尝试调用虚拟方法 'android.content.SharedPreferences android.content.Context.getSharedPreferences [英] Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences

问题描述

我正在尝试使用 SharedPreferences 将我从 Json URL 获得的 Json 对象保存到收藏夹列表，但是每次当我尝试保存 Json Array 时应用程序崩溃并出现下一个错误:

I'm trying to save Json object which I got from Json URL to favorite list using SharedPreferences but The app crashes every time when I try to save Json Array with next error:

06-27 18:36:03.224      933-933/? E/EGL_emulation﹕ tid 933: eglCreateSyncKHR(1237): error 0x3004 (EGL_BAD_ATTRIBUTE)
06-27 18:36:27.496    2778-2778/? E/memtrack﹕ Couldn't load memtrack module (No such file or directory)
06-27 18:36:27.496    2778-2778/? E/android.os.Debug﹕ failed to load memtrack module: -2
06-27 18:36:27.943    2793-2793/? E/memtrack﹕ Couldn't load memtrack module (No such file or directory)
06-27 18:36:27.943    2793-2793/? E/android.os.Debug﹕ failed to load memtrack module: -2
06-27 18:36:53.230    2807-2807/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.boom.kayakapp, PID: 2807
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
            at com.boom.kayakapp.util.SharedPreference.getFavorites(SharedPreference.java:60)
            at com.boom.kayakapp.util.SharedPreference.addFavorite(SharedPreference.java:41)
            at com.boom.kayakapp.activities.MainActivity$2.onItemLongClick(MainActivity.java:124)
            at android.widget.AbsListView.performLongPress(AbsListView.java:3121)
            at android.widget.AbsListView$CheckForLongPress.run(AbsListView.java:3070)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-27 18:36:53.264      933-933/? E/EGL_emulation﹕ tid 933: eglCreateSyncKHR(1237): error 0x3004 (EGL_BAD_ATTRIBUTE)

我如何理解错误意味着当我尝试将 Json 对象保存到共享首选项时，方法调用空对象引用，但我无法理解代码有什么问题...

How I could understand the error means that when I try to save Json object to shared preferences, method calls null object reference, but I can't understand what's wrong with code...

这是我的主要活动:

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.os.StrictMode;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;
import com.boom.kayakapp.R;
import com.boom.kayakapp.adapters.AirlinesAdapter;
import com.boom.kayakapp.controllers.AppController;
import com.boom.kayakapp.fragment.AirlinesFragment;
import com.boom.kayakapp.fragment.FavoriteFragment;
import com.boom.kayakapp.model.Airlines;
import com.boom.kayakapp.util.SharedPreference;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends ActionBarActivity {

        private Fragment contentFragment;
        AirlinesFragment airlinesFragment;
        FavoriteFragment favoriteFragment;

        // JSON Node names
        public static final String TAG_NAME = "name";
        public static final String TAG_PHONE = "phone";
        public static final String TAG_SITE = "site";
        public static final String TAG_LOGO = "logoURL";
        public static final String TAG_CODE = "code";

        // Log tag
        private static final String TAG = MainActivity.class.getSimpleName();

        // Airlines json url
        private static final String url = "https://www.kayak.com/h/mobileapis/directory/airlines";

        public ProgressDialog pDialog;
        public List<Airlines> airlinesList = new ArrayList<Airlines>();
        public ListView listView;
        public AirlinesAdapter adapter;

    Activity activity;
    SharedPreference sharedPreference;

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

            sharedPreference = new SharedPreference();

            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);

        listView = (ListView) findViewById(R.id.list);
        adapter = new AirlinesAdapter(this, airlinesList);
        listView.setAdapter(adapter);

        pDialog = new ProgressDialog(this);
        // Showing progress dialog before making http request
        pDialog.setMessage("Loading...");
        pDialog.show();

