainPage.<OnNavigatedTo>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>b__0(Object state)

如有任何建议，将不胜感激。

UPD:进一步查看显示了断点期间局部变量中的一行：'htmlNode.InnerHtml‘抛出了'System.NullReferenceException’类型的异常。

Answer 1

当我重新启动Visual时，它就解决了。奇怪！

Answer 2

正如您所发现的，如果您试图在没有网络连接的情况下执行HTTP请求，它将引发异常。

我建议您处理异常，例如，使用try/catch。如何向用户显示异常详细信息取决于您。