Question

我正在尝试为天气创建一个Android应用程序。在一些失败的结果之后，我决定尝试从互联网上获取代码。它仍然不起作用。我在这里找到它：https://androstock.com/tutorials/create-a-weather-app-on-android-android-studio.html 我收到的错误是：

我已经用我的实际API密钥检查了该网址-在浏览器中有效。

MainActivity：

public class MainActivity extends AppCompatActivity {
    TextView selectCity, cityField, detailsField, currentTemperatureField, humidity_field, pressure_field, weatherIcon, updatedField;
    ProgressBar loader;
    Typeface weatherFont;
    String city = "Rome, IT";
    /* Please Put your API KEY here */
    String OPEN_WEATHER_MAP_API = "f2b6e17d5a21b6580934286ac8fa696a";
    /* Please Put your API KEY here */


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        loader = (ProgressBar) findViewById(R.id.loader);
        selectCity = (TextView) findViewById(R.id.selectCity);
        cityField = (TextView) findViewById(R.id.city_field);
        updatedField = (TextView) findViewById(R.id.updated_field);
        detailsField = (TextView) findViewById(R.id.details_field);
        currentTemperatureField = (TextView) findViewById(R.id.current_temperature_field);
        humidity_field = (TextView) findViewById(R.id.humidity_field);
        pressure_field = (TextView) findViewById(R.id.pressure_field);
        weatherIcon = (TextView) findViewById(R.id.weather_icon);
        weatherFont = Typeface.createFromAsset(getAssets(), "fonts/weathericons-regular-webfont.ttf");
        weatherIcon.setTypeface(weatherFont);

        taskLoadUp(city);

        selectCity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this);
                alertDialog.setTitle("Change City");
                final EditText input = new EditText(MainActivity.this);
                input.setText(city);
                LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
                        LinearLayout.LayoutParams.MATCH_PARENT,
                        LinearLayout.LayoutParams.MATCH_PARENT);
                input.setLayoutParams(lp);
                alertDialog.setView(input);

                alertDialog.setPositiveButton("Change",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                city = input.getText().toString();
                                taskLoadUp(city);
                            }
                        });
                alertDialog.setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                dialog.cancel();
                            }
                        });
                alertDialog.show();
            }
        });

    }


    public void taskLoadUp(String query) {
        if (Function.isNetworkAvailable(getApplicationContext())) {
            Log.w("myApp", "network available in main 91");
            DownloadWeather task = new DownloadWeather();
            task.execute(query);
        } else {
            Toast.makeText(getApplicationContext(), "No Internet Connection", Toast.LENGTH_LONG).show();
        }
    }



    class DownloadWeather extends AsyncTask < String, Void, String > {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            loader.setVisibility(View.VISIBLE);

        }
        protected String doInBackground(String...args) {
            String xml = Function.excuteGet("http://api.openweathermap.org/data/2.5/weather?q=" + args[0] +
                    "&units=metric&appid=" + OPEN_WEATHER_MAP_API);
            Log.w("myApp", "xml is " +xml);
            return xml;
        }
        @Override
        protected void onPostExecute(String xml) {
            try {
                JSONObject json = new JSONObject(xml);
                if (json != null) {
                    JSONObject details = json.getJSONArray("weather").getJSONObject(0);
                    JSONObject main = json.getJSONObject("main");
                    DateFormat df = DateFormat.getDateTimeInstance();

                    cityField.setText(json.getString("name").toUpperCase(Locale.US) + ", " + json.getJSONObject("sys").getString("country"));
                    detailsField.setText(details.getString("description").toUpperCase(Locale.US));
                    currentTemperatureField.setText(String.format("%.2f", main.getDouble("temp")) + "°");
                    humidity_field.setText("Humidity: " + main.getString("humidity") + "%");
                    pressure_field.setText("Pressure: " + main.getString("pressure") + " hPa");
                    updatedField.setText(df.format(new Date(json.getLong("dt") * 1000)));
                    weatherIcon.setText(Html.fromHtml(Function.setWeatherIcon(details.getInt("id"),
                            json.getJSONObject("sys").getLong("sunrise") * 1000,
                            json.getJSONObject("sys").getLong("sunset") * 1000)));

                    loader.setVisibility(View.GONE);