        // Listview on item click listener
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                // getting values from selected ListItem
                String name = ((TextView) view.findViewById(R.id.name))
                        .getText().toString();
                String phone = ((TextView) view.findViewById(R.id.phone))
                        .getText().toString();
                String site = ((TextView) view.findViewById(R.id.site))
                        .getText().toString();
                String logoURL = String.valueOf(((ImageView) view.findViewById(R.id.logoURL)));

                // Starting single contact activity
                Intent in = new Intent(getApplicationContext(),
                        SingleContactActivity.class);
                in.putExtra(TAG_NAME, name);
                in.putExtra(TAG_PHONE, phone);
                in.putExtra(TAG_SITE, site);
                in.putExtra(TAG_LOGO, logoURL);
                startActivity(in);

            }
        });

            listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener(){
                @Override
                public boolean onItemLongClick(AdapterView<?> parent, View view,
                                               int position, long id) {
                    ImageView button = (ImageView) view.findViewById(R.id.favorite_button);

                    String tag = button.getTag().toString();
                    if (tag.equalsIgnoreCase("grey")) {
                        sharedPreference.addFavorite(activity, airlinesList.get(position));
                        Toast.makeText(activity,
                                activity.getResources().getString(R.string.add_favr),
                                Toast.LENGTH_SHORT).show();

                        button.setTag("red");
                        button.setImageResource(R.drawable.heart_red);
                    } else {
                        sharedPreference.removeFavorite(activity, airlinesList.get(position));
                        button.setTag("grey");
                        button.setImageResource(R.drawable.heart_grey);
                        Toast.makeText(activity,
                                activity.getResources().getString(R.string.remove_favr),
                                Toast.LENGTH_SHORT).show();
                    }

                    return true;
                }
            });

        // changing action bar color
        getSupportActionBar().setBackgroundDrawable(
                new ColorDrawable(Color.parseColor("#1b1b1b")));

        // Creating volley request obj
        JsonArrayRequest airlinesReq = new JsonArrayRequest(url,
                new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hidePDialog();

                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {

                                JSONObject obj = response.getJSONObject(i);
                                Airlines airlines = new Airlines();
                                airlines.setName(obj.getString("name"));
                                airlines.setLogoURL(obj.getString("logoURL"));
                                airlines.setPhone(obj.getString("phone"));
                                airlines.setCode(obj.getInt("code"));
                                airlines.setSite(obj.getString("site"));

                                // adding airlines to array
                                airlinesList.add(airlines);

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

                        }

                        // notifying list adapter about data changes
                        // so that it renders the list view with updated data
                        adapter.notifyDataSetChanged();
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hidePDialog();

            }
        });

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(airlinesReq);

        FragmentManager fragmentManager = getSupportFragmentManager();

        /*
         * This is called when orientation is changed.
         */
        if (savedInstanceState != null) {
            if (savedInstanceState.containsKey("content")) {
                String content = savedInstanceState.getString("content");
                if (content.equals(FavoriteFragment.ARG_ITEM_ID)) {
                    if (fragmentManager.findFragmentByTag(FavoriteFragment.ARG_ITEM_ID) != null) {
                        setFragmentTitle(R.string.favorites);
                        contentFragment = fragmentManager
                                .findFragmentByTag(FavoriteFragment.ARG_ITEM_ID);
                    }
                }
            }
            if (fragmentManager.findFragmentByTag(AirlinesFragment.ARG_ITEM_ID) != null) {
                airlinesFragment = (AirlinesFragment) fragmentManager
                        .findFragmentByTag(AirlinesFragment.ARG_ITEM_ID);
                contentFragment = airlinesFragment;
            }
        } else {
            airlinesFragment = new AirlinesFragment();
            switchContent(airlinesFragment, AirlinesFragment.ARG_ITEM_ID);
        }
    }

    @Override
        public void onDestroy () {
        super.onDestroy();
        hidePDialog();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if (contentFragment instanceof FavoriteFragment) {
            outState.putString("content", FavoriteFragment.ARG_ITEM_ID);
        } else {
            outState.putString("content", AirlinesFragment.ARG_ITEM_ID);
        }
        super.onSaveInstanceState(outState);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_favorites:
                setFragmentTitle(R.string.favorites);
                favoriteFragment = new FavoriteFragment();
                switchContent(favoriteFragment, FavoriteFragment.ARG_ITEM_ID);

