HttpClient.GetAsync永远不会在Xamarin.Android上返回 [英] HttpClient.GetAsync never returns on Xamarin.Android

问题描述

我正在开发一个Android应用程序，该应用程序由Azure上托管的ASP.NET Core应用程序备份.在使用Xamarin.Forms(仅Android)项目的功能之前，我正在使用共享的Library项目来测试Console Application项目上的基本内容.
以下代码段在登录到Web服务后运行，其中Client是HttpClient:

I am working on an Android application, backed up by an ASP.NET Core application hosted on Azure. I am using a shared Library project to test basic stuff on a Console Application project before making the functionalities for the Xamarin.Forms (Android-only) project.
The following piece of code is run after logging into the web service, where Client is a HttpClient:

public static async Task<MyClass> GetInformationAsync(string accountId)
{
    HttpResponseMessage response = await Client.GetAsync(UriData + "/" + accountId);
    response.EnsureSuccessStatusCode();
    string responseContent = await response.Content.ReadAsStringAsync();
    return JsonConvert.DeserializeObject<MyClass>(responseContent);
}

在同一台计算机/网络上，代码在控制台应用程序上的完成时间不到一秒钟，但是，它在Xamarin.Forms.Android项目中从未完成(甚至等待一分钟). 我觉得这很奇怪，因为Android客户端可以使用PostAsync成功登录Web服务.

Under the same computer/network, the code finishes in less than a second on the Console application, however, it never finishes (even waited a minute) in the Xamarin.Forms.Android project.
I find this weird since the Android client can successfully login to the web service using PostAsync.

但是，Android客户端和控制台客户端调用GetInformationAsync的方式有所不同.

There is a difference, however, on how the Android client and the Console client call GetInformationAsync.

当控制台客户端异步调用它时:

While the Console client calls it asynchronously:

 private static async void TestDataDownload()
 {
      ...
      var data = await WebApiClient.GetInformationAsync(myId);
 }

Android客户端同步调用它

The Android client calls it synchronously

 public void MainPage()
 {
      ...
      var data = WebApiClient.GetInformationAsync(myId).Result;
 }

推荐答案

似乎您遇到了某种僵局.您可能希望在实际调用GetInformationAsync的地方包含代码，因为这可能是问题根源所在的地方.

It seems like you are experiencing a deadlock of some sort. You might want to include the code where you actually call GetInformationAsync, as it is probably where the problem source is.

您可以通过以下方法解决问题:

You can probably fix your issue by:

1. 不以同步方式调用GetInformationAsync
2. 将GetInformationAsync中的异步调用后缀为ConfigureAwait(false)，以免在每个方法调用时切换上下文.

1. Not calling GetInformationAsync in a sync way
2. Postfixing your async calls in GetInformationAsync with ConfigureAwait(false) to not switch context on every method call.

所以您的GetInformationAsync方法如下:

public static async Task<MyClass> GetInformationAsync(string accountId)
{
    var response = await Client.GetAsync(UriData + "/" + accountId).ConfigureAwait(false);
    response.EnsureSuccessStatusCode();
    var responseContent = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
    return JsonConvert.DeserializeObject<MyClass>(responseContent);
}

然后，如果您在某个地方调用它，则需要它以返回相同的上下文，即如果您需要更新UI:

Then if you call it somewhere you need it to return back on the same context, I.e. if you need to update UI:

var myClass = await GetInformationAsync(accountId);
// update UI here...

否则，如果您不需要需要在相同的上下文中返回:

Otherwise if you don't need to return on the same context:

var myClass = await GetInformationAsync(accountId).ConfigureAwait(false);

这篇关于HttpClient.GetAsync永远不会在Xamarin.Android上返回的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！