这是我作为错误得到的堆栈跟踪:
Process: com.peems.itcrowd, PID: 2949 java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:873) at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:215) at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1481) at android.view.View.dispatchRestoreInstanceState(View.java:15751) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3231) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3237) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3237) at android.view.View.restoreHierarchyState(View.java:15729) at android.support.v4.app.Fragment.restoreViewState(Fragment.java:475) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1329) at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595) at android.support.v4.app.BackStackRecord.executePopOps(BackStackRecord.java:803) at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2353) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2146) at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2008) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
我将解释我是如何得到这个错误的。
在我的 fragment 中，我调用了这个方法，然后它将通过我的 Activity 并启动另一个包含 viewpager 的 fragment 。
@Override
public void checkoutCartResult(Result<Shop> result) {
mShop = result.getData();
sendActionToActivity(ACTION_ORDER, mShop);
DisplayUtil.doToast(getContext(), getString(R.string.checkout_successful));
}
private void sendActionToActivity(String action, Shop shop) {
if (mListener == null) {
return;
}
Bundle bundle = new Bundle();
bundle.putString(Constants.ACTION_KEY, action);
bundle.putParcelable(Constants.DATA_KEY_1, Parcels.wrap(shop));
mListener.onFragmentInteraction(bundle);
}
上面的方法将触发这个 fragment :
public class ShopFragment extends BaseFragment implements ShopView,
ViewPager.OnPageChangeListener {
private static final String TAG = ShopFragment.class.getName();
private static final String ARG_PARAM1 = "param1";
FragmentShopBinding mBinder;
Shop mShop;
ShopPresenter mPresenter;
ShopAdapter mAdapter;
PreferenceAdapter mPreferenceAdapter;
LayerDrawable mCartMenuIcon;
List<String> mTabTitles;
String mImagePath;
boolean isProductsShown = false;
public ShopFragment() {
// Required empty public constructor
}
public static ShopFragment newInstance(Shop shop) {
ShopFragment fragment = new ShopFragment();
Bundle args = new Bundle();
args.putParcelable(ARG_PARAM1, Parcels.wrap(shop));
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
if (getArguments() != null) {
Parcelable parcelable;
parcelable = getArguments().getParcelable(ARG_PARAM1);
mShop = Parcels.unwrap(parcelable);
}
mTabTitles = new ArrayList<>(4);
mTabTitles.add(getString(R.string.wishlist_fragment));
mTabTitles.add(getString(R.string.history_fragment));
mTabTitles.add(getString(R.string.offers_fragment));
mTabTitles.add(getString(R.string.products_fragment));
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mBinder = DataBindingUtil.inflate(inflater, R.layout.fragment_shop, container, false);
mBinder.tabs.setTabMode(TabLayout.MODE_FIXED);
mBinder.tabs.setTabGravity(TabLayout.GRAVITY_FILL);
mAdapter = new ShopAdapter(getChildFragmentManager(), mTabTitles, mShop);
mPreferenceAdapter = new PreferenceAdapter(getContext());
mBinder.viewpager.setAdapter(mAdapter);
mBinder.viewpager.addOnPageChangeListener(this);
checkForImage();
mBinder.tabs.setupWithViewPager(mBinder.viewpager);
mPresenter = new ShopPresenterImpl(this);
((MainActivity) getActivity()).setActionBarTitle(mShop.getName());
EventBus.getDefault().register(this);
return mBinder.getRoot();
}
@Override
public void onDestroyView() {
super.onDestroyView();
EventBus.getDefault().unregister(this);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
//show cart items in badge
mCartMenuIcon = (LayerDrawable) menu.findItem(R.id.action_cart).getIcon();
setBadgeCount(mCartMenuIcon, String.valueOf(mShop.getCartItems()));
// show/hide login icon
if (mShop.getLoginId() == -1) {
menu.findItem(R.id.action_login).setVisible(true);
menu.findItem(R.id.action_logout).setVisible(false);
} else {
menu.findItem(R.id.action_login).setVisible(false);