                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void switchContent(Fragment fragment, String tag) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        while (fragmentManager.popBackStackImmediate()) ;

        if (fragment != null) {
            FragmentTransaction transaction = fragmentManager
                    .beginTransaction();
            transaction.replace(R.id.content_frame, fragment, tag);
            //Only FavoriteFragment is added to the back stack.
            if (!(fragment instanceof AirlinesFragment)) {
                transaction.addToBackStack(tag);
            }
            transaction.commit();
            contentFragment = fragment;
        }
    }

    protected void setFragmentTitle(int resourseId) {
        setTitle(resourseId);
        getSupportActionBar().setTitle(resourseId);

    }

    /*
     * We call super.onBackPressed(); when the stack entry count is > 0. if it
     * is instanceof ProductListFragment or if the stack entry count is == 0, then
     * we finish the activity.
     * In other words, from ProductListFragment on back press it quits the app.
     */
    @Override
    public void onBackPressed() {
        FragmentManager fm = getSupportFragmentManager();
        if (fm.getBackStackEntryCount() > 0) {
            super.onBackPressed();
        } else if (contentFragment instanceof AirlinesFragment
                || fm.getBackStackEntryCount() == 0) {
            finish();
        }
    }

    @Override
    public void onResume() {
        super.onResume();
    }
}

这是我的 SharedPref:

This is my SharedPref:

import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;

import com.boom.kayakapp.model.Airlines;
import com.google.gson.Gson;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class SharedPreference {

    public static final String PREFS_NAME = "KAYAK_APP";
    public static final String FAVORITES = "Airlines_Favorite";

    public SharedPreference() {
        super();
    }

    // This four methods are used for maintaining favorites.
    public void saveFavorites(Context context, List<Airlines> favorites) {
//      SharedPreferences settings;
//      Editor editor;

        SharedPreferences settings = context.getSharedPreferences(PREFS_NAME,
                Context.MODE_PRIVATE);
        Editor editor = settings.edit();

        Gson gson = new Gson();
        String jsonFavorites = gson.toJson(favorites);

        editor.putString(FAVORITES, jsonFavorites);

        editor.commit();
    }

    public void addFavorite(Context context, Airlines airlines) {
        List<Airlines> favorites = getFavorites(context);
        if (favorites == null)
            favorites = new ArrayList<>();
        favorites.add(airlines);
        saveFavorites(context, favorites);
    }

    public void removeFavorite(Context context, Airlines airlines) {
        ArrayList<Airlines> favorites = getFavorites(context);
        if (favorites != null) {
            favorites.remove(airlines);
            saveFavorites(context, favorites);
        }
    }

    public ArrayList<Airlines> getFavorites(Context context) {
        SharedPreferences settings;
        List<Airlines> favorites;

        settings = context.getSharedPreferences(PREFS_NAME,
                Context.MODE_PRIVATE);

        if (settings.contains(FAVORITES)) {
            String jsonFavorites = settings.getString(FAVORITES, null);
            Gson gson = new Gson();
            Airlines[] favoriteItems = gson.fromJson(jsonFavorites,
                    Airlines[].class);

            favorites = Arrays.asList(favoriteItems);
            favorites = new ArrayList<>(favorites);
        } else
            return null;

        return (ArrayList<Airlines>) favorites;
    }
}

推荐答案

你从来没有初始化你的成员变量 activity，所以你最终为 传递了一个 null 值>Context 到 addFavorite() - 完全删除 activity 并使用 MainActivity.this (这是对 您当前所在的活动).

You never initialize your member variable activity, so you end up passing a null value for Context to addFavorite() - remove activity entirely and use MainActivity.this (which is a reference to the Activity you are currently in).

这篇关于尝试调用虚拟方法 'android.content.SharedPreferences android.content.Context.getSharedPreferences的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！