NULL指针异常 - Android Studio

Question

我继续获得空指针异常错误。我浏览了我的代码，我不确定为什么会遇到此错误。当我补充程序

时，我会填充

错误读取NULL指针异常：尝试在null对象引用上调用虚拟方法int Java.lang.string.length（）。预先感谢。

 EditText enterCity;
TextView weatherView;

public void onClick (View view) {

    downloadAPIInfo task = new downloadAPIInfo();
    String APIKEY = "b4fabae83c89c469d7a458a230b7a267";
    String website = "http://api.openweathermap.org/data/2.5/weather?q=";
    String url = website + enterCity.getText().toString() + APIKEY;
    task.execute(url);
    Log.i("User Entry", enterCity.getText().toString());

}
public class downloadAPIInfo extends AsyncTask<String, Void, String> {
    URL url;
    HttpURLConnection httpURLConnection = null;
    String result = "";
    @Override
    protected String doInBackground(String... urls) {
        try {
            url = new URL(urls[0]);
            httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream input = httpURLConnection.getInputStream();
            InputStreamReader reader = new InputStreamReader(input);
            int data = reader.read();
            while(data != -1) {
                char one = (char) data;
                result += one;
                data = reader.read();
            }
            return result;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    //Onpostexecute interacts with the UI
    @Override
    protected void onPostExecute(String result)  {
        super.onPostExecute(result);
        try {
            String message = "";
            JSONObject object = new JSONObject(result);
            String weatherInfo = object.getString("weather");
            Log.i("Weather content", weatherInfo);

            JSONArray array = new JSONArray(weatherInfo);
            for(int i = 0; i < array.length(); i++ ) {
                JSONObject jsonPart = array.getJSONObject(i);
                Log.i("main", jsonPart.getString("main"));
                String main = "";
                String description = "";
                main = jsonPart.getString("main");
                description = jsonPart.getString("description");
                if(main != "" && description != "") {
                    message+= main + ":" + description + "rn";
                }
            }

            if(message != "") {
                weatherView.setText(message);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

        //Log.i("WebsiteContent", result);
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    enterCity = (EditText) findViewById(R.id.cityeditText);
    weatherView = (TextView) findViewById(R.id.weathertextView);

}

}

Answer 1

名为'array'的jsonArray在您的onpostexecute mehtod中为null。您的WeatherInfo字符串很可能为空。

我建议您发布完整的stacktrace，以提供更好的解释。