JSON天气API错误

Question

我已经使用开放天气api创建了一个天气应用程序，当我单击按钮来确定天气时，它会崩溃。下面是logcat

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:156)
                                                                           at org.json.JSONObject.<init>(JSONObject.java:173)
                                                                           at com.example.hemantj.weather.MainActivity$DownloadTask.onPostExecute(MainActivity.java:133)
                                                                           at com.example.hemantj.weather.MainActivity$DownloadTask.onPostExecute(MainActivity.java:92)
                                                                           at android.os.AsyncTask.finish(AsyncTask.java:651)
                                                                           at android.os.AsyncTask.access$500(AsyncTask.java:180)
                                                                           at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5451)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

下面是代码..。我已经使用了ANDROID TARGET SDK 25和MIN SDK as 23。所以牵涉到了棉花糖..因此，如果与权限相关的任何事情都是错误的，也请指出...

weather.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            if(checkSelfPermission(Manifest.permission.INTERNET) == PackageManager.PERMISSION_GRANTED){

                try {

                    //to hide the keyboard after pressing the button
                    InputMethodManager manager =
                            (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
                    manager.hideSoftInputFromInputMethod(weatherInput.getWindowToken(),0);

                    DownloadTask downloadTask = new DownloadTask();

                    //used to encode the entered input for url.. for example San Fransisco appears in url
                    //as San%20Fransisco ... and to enable that we use the encoder...
                    String encodedCity = URLEncoder.encode(city,"UTF-8");

                    downloadTask.execute("http://api.openweathermap.org/data/2.5/weather?q=" + encodedCity + "&APPID=0a7808bb8061814df9b6d5fc88d58b8f");

                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }

            }
            else{
                if(shouldShowRequestPermissionRationale(Manifest.permission.INTERNET)){

                    Toast.makeText(MainActivity.this,
                            "Internet permissions are necessary",Toast.LENGTH_LONG).show();

                }

                requestPermissions(new String[]{Manifest.permission.INTERNET},INTERNET_CODE);
            }
        }
    });
}

public class DownloadTask extends AsyncTask<String, Void, String>{

    @Override
    protected String doInBackground(String... urls) {

        String result = "";
        URL url;
        HttpURLConnection httpURLConnection = null;

        try {
            url = new URL(urls[0]);
            httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream in = httpURLConnection.getInputStream();
            InputStreamReader reader = new InputStreamReader(in);
            int data = reader.read();
            while(data != -1){
                char current = (char) data;
                result += current;

                data = reader.read();
            }
            return result;

        }
        //combined the exceptions MalformedURL and IOException to a common to display a toast msg
        catch (Exception e) {
            e.printStackTrace();
        }

        return null;

    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        try {

            String message = "";

            JSONObject jsonObject = new JSONObject(result);

            String weatherInfo = jsonObject.getString("weather");

            Log.i("Weather content", weatherInfo);

            JSONArray arr = new JSONArray(weatherInfo);

            for (int i = 0; i < arr.length(); i++) {

                JSONObject jsonPart = arr.getJSONObject(i);

                String main = "";
                String description = "";

                main = jsonPart.getString("main");
                description = jsonPart.getString("description");

                if (main != "" && description != "") {

                    message += main + ": " + description + "\r\n";

                }

            }

            if (message != "") {

                weatherReport.setText(message);

            } else {

                Toast.makeText(getApplicationContext(), "Could not find weather", Toast.LENGTH_LONG).show();

            }


        } catch (JSONException e) {

            Toast.makeText(getApplicationContext(), "Could not find weather", Toast.LENGTH_LONG).show();

        }

    }
}

Answer 1

您缺少API key，因此将返回一个错误，并且String weatherInfo = jsonObject.getString("weather");为空。所以当你尝试获取数组的.length时，它是空的。创建另一个String对象，如下所示：

String apiKey = "Put API key here"；

然后改变：

此

 downloadTask.execute("http://api.openweathermap.org/data/2.5/weather?q=" + encodedCity);

指向此的

downloadTask.execute("http://api.openweathermap.org/data/2.5/weather?q=" + encodedCity + "&appid=" + apiKey);

此外，请确保您在清单中具有internet权限。

<uses-permission android:name="android.permission.INTERNET" />