Android Studio-创建类以在所有活动中读取Json本地文件

Question

I am trying to create a class that I can call on each activities in my app in order to read a local JSON file.

The function I have works fine if inside MainActivity.java however, when I try to create I get a crash in the app. I understand I have to create a Context in my java Class but I am trying everything and I cannot get it to work.

What am I missing?

MainActivity.java

Button botton2 = (Button) findViewById(R.id.bottone2);
        final TextView text2 = (TextView) findViewById(R.id.textView2);


        botton2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String jsonValue = jsonClass.getJsonValue("file.json", "aa", "bob", "text");      

                testo.setText(jsonValue);

            }
        });

JSON Class:

public class jsonClass extends Application {

    private static Context mContext;
    private static InputStream is = null;
    //static AssetManager am = mContext.getResources().getAssets();

    @Override
    public void onCreate() {
        super.onCreate();
        mContext = this;
    }

    public static Context getContext(){
        return mContext;
    }


    public static String loadJSONFromAsset(String file)  {
        String json = null;
        try {

            is = jsonClass.getContext().getResources().getAssets().open(file);

            int size = is.available();

            byte[] buffer = new byte[size];

            is.read(buffer);

            is.close();

            json = new String(buffer, "UTF-8");


        } catch (IOException ex) {
            ex.printStackTrace();
            return null;
        }
        return json;

    }


    public static String getJsonValue(String jsonFile, String anni, String level, String getValue) {
        String value = null;

        JSONObject object = null;
        try {

            object = new JSONObject(loadJSONFromAsset(jsonFile));

            JSONObject getEra = object.getJSONObject(anni);

            JSONObject getLevel = getEra.getJSONObject(level);

            value = getLevel.getString(getValue);

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

        return value;
    }
}

Answer 1

Your Json class doesn't need to extend Application.

Instead try :

public class JsonClass {

   private static mContext;

   public JsonClass(Context context) {
       mContext = context;
    }

   ...
 }

Now instantiate it from your Main.java like this:

JsonClass json = new JsonClass(this);