                }else{
                    Toast.makeText(getApplicationContext(), "Json variable is null", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e) {
                Toast.makeText(getApplicationContext(), "Error, Check City", Toast.LENGTH_SHORT).show();
            }


        }
    }

}

功能：

public class Function {

    // Project Created by Ferdousur Rahman Shajib
    // www.androstock.com

    public static boolean isNetworkAvailable(Context context)
    {
        return ((ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo() != null;
    }



    public static String excuteGet(String targetURL)
    {
        URL url;
        HttpURLConnection connection = null;
        try {
            //Create connection
            url = new URL(targetURL);
            connection = (HttpURLConnection)url.openConnection();
            connection.setRequestProperty("content-type", "application/json;  charset=utf-8");
            connection.setRequestProperty("Content-Language", "en-US");
            connection.setUseCaches (false);
            connection.setDoInput(true);
            connection.setDoOutput(false);

            InputStream is;
            int status = connection.getResponseCode();
            if (status != HttpURLConnection.HTTP_OK)
                is = connection.getErrorStream();
            else
                is = connection.getInputStream();
            BufferedReader rd = new BufferedReader(new InputStreamReader(is));
            String line;
            StringBuffer response = new StringBuffer();
            while((line = rd.readLine()) != null) {
                response.append(line);
                response.append('\r');
            }
            rd.close();
            return response.toString();
        } catch (Exception e) {
            return null;
        } finally {
            if(connection != null) {
                connection.disconnect();
            }
        }
    }


    public static String setWeatherIcon(int actualId, long sunrise, long sunset){
        int id = actualId / 100;
        String icon = "";
        if(actualId == 800){
            long currentTime = new Date().getTime();
            if(currentTime>=sunrise && currentTime<sunset) {
                icon = "&#xf00d;";
            } else {
                icon = "&#xf02e;";
            }
        } else {
            switch(id) {
                case 2 : icon = "&#xf01e;";
                    break;
                case 3 : icon = "&#xf01c;";
                    break;
                case 7 : icon = "&#xf014;";
                    break;
                case 8 : icon = "&#xf013;";
                    break;
                case 6 : icon = "&#xf01b;";
                    break;
                case 5 : icon = "&#xf019;";
                    break;
            }
        }
        return icon;
    }


}

输出：

FATAL EXCEPTION: main
Process: com.example.weatherapp, PID: 30032
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
    at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
    at org.json.JSONTokener.nextValue(JSONTokener.java:94)
    at org.json.JSONObject.<init>(JSONObject.java:159)
    at org.json.JSONObject.<init>(JSONObject.java:176)
    at com.example.weatherapp.MainActivity$DownloadWeather.onPostExecute(MainActivity.java:117)
    at com.example.weatherapp.MainActivity$DownloadWeather.onPostExecute(MainActivity.java:101)
    at android.os.AsyncTask.finish(AsyncTask.java:695)
    at android.os.AsyncTask.access$600(AsyncTask.java:180)
    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:712)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2019-02-09 18:27:45.489 30032-30032/com.example.weatherapp I/Process: Sending signal. PID: 30032 SIG: 9

该应用程序开始启动，但立即关闭。

编辑：我认为问题不应该是重复的，因为问题不是源于对象的错误初始化，而是源于未在清单文件中添加特定行

Answer 1

问题可能出在清单中的internet权限和cleartext HTTP traffic值权限。请确保添加

?xml version="1.0" encoding="utf-8"?>

    <manifest ...>
        <uses-permission android:name="android.permission.INTERNET" />
        <application
            ...
            android:usesCleartextTraffic="true"
            ...>
            ...
        </application>
    </manifest>

为什么我从AsyncTask获得NullPointerException？

1 个答案: