Application crashes when it remains in background for long time

Question

I'm developing Android app which is working fine. but the problem is when I navigate to another app in my device my current app goes in background. after some time when I resume that app it crashes. I don't see any problem. please help me out.

My log is as below

01-13 15:02:38.520: E/AndroidRuntime(15875): FATAL EXCEPTION: main
01-13 15:02:38.520: E/AndroidRuntime(15875):java.lang.RuntimeException:Unable to start activity ComponentInfo{shoppy.online.com/shoppy.online.com.HomeFragment}: java.lang.NullPointerException
01-13 15:02:38.520: E/AndroidRuntime(15875):at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
01-13 15:02:38.520: E/AndroidRuntime(15875):at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2416)
01-13 15:02:38.520: E/AndroidRuntime(15875):at android.app.ActivityThread.access$600(ActivityThread.java:174)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1382)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.os.Handler.dispatchMessage(Handler.java:107)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.os.Looper.loop(Looper.java:194)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.app.ActivityThread.main(ActivityThread.java:5409)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at java.lang.reflect.Method.invokeNative(Native Method)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at java.lang.reflect.Method.invoke(Method.java:525)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at dalvik.system.NativeStart.main(Native Method)
01-13 15:02:38.520: E/AndroidRuntime(15875): Caused by: java.lang.NullPointerException
01-13 15:02:38.520: E/AndroidRuntime(15875):    at shoppy.online.com.cart_db.Cart_DB.getAllItems(Cart_DB.java:39)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at shoppy.online.com.MainActivity.getCartData(MainActivity.java:677)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at shoppy.online.com.MainActivity.onCreate(MainActivity.java:103)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at shoppy.online.com.HomeFragment.onCreate(HomeFragment.java:112)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.app.Activity.performCreate(Activity.java:5122)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150)
01-13 15:02:38.520: E/AndroidRuntime(15875):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2328)
01-13 15:02:38.520: E/AndroidRuntime(15875):    ... 11 more

as it says NullPointerException on Caet_DB here is my class.

package shoppy.online.com.cart_db;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class Cart_DB {

public static SQLiteDatabase mDatabase;
public static String CREATE_CART_TABLE;
public static String CART_TABLE = "cart";
public static Cart_model[] cartData;

public static void CreateAllToDoTable() {
    createTodoTable();
}

private static void createTodoTable() {
    try {
        Cart_DB.CREATE_CART_TABLE = "CREATE TABLE IF NOT EXISTS "
                + Cart_DB.CART_TABLE + "("
                + "id INTEGER PRIMARY KEY AUTOINCREMENT,"
                + "productID TEXT," + "productName TEXT,"
                + "productPrice TEXT," + "productSellingPrice TEXT,"
                + "productDiscount TEXT," + "productQty TEXT,"
                + "shippingCharge TEXT," + "productDeliDays TEXT,"
                + "productCode TEXT," + "storeName TEXT,"
                + "productAvgRates TEXT," + "productImage TEXT,"
                + "productSlug TEXT," + "finalQty TEXT,"
                + "finalShip TEXT," + "productColorID TEXT,"
                + "productColor TEXT," + "productSizeID TEXT,"
                + "productSize TEXT," + "productStock TEXT" + ")";
        Cart_DB.mDatabase.execSQL(Cart_DB.CREATE_CART_TABLE);
    } catch (Exception e) {
    }
}

public static Cart_model[] getAllItems() {
    Cursor c = mDatabase.query(CART_TABLE, null, null, null, null, null,
            null);
    cartData = new Cart_model[c.getCount()];
    c.moveToFirst();

    int i = 0;
    while (c.isAfterLast() == false) {
        cartData[i] = new Cart_model();
        cartData[i].setID(c.getInt(0));
        cartData[i].setProductID(c.getString(1));
        cartData[i].setProductName(c.getString(2));
        cartData[i].setProductPrice(c.getString(3));
        cartData[i].setProductSellingPrice(c.getString(4));
        cartData[i].setProductDiscount(c.getString(5));
        cartData[i].setProductQty(c.getString(6));
        cartData[i].setShippingCharge(c.getString(7));
        cartData[i].setProductDeliDays(c.getString(8));
        cartData[i].setProductCode(c.getString(9));
        cartData[i].setStoreName(c.getString(10));
        cartData[i].setProductAvgRates(c.getString(11));
        cartData[i].setProductImage(c.getString(12));
        cartData[i].setProductSlug(c.getString(13));
        cartData[i].setFinalQty(c.getString(14));
        cartData[i].setFinalShip(c.getString(15));
        cartData[i].setProductColorID(c.getString(16));
        cartData[i].setProductColor(c.getString(17));
        cartData[i].setProductSizeID(c.getString(18));
        cartData[i].setProductSize(c.getString(19));
        cartData[i].setProductStock(c.getString(20));
        i++;
        c.moveToNext();
    }
    return cartData;
}