menu.findItem(R.id.action_logout).setVisible(true);
}
super.onCreateOptionsMenu(menu, inflater);
}
@Override
protected void setTypeface() {
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
DisplayUtil.hideKeyboard(ShopFragment.this.getActivity());
}
@Override
public void onPageSelected(int position) {
String pageTitle;
pageTitle = mAdapter.getPageTitle(position).toString();
isProductsShown = pageTitle.equals(getString(R.string.products_fragment));
ShopFragment.this.getActivity().invalidateOptionsMenu();
//reloadData(position);
}
@Override
public void onPageScrollStateChanged(int state) {
}
@Override
public void logoutShop(Shop shop) {
}
@Override
public void showError(Error error) {
DisplayUtil.okDialog(getContext(), error.getErrorTitle(), error.getErrorMessage(), new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
}
@Override
public void showProgress(boolean show) {
}
private void sendActionToActivity(String action) {
if (mListener == null) {
return;
}
Bundle bundle = new Bundle();
bundle.putString(Constants.ACTION_KEY, action);
mListener.onFragmentInteraction(bundle);
}
private void logoutShop() {
AsyncExecutor.create().execute(new AsyncExecutor.RunnableEx() {
@Override
public void run() throws Exception {
mPresenter.logoutShop(mShop);
ShopRepository shopRepository;
shopRepository = new ShopRepository();
mShop.setLoginId(-1);
mShop.setCustomerId(-1);
mShop.setCartNumber(0);
mShop.setLineNumber(0);
mShop.setCartItems(0);
shopRepository.updateLoginNumber(mShop);
shopRepository.updateCart(mShop);
notifyChanges();
}
});
}
public void logoutDialog() {
DisplayUtil.logoutDialog(getContext(), getString(R.string.action_log_out), getString(R.string.are_you_sure),
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
logoutShop();
}
}, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
}
private void setBadgeCount(LayerDrawable icon, String count) {
BadgeDrawable badge;
// Reuse drawable if possible
Drawable reuse = icon.findDrawableByLayerId(R.id.ic_badge);
if (reuse != null && reuse instanceof BadgeDrawable) {
badge = (BadgeDrawable) reuse;
} else {
badge = new BadgeDrawable(getContext());
}
badge.setCount(count);
icon.mutate();
icon.setDrawableByLayerId(R.id.ic_badge, badge);
}
private void notifyChanges() {
AuthShopResult event;
event = new AuthShopResult();
event.setShop(mShop);
EventBus.getDefault().post(event);
}
private void checkForImage() {
mImagePath = mPreferenceAdapter.readImagePathMax();
if (mImagePath.equals("")) {
mBinder.viewpager.setOffscreenPageLimit(4);
}
}
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessage(LoadCartNumber event) {
mShop = event.getShop();
}
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessage(AuthShopResult event) {
mShop = event.getShop();
// hide Login option menu
if (getActivity() != null) {
getActivity().invalidateOptionsMenu();
}
}
}
这是执行所有事务的 Activity 。
public class MainActivity extends AppCompatActivity implements
BaseFragment.OnFragmentInteractionListener,
BaseDialogFragment.OnFragmentInteractionListener,
FragmentManager.OnBackStackChangedListener {
private static final String CURRENT_FRAGMENT = "current_fragment";
private static final String CURRENT_PEEM_ID = "current_peem_id";
private static final String CURRENT_SHOP_ID = "current_shop_id";
private static final String CURRENT_CART_NUMBER = "current_cart_number";
private static final String CURRENT_CART_LINE = "current_cart_line";
private static final String CURRENT_CART_ITEMS = "current_cart_items";
public ActivityMainBinding mBinder;
private Peem mCurrentPeem;
private Shop mCurrentShop;
private Fragment mFragment;
private DialogFragment mDialogFragment;
private PreferenceAdapter mPreferenceAdapter;
private int mFragmentBackStackCounter = 0;
private int languagePosition;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//LeakCanary.install(getApplication());
mBinder = DataBindingUtil.setContentView(this, R.layout.activity_main);
setSupportActionBar(mBinder.toolbar);
showActionBar(true);
mPreferenceAdapter = new PreferenceAdapter(App.getContext());
