如何使用可变定义构建尝试/捕获

Question

在c＃中写作，我在这里得到jsonreaderexceptions：

var container = JsonConvert.DeserializeObject<HistoryResponseContainer> (responseData);

总是像未终止的线或未识别的字符一样。

我知道我需要捕获并丢弃这些错误，但是如果我尝试在try/catch语句中定义"容器"，那会破裂。这是整个方法。

foreach (String StationID in StationIDList) { 
            string url = @"http://api.wunderground.com/api/" + wundergroundkey + "/history_" + Date + "/q/pws:" + StationID + ".json";
            Uri uri = new Uri (url);
            WebRequest webRequest = WebRequest.Create (uri);
            WebResponse response = webRequest.GetResponse ();
            StreamReader streamReader = new StreamReader (response.GetResponseStream ());
            String responseData = streamReader.ReadToEnd ();
            var container = JsonConvert.DeserializeObject<HistoryResponseContainer> (responseData);
            foreach (var observation in container.history.observations) {
                CurrentData.Write (StationID + " ");
                // This makes easier access to the date. not perfect, but better.
                DateTime date = observation.date.Value;
                DateTime utc = observation.utcdate.Value;
                // whatever you want to do with each observation
                if (date.Minute == 0 || date.Minute % 5 == 0) {
                    CurrentData.Write (date.Hour + ":" + date.Minute + " " + observation.wdird + " " + observation.wspdi);
                }//end if
                CurrentData.Write ("n");
            } //End foreach observation
        } //end foreach station

Answer 1

将您的第二个foreach循环放入"尝试"（因为您使用的"容器"）。否则，如果提出异常，则不会定义它，而您仅"尝试/捕获"您的容器Intanciation：

foreach (String StationID in StationIDList) 
{ 
    string url = @"http://api.wunderground.com/api/" + wundergroundkey + "/history_" + Date + "/q/pws:" + StationID + ".json";
    Uri uri = new Uri (url);
    WebRequest webRequest = WebRequest.Create (uri);
    WebResponse response = webRequest.GetResponse ();
    StreamReader streamReader = new StreamReader (response.GetResponseStream ());
    String responseData = streamReader.ReadToEnd ();
    try
    {
        var container = JsonConvert.DeserializeObject<HistoryResponseContainer> (responseData);
        foreach (var observation in container.history.observations) 
        {
            CurrentData.Write (StationID + " ");
            DateTime date = observation.date.Value;
            DateTime utc = observation.utcdate.Value;
            if (date.Minute == 0 || date.Minute % 5 == 0) 
            {
                CurrentData.Write (date.Hour + ":" + date.Minute + " " + observation.wdird + " " + observation.wspdi);
            }
            CurrentData.Write ("n");
        }
    }
    catch(JsonReaderException ex)
    {
        // ...
    }
}

Answer 2

我知道我需要捕获并扔这些错误，

不，您需要捕获并处理这些错误。

，但是如果我尝试在尝试/捕获语句中定义"容器"，那就呕吐。

您在这里是什么意思？您需要这个：

try
{
   // your code that throws exception
}
catch(JsonReaderException ex)
{
   // handle your exception
}