public static void insertAllCart(String productID, String productName,
        String productPrice, String productSellingPrice,
        String productDiscount, String productQty, String shippingCharge,
        String productDeliDays, String productCode, String storeName,
        String productAvgRates, String productImage, String productSlug,
        String finalQty, String finalShip, String productColorID,
        String productColor, String productSizeID, String productSize,
        String productStock) {
    ContentValues val = new ContentValues();
    val.put("productID", productID);
    val.put("productName", productName);
    val.put("productPrice", productPrice);
    val.put("productSellingPrice", productSellingPrice);
    val.put("productDiscount", productDiscount);
    val.put("productQty", productQty);
    val.put("shippingCharge", shippingCharge);
    val.put("productDeliDays", productDeliDays);
    val.put("productCode", productCode);
    val.put("storeName", storeName);
    val.put("productAvgRates", productAvgRates);
    val.put("productImage", productImage);
    val.put("productSlug", productSlug);
    val.put("finalQty", finalQty);
    val.put("finalShip", finalShip);
    val.put("productColorID", productColorID);
    val.put("productColor", productColor);
    val.put("productSizeID", productSizeID);
    val.put("productSize", productSize);
    val.put("productStock", productStock);

    @SuppressWarnings("unused")
    long value = mDatabase.insert(CART_TABLE, null, val);
}

public static void updateCartData(Cart_model c) {
    ContentValues value = new ContentValues();
    value.put("productID", c.productID);
    value.put("productName", c.productName);
    value.put("productPrice", c.productPrice);
    value.put("productSellingPrice", c.productSellingPrice);
    value.put("productDiscount", c.productDiscount);
    value.put("productQty", c.productQty);
    value.put("shippingCharge", c.shippingCharge);
    value.put("productDeliDays", c.productDeliDays);
    value.put("productCode", c.productCode);
    value.put("storeName", c.storeName);
    value.put("productAvgRates", c.productAvgRates);
    value.put("productImage", c.productImage);
    value.put("productSlug", c.productSlug);
    value.put("finalQty", c.finalQty);
    value.put("finalShip", c.finalShip);
    value.put("productColorID", c.productColorID);
    value.put("productColor", c.productColor);
    value.put("productSizeID", c.productSizeID);
    value.put("productSize", c.productSize);
    value.put("productStock", c.productStock);
    mDatabase.update(CART_TABLE, value, "id = " + c.ID, null);
}

public static void deleteCartData(Cart_model d) {
    mDatabase.delete(CART_TABLE, "id = " + d.ID, null);
}
}

MainActivity

public class MainActivity extends AppCompatActivity implements OnClickListener {
protected FrameLayout frameLayout;
protected DrawerLayout mDrawerLayout;
protected ListView mDrawerList;
protected ActionBarDrawerToggle mDrawerToggle;
protected static int position;
protected static boolean isLaunch = true;

Toolbar toolbar;

RelativeLayout prof_head;
protected TextView profile_name, track_order;
protected TextView login;
TextView contact_us;
TextView faqs;
TextView about_us;
TextView tvChar;
protected RoundedImageView img;
protected FrameLayout fam;

private CharSequence mTitle;

private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

SharedPreferences sharedPreferences;
protected String MyPREFERENCES = "MyPrefs";
public static String name, pass, uname, pImg;
public static String id;
public static ArrayList<Cart_model> listdata;
public static ArrayList<Wishlist_model> listdata1;
Cart_model[] data;
Bundle kek;

@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    kek = savedInstanceState;
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    frameLayout = (FrameLayout) findViewById(R.id.frame_container);
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    toolbar = (Toolbar) findViewById(R.id.toolbar_headers);

    setSupportActionBar(toolbar);
    getCartData();
    getWishData();

    LayoutInflater inflater = getLayoutInflater();
    View listHeaderView = inflater.inflate(R.layout.profile_header, null,
            false);
    View listFooterView = inflater
            .inflate(R.layout.nav_footer, null, false);
    mDrawerList.addHeaderView(listHeaderView);
    mDrawerList.addFooterView(listFooterView);

    navDrawerItems = new ArrayList<NavDrawerItem>();