getSupportFragmentManager().addOnBackStackChangedListener(MainActivity.this);
}
@Override
protected void onPostCreate(@Nullable Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
EventBus.getDefault().register(this);
if (savedInstanceState != null) {
mFragment = getSupportFragmentManager().getFragment(savedInstanceState, CURRENT_FRAGMENT);
PeemRepository peemRepository = new PeemRepository();
ShopRepository shopRepository = new ShopRepository();
try {
Peem peem;
int peemId = savedInstanceState.getInt(CURRENT_PEEM_ID);
peem = peemRepository.findById(peemId);
mCurrentPeem = peem;
} catch (SQLException e) {
e.printStackTrace();
}
try {
Shop shop;
int shopId = savedInstanceState.getInt(CURRENT_SHOP_ID);
shop = shopRepository.findById(shopId);
mCurrentShop = shop;
if (mCurrentShop != null && mCurrentShop.getLoginId() == -1) {
mCurrentShop.setCartNumber(savedInstanceState.getInt(CURRENT_CART_NUMBER));
mCurrentShop.setLineNumber(savedInstanceState.getInt(CURRENT_CART_LINE));
mCurrentShop.setCartItems(savedInstanceState.getInt(CURRENT_CART_ITEMS));
}
} catch (SQLException e) {
e.printStackTrace();
}
} else {
if (isUserLoggedIn()) {
checkFavourite();
} else {
fragmentManager(RegisterFragment.newInstance());
}
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
if (getCurrentFragment() == null) {
getSupportFragmentManager().putFragment(outState, CURRENT_FRAGMENT, mFragment);
} else {
mFragment = getCurrentFragment();
getSupportFragmentManager().putFragment(outState, CURRENT_FRAGMENT, mFragment);
}
if (mCurrentPeem != null) {
int peemId = mCurrentPeem.getId();
outState.putInt(CURRENT_PEEM_ID, peemId);
}
if (mCurrentShop != null) {
int shopId = mCurrentShop.getId();
int cartNumber = mCurrentShop.getCartNumber();
int cartLineNumber = mCurrentShop.getLineNumber();
int cartItems = mCurrentShop.getCartItems();
outState.putInt(CURRENT_SHOP_ID, shopId);
outState.putInt(CURRENT_CART_NUMBER, cartNumber);
outState.putInt(CURRENT_CART_LINE, cartLineNumber);
outState.putInt(CURRENT_CART_ITEMS, cartItems);
}
super.onSaveInstanceState(outState);
}
@Override
protected void onDestroy() {
super.onDestroy();
getSupportFragmentManager().removeOnBackStackChangedListener(com.peems.itcrowd.ui.activity.MainActivity.this);
EventBus.getDefault().unregister(this);
mFragment = null;
mDialogFragment = null;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_ab, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_back_to_peem:
mFragment = PeemFragment.newInstance();
getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, mFragment, Integer.toString(getFragmentCount()))
.addToBackStack(null)
.commit();
return true;
case R.id.action_back_to_shop:
mFragment = ShopListFragment.newInstance(mCurrentPeem);
getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, mFragment, Integer.toString(getFragmentCount()))
.addToBackStack(null)
.commit();
return true;
default:
// If we got here, the user's action was not recognized.
// Invoke the superclass to handle it.
return super.onOptionsItemSelected(item);
}
}
@Override
public void onFragmentInteraction(Bundle arg) {
String action;
action = arg.getString(Constants.ACTION_KEY);
if (action.equals(OrderSummaryFragment.ACTION_ORDER)) {
Shop shop;
Parcelable parcelable;
parcelable = arg.getParcelable(Constants.DATA_KEY_1);
shop = Parcels.unwrap(parcelable);
fragmentManager(ShopFragment.newInstance(shop));
return;
}
if (action.equals(OrderSummaryFragment.ACTION_HIDE_ACTION_BAR)) {
showActionBar(false);
return;
}
if (action.equals(OrderSummaryFragment.ACTION_SHOW_ACTION_BAR)) {
showActionBar(true);
return;
}
}
private void fragmentManager(Fragment fragment) {
if (fragment instanceof PeemFragment) {
mFragment = fragment;
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, fragment, Integer.toString(getFragmentCount()))
.addToBackStack(PeemFragment.class.getSimpleName())
.commit();
return;
}
if (fragment instanceof ShopFragment) {
mFragment = fragment;
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, fragment, Integer.toString(getFragmentCount()))
