android - Xamarin 和 Android - 退出方法时崩溃

Question

我不知道还能说些什么。我有这个方法:

public async Task<HttpResponseMessage> SendAsyncRequest(string uri, string content, HttpMethod method, bool tryReauthorizeOn401 = true)
{
    HttpRequestMessage rm = new HttpRequestMessage(method, uri);
    if (!string.IsNullOrWhiteSpace(content))
        rm.Content = new StringContent(content, Encoding.UTF8, "application/json");

    HttpResponseMessage response = await client.SendAsync(rm);
    if (response.StatusCode == HttpStatusCode.Unauthorized && tryReauthorizeOn401)
    {
        var res = await AuthenticateUser();
        if(res.user == null)
            return response;
        return await SendAsyncRequest(uri, content, method, false);
    }

    return response;
}

没什么特别的。client.SendAsync(rm) 已执行，response.StatusCode 正常。应用程序在退出此方法时崩溃。

输出只显示了这个断言:

12-16 20:09:22.025 F/        ( 1683): * Assertion at /Users/builder/jenkins/workspace/xamarin-android-d15-9/xamarin-android/external/mono/mono/mini/debugger-agent.c:4957, condition `is_ok (error)' not met, function:set_set_notification_for_wait_completion_flag, Could not execute the method because the containing type is not fully instantiated. assembly:<unknown assembly> type:<unknown type> member:(null)
12-16 20:09:22.025 F/libc    ( 1683): Fatal signal 6 (SIGABRT), code -6 in tid 1683 (omerang.Android)

仅此而已。客户端是 HttpClient。我在我的 Android 项目中进行了设置:HttpClient Implementation 设置为 Android。

有谁知道哪里出了问题？

编辑

SendAsyncRequest 是这样使用的:

public async Task<(HttpResponseMessage response, IEnumerable<T> items)> GetListFromRequest<T>(string uri)
{
    HttpResponseMessage response = await SendAsyncRequest(uri, null, HttpMethod.Get);
    if (!response.IsSuccessStatusCode)
        return (response, null);

    string content = await response.Content.ReadAsStringAsync();
    var items = JsonConvert.DeserializeObject<IEnumerable<T>>(content);
    return (response, new List<T>(items));
}

Answer 1

基于您提供的示例项目代码

protected override async void OnStart()
{
    Controller c = new Controller();
    TodoItem item = await c.GetTodoItem(1);
    TodoItem item2 = await c.GetTodoItem(2);
}

您正在调用 async void 在启动时触发并忘记。

您将无法捕获任何抛出的异常，这可以解释为什么应用程序会在没有警告的情况下崩溃。

引用 Async/Await - Best Practices in Asynchronous Programming

async void 应该只与事件处理程序一起使用，所以我建议添加一个事件和处理程序。

根据提供的示例，它可能如下所示

public partial class App : Application {
    public App() {
        InitializeComponent();
        MainPage = new MainPage();
    }

    private even EventHander starting = delegate { };
    private async void onStarting(object sender, EventArgs args) {
        starting -= onStarting;
        try {
            var controller = new Controller();
            TodoItem item = await controller.GetTodoItem(1);
            TodoItem item2 = await controller.GetTodoItem(2);
        } catch(Exception ex) {
            //...handler error here
        }
    }

    protected override void OnStart() {
        starting += onStarting;
        starting(this, EventArgs.Empty);
    }

    //...omitted for brevity
}

这样，您现在至少应该能够捕获抛出的异常以确定失败的原因。