从 App.OnStartup 调用异步 Web API 方法

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不显示其窗口。我在这里做错了什么：

    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;
        }
    }
}

如果我取出对 TestWebAPI 的异步调用，它会显示正常。

我怀疑 WPF 期望StartupUri要设置before OnStartup返回。所以，我会尝试在中显式创建窗口Startup event:

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();
}