JSON 异常和权限答案

【问题标题】：JSON exception and permissionsJSON 异常和权限
【发布时间】：2017-02-26 01:34:36
【问题描述】：

我已经使用开放天气 API 编写了天气应用程序....但是当我在手机中安装该应用程序并单击按钮以确定天气时它崩溃了...我在手机中使用 Android M

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 msg = "";
            JSONObject jsonObject = new JSONObject(result);
            String weatherInfo = jsonObject.getString("weather");

            JSONArray arr = new JSONArray(weatherInfo);
            for(int i = 0;i<arr.length();i++){
                JSONObject jsonPart = arr.getJSONObject(i);
                String main = "";
                String desc = "";

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

                if (main != "" && desc != "") {
                    msg += main + "\r\n" + desc;
                }

            }

            if(msg != ""){
                weatherReport.setText(msg);
            }
            else{
                Toast.makeText(MainActivity.this,
                        "Location not able to determine",Toast.LENGTH_LONG).show();
            }

        } catch (JSONException e) {
            Toast.makeText(MainActivity.this,
                    "Location not able to determine",Toast.LENGTH_LONG).show();
            e.printStackTrace();
        }

    }
}

显示的错误是 arr.length() 应用于空数组.... 我不明白错误是什么。是关于权限...如果是这样我应该如何在 Marshmallow 中实现权限...这是 onCreate() 内部的代码，如果它与权限有关，请告诉如何实现..

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);

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

Logcat ..

02-25 22:56:54.009 1413-1413/com.example.hemantj.weather E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.example.hemantj.weather, PID: 1413
                                                                       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)

【问题讨论】：

在这里发布日志猫
也发布你的 JSON
替换这一行 JSONArray arr = new JSONArray(weatherInfo);使用 JSONArray arr = new weatherInfo.getJSONArray(0);或用于循环的多个数据
张贴日志猫..请现在回答..另外请注意，我使用 ANDROID TARGET SDK 作为 25 和 min SDK 作为 23..

标签： android json permissions

【解决方案1】：

 try {
                    Log.d(TAG, "onPostExecute: this inner of post" + getcontent_for_validate);
                    jsonobj = new JSONObject(getcontent_for_validate);
                    System.out.println("this is get content" + jsonobj.toString());


                    JSONArray array = jsonobj.getJSONArray("Staff_Details");
                    for (int i = 0; i < array.length(); i++) {
                        Clint_id = editText_user_name.getText().toString();
                        Api_key = array.getJSONObject(i).getString("api_key");
                       COMPANY_LOGO = array.getJSONObject(i).getString("company_logo");
                        Password = editText_password.getText().toString();
                    }


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

仅限互联网权限

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

【讨论】：

【解决方案2】：

错误在你的 onPostExecute() 中

new JSONArray(weatherInfo);  //is returning null

so arr is null

weatherInfo 的价值是什么？

【讨论】：

weatherInfo = jsonObject.getString("weather");