.addToBackStack(ShopFragment.class.getSimpleName())
.commit();
return;
}
if (fragment instanceof ShopListFragment) {
mFragment = fragment;
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, fragment, Integer.toString(getFragmentCount()))
.addToBackStack(ShopListFragment.class.getSimpleName())
.commit();
return;
}
if (fragment instanceof OrderSummaryFragment) {
mFragment = fragment;
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, fragment, Integer.toString(getFragmentCount()))
.addToBackStack(OrderSummaryFragment.class.getSimpleName())
.commit();
return;
}
}
protected int getFragmentCount() {
return getSupportFragmentManager().getBackStackEntryCount();
}
private Fragment getFragmentAt(int index) {
return getFragmentCount() > 0 ? getSupportFragmentManager().findFragmentByTag(Integer.toString(index)) : null;
}
protected Fragment getCurrentFragment() {
return getFragmentAt(getFragmentCount() - 1);
}
@Override
public void onBackPressed() {
// still not defined behavior
if (mFragmentBackStackCounter > 0) {
getSupportFragmentManager().popBackStack();
} else if (mFragmentBackStackCounter == 0) {
finish();
}
}
@Override
public void onBackStackChanged() {
int entryCount = getSupportFragmentManager().getBackStackEntryCount() - 1;
mFragmentBackStackCounter = entryCount;
if (entryCount >= 0) {
FragmentManager.BackStackEntry backStackEntry;
backStackEntry = getSupportFragmentManager().getBackStackEntryAt(entryCount);
/*if(mFragmentBackStackCounter > entryCount){
mFragment = getSupportFragmentManager().findFragmentByTag(backStackEntry.getName());
}*/
mFragmentBackStackCounter = entryCount;
}
}
private void showActionBar(boolean state) {
ActionBar actionBar;
actionBar = getSupportActionBar();
/*if (actionBar != null) {
actionBar.setTitle("SHOP");*/
if (state) {
if (actionBar != null) {
actionBar.show();
}
} else {
if (actionBar != null) {
actionBar.hide();
}
}
}
private boolean isUserLoggedIn() {
String accessToken;
boolean isLoggedIn = true;
accessToken = mPreferenceAdapter.readAccessToken();
if (accessToken.isEmpty()) {
isLoggedIn = false;
}
return isLoggedIn;
}
}
这是 ShopFragment 的 viewpager:
public class ShopAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
private final List<String> mTabTitles;
Shop mShop;
public enum TAB {
WISHLIST(0), HISTORY(1), OFFERS(2), PRODUCTS(3);
int value;
TAB(int i) {
this.value = i;
}
public int getValue() {
return value;
}
}
public ShopAdapter(FragmentManager fm, List<String> tabTitles, Shop shop) {
super(fm);
this.mTabTitles = tabTitles;
this.mNumOfTabs = tabTitles.size();
this.mShop = shop;
}
public void addTitle(String title) {
mTabTitles.add(title);
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return WishlistTabFragment.newInstance(mShop);
case 1:
return HistoryTabFragment.newInstance(mShop);
case 2:
return OffersTabFragment.newInstance(mShop);
case 3:
return ProductsFragment.newInstance(mShop);
default:
return null;
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
@Override
public CharSequence getPageTitle(int position) {
reloadData(position);
return mTabTitles.get(position);
}
@Override
public int getItemPosition(Object object) {
return super.getItemPosition(object);
}
private void reloadData(int position) {
RefreshResult result = new RefreshResult();
result.setPageNumber(position);
EventBus.getDefault().post(result);
}
}
所以导致这个错误的场景如下:
我调用 sendActionToActivity(ACTION_ORDER, mShop);，现在我在 ShopFragment 中。当我在那里时，我可以看到带有一个项目的工具栏，当我点击它时会在我的 Activity 中调用这个方法:
case R.id.action_back_to_shop:
mFragment = ShopListFragment.newInstance(mCurrentPeem);
getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_holder, mFragment, Integer.toString(getFragmentCount()))
.addToBackStack(null)
.commit();
return true;
那就是错误发生的时候。如果我执行此方案但未调用 sendActionToActivity(ACTION_ORDER, mShop);，则一切正常。
最佳答案
以防其他人遇到此问题，我已将我的 FragmentStatePagerAdapter 更改为 FragmentPagerAdapter，它成功了。但是，如果您想使用 FragmentStatePagerAdapter，可能会修复此 link ，人们遇到了这个问题。
关于android - 没有迹象表明 NPE 可能发生在哪里，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42213051/