从App.OnStartup调用异步Web API方法

Question

我将App.OnStartup更改为异步，以便我可以在web api上调用异步方法，但现在我的应用程序没有显示其窗口。我在这做错了什么：

    protected override async void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        HttpResponseMessage response = await TestWebAPI();
        if (!response.IsSuccessStatusCode)
        {
            MessageBox.Show("The service is currently unavailable"); 
            Shutdown(1);
        }

        this.StartupUri = new Uri("MainWindow.xaml", UriKind.Relative);
    }

    private async Task<HttpResponseMessage> TestWebAPI()
    {
        using (var webClient = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true }))
        {
            webClient.BaseAddress = new Uri(ConfigurationManager.AppSettings["WebApiAddress"]);
            HttpResponseMessage response = await webClient.GetAsync("api/hello", HttpCompletionOption.ResponseContentRead).ConfigureAwait(false);
            return response;
        }
    }
}

如果我取消对TestWebAPI的异步调用，则显示正常。

Answer 1

我怀疑WPF希望在 StartupUri返回之前将OnStartup设置为。所以，我会尝试在Startup事件中明确创建窗口：

private async void Application_Startup(object sender, StartupEventArgs e)
{
  HttpResponseMessage response = await TestWebAPIAsync();
  if (!response.IsSuccessStatusCode)
  {
    MessageBox.Show("The service is currently unavailable"); 
    Shutdown(1);
  }
  MainWindow main = new MainWindow();
  main.DataContext = ...
  main.Show();
}

Answer 2

你试过吗？

this.OnStartup += async (s, e) =>
   {
     ...
   };

或

this.Loaded += async (s, e) =>
   {
     ...
   };

或者你可以选择另一个相关的事件。