有没有一种方法可以在创建时启动异步任务但不能在创建时启动异步任务 Xamarin

Question

我希望应用程序执行异步任务，但要先显示内容，然后启动异步任务。当我使用protected async override void OnCreate(Bundle bundle) 时，在执行异步任务之前，我看不到按钮等内容或屏幕上的内容。这完全使得使用异步任务毫无用处。

我可以通过Button.Click 实现它。但话又说回来，这不是我想要的。我想在OnCreate 设置所有视图后立即启动异步任务。也许问题出在protected async override void OnCreate(Bundle bundle)。

还有其他方法可以启动任务onCreate吗？

这是我的代码。

[Activity(Label = "NewsDetails")]
public class NewsDetails : Activity {
  protected async override void OnCreate(Bundle savedInstanceState) {
    base.OnCreate(savedInstanceState);
    SetContentView(Resource.Layout.NewsDetails);
    TextView Title = FindViewById<TextView>(Resource.Id.textTitle);
    TextView Source = FindViewById<TextView>(Resource.Id.textSource);
    WebView webDisplay = FindViewById<WebView>(Resource.Id.webDisplay);
    string thisid=Intent.GetStringExtra ("id");
    string url = "http://MyApiUrl/";
    url = url + thisid;
    var result = await GetNewsAsync(url);
    Title.Text = result.GetString("Title");
    Source.Text = result.GetString("Source");
    string ExternalReference = result.GetString("ExternalReference");
    webDisplay.Settings.JavaScriptEnabled = true;
    webDisplay.LoadUrl(ExternalReference);
  }
  private async Task<JSONObject> GetNewsAsync(string url) {
    // Create an HTTP web request using the URL:
    // Send the request to the server and wait for the response:
    // Return some JSONObject after async task here
    // Create an HTTP web request using the URL:
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
    request.ContentType = "application/json";
    request.Method = "GET";
    // Send the request to the server and wait for the response:
    using (WebResponse response = await request.GetResponseAsync()) {
      // Get a stream representation of the HTTP web response:
      using (Stream stream = response.GetResponseStream()) {
        // Use this stream to build a JSON document object:
        JSONObject jsonResponse;
        Stream jsonDoc = stream;
        Console.Out.WriteLine("Response: {0}", jsonDoc.ToString());
        StreamReader reader = new StreamReader(stream, Encoding.UTF8);
        String responseString = reader.ReadToEnd();
        jsonResponse = new JSONObject(responseString);
        JSONObject jResult = jsonResponse.GetJSONObject("Result");
        return jResult;
      }
    }
  }
}

我想知道我是否做错了什么，或者是否有完全不同的方法来实现我想要做的事情。

欢迎对代码提出任何建议。

编辑：async Task<JSONObject> GetNewsAsync 的代码。

Answer 1

我不建议将 OnCreate 方法标记为异步。

试试这样的：

protected override void OnCreate(Bundle savedInstanceState)
{
    base.OnCreate(savedInstanceState);

    SetContentView(Resource.Layout.NewsDetails);

    TextView Title = FindViewById<TextView>(Resource.Id.textTitle);
    TextView Source = FindViewById<TextView>(Resource.Id.textSource);
    WebView webDisplay = FindViewById<WebView>(Resource.Id.webDisplay);
    webDisplay.Settings.JavaScriptEnabled = true;

    string thisid=Intent.GetStringExtra ("id");
    string url = "http://MyApiUrl/";
    url = url + thisid;

    GetNewsAsync(url).ContinueWith(t=>
    {
        var result = t.Result;

        Title.Text = result.GetString("Title");
        Source.Text = result.GetString("Source");
        string ExternalReference = result.GetString("ExternalReference");

        webDisplay.LoadUrl(ExternalReference);
    });
  }