Question

我想在 xamarin android 项目中运行以下委托。

但是在运行之后，State类的对象S包含null。此错误指向代码中的以下行。

tv.Text = s.name+""+s.population;

tv在我的代码中是textview。

button.Click += async delegate {

    state s = new state();
    HttpClient _client = new HttpClient();
    string url = "http://iforindia.azurewebsites.net/api/state/uid/33F8A8D5-0DF2-47A0-9C79-002351A95F88";
    HttpResponseMessage response = await _client.GetAsync(url);
    if (response.ReasonPhrase.Contains("OK"))
    {
        if (response != null)
        {
            var jsonSerializer = new DataContractJsonSerializer(typeof(state));
            var stream = await response.Content.ReadAsStreamAsync();
            s= (state)jsonSerializer.ReadObject(stream);
        }
    }
    else if (response.ReasonPhrase.Contains("Bad Request"))
    {
        s= null;
    }
    else
    {
        s= null;
    }
    tv.Text = s.name+""+s.population;
};

Answer 1

这是多余的（response.ReasonPhase已经引发了一个空异常）：

if (response != null)

试试这个：

 button.Click += async delegate {

    var client = new HttpClient();
    var url = "http://iforindia.azurewebsites.net/api/state/uid/33F8A8D5-0DF2-47A0-9C79-002351A95F88";
    var response = await _client.GetAsync(url);
    if (response != null && response.ReasonPhrase.Contains("OK"))
    {
            var jsonSerializer = new DataContractJsonSerializer(typeof(state));
            var stream = await response.Content.ReadAsStreamAsync();
            var s = jsonSerializer.ReadObject(stream) as state;

            if (s != null)
            {
                 tv.Text = s.name+""+s.population;
            }   
        }
   };

抛出了system.runtime.serialization.serializationException

1 个答案: