应用程序在长时间处于后台时崩溃
问题描述：
我正在开发可正常工作的Android应用程序。但问题是当我导航到我的设备中的另一个应用程序我当前的应用程序在后台。一段时间后，我恢复该应用程序崩溃。我没有看到任何问题。请帮助我。应用程序在长时间处于后台时崩溃
我的日志如下
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
，因为它说NullPointerException上Caet_DB这里是我的课。
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);
}
}
}
答
经过大量的调试终于解决了这个问题。因为@fasteque指出我在我的开始屏幕中启动了mDatabase。
所以我在MainActivity做了一些小的改动，现在它像魅力一样工作。
这里是我的变化
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);
}
您是否使用与'HomeFragment'参数的构造函数？也可以从'MainActivity'上放置'onCreate'的代码 – LordRaydenMK
您还可以具体说明NPE出现的确切代码行吗？谢谢！ – fasteque
@fasteque at'Cursor c = mDatabase.query（CART_TABLE，null，null，null，null，null，null）;' –