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons
            .getResourceId(0, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons
            .getResourceId(1, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons
            .getResourceId(2, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons
            .getResourceId(3, -1), true, "22"));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons
            .getResourceId(4, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons
            .getResourceId(5, -1), true, "50+"));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons
            .getResourceId(6, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[7], navMenuIcons
            .getResourceId(7, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[8], navMenuIcons
            .getResourceId(8, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[9], navMenuIcons
            .getResourceId(9, -1), true, "22"));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[10], navMenuIcons
            .getResourceId(10, -1)));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[11], navMenuIcons
            .getResourceId(11, -1), true, "50+"));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[12], navMenuIcons
            .getResourceId(12, -1), true, "50+"));
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[13], navMenuIcons
            .getResourceId(13, -1), true, "50+"));

    navMenuIcons.recycle();

    mDrawerList.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            displayView(position);
        }
    });

    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);
    mDrawerList.setItemChecked(1, true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            R.drawable.ic_drawer, R.string.app_name) {
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    // mDrawerToggle.setDrawerIndicatorEnabled(false);

    if (isLaunch) {
        isLaunch = false;
        displayView(1);
    }

    sharedPreferences = getSharedPreferences(MyPREFERENCES,
            Context.MODE_PRIVATE);
    id = sharedPreferences.getString("id", null);
    name = sharedPreferences.getString("email", null);
    uname = sharedPreferences.getString("name", null);
    pass = sharedPreferences.getString("password", null);
    pImg = sharedPreferences.getString("profileImg", null);

    prof_head = (RelativeLayout) findViewById(R.id.prof_head);
    prof_head.setOnClickListener(this);
    profile_name = (TextView) findViewById(R.id.profile_name);
    img = (RoundedImageView) findViewById(R.id.roundedImage);
    fam = (FrameLayout) findViewById(R.id.flProfil);
    tvChar = (TextView) findViewById(R.id.tvChar);
    track_order = (TextView) findViewById(R.id.track_order);
    track_order.setOnClickListener(this);
    login = (TextView) findViewById(R.id.login);
    login.setOnClickListener(this);
    contact_us = (TextView) findViewById(R.id.contact_us);
    contact_us.setOnClickListener(this);
    faqs = (TextView) findViewById(R.id.faqs);
    faqs.setOnClickListener(this);
    about_us = (TextView) findViewById(R.id.about_us);
    about_us.setOnClickListener(this);

    int status = 0;
    int resourceId = getResources().getIdentifier("status_bar_height",
            "dimen", "android");
    if (resourceId > 0) {
        status = getResources().getDimensionPixelSize(resourceId);
    }

    float scale = getResources().getDisplayMetrics().density;
    int paddingdp = (int) (16 * scale + 0.5f);
    int heightdp = 0;
    if ((getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) == Configuration.SCREENLAYOUT_SIZE_LARGE) {
        heightdp = (int) (200 * scale + 0.5f);

    } else {
        heightdp = (int) (130 * scale + 0.5f);
    }

    // int statusbar = (int) (25 * scale + 0.5f);

    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
        toolbar.setPadding(0, status, 0, 0);
        // listHeaderView.setPadding(32, 84, 32, 32);
        prof_head.setPadding(paddingdp, paddingdp + status, paddingdp,
                paddingdp);
        LayoutParams params = (LayoutParams) prof_head.getLayoutParams();
        params.height = heightdp + status;
        prof_head.setLayoutParams(params);
    } else {
    }

    if (name.equals("user_email")) {
        login.setText("Login");
        profile_name.setText("Welcome User");
        img.setVisibility(View.VISIBLE);
        img.setImageResource(R.drawable.images);
        fam.setVisibility(View.GONE);
    } else if (!name.equals("user_email")) {
        login.setText("Logout");
        profile_name.setText(name);
        if (pImg.equals("")) {
            fam.setVisibility(View.VISIBLE);
            img.setVisibility(View.GONE);
            String tag = (String) name.subSequence(0, 1);
            tvChar.setText(tag);
        } else {
            Picasso.with(getApplicationContext()).load(pImg).into(img);
        }
    }

}

Answer 1

After lots of debugging finally solved this issue. as @fasteque pointed out I was initiating mDatabase in My starting screen.

so I've did some minor changes in MainActivity and now it is working like charm.

Here are my changes

if (Cart_DB.mDatabase == null) {
        Cart_DB.mDatabase = openOrCreateDatabase("CART",
                SQLiteDatabase.CREATE_IF_NECESSARY, null);
}

if (Wishlist_DB.mDatabase == null) {
        Wishlist_DB.mDatabase = openOrCreateDatabase("WISHLIST",
                SQLiteDatabase.CREATE_IF_NECESSARY, null);
}