Develop Reference

App crashes when launched in debugging on setUserVisibleHint()

If I ran the app normally it would work just fine,when I put a breakpoint on if statement in setUserVisibleHint(),it crashes with exception: java.lang.IllegalStateException: No activity.
So what's gonna be the problem?
public class MyFragment extends Fragment
public MyFragment() {
// Required empty public constructor
}
public static CommunityFragment newInstance() {
Bundle args = new Bundle();
MyFragment fragment = new MyFragment();
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_community, container, false);
}
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (getActivity() != null && isVisibleToUser) {
// fragment is visible
}
} else if (getActivity() != null) {
// fragment is invisible
}
}
}
}
logcat:
E/AndroidRuntime: FATAL EXCEPTION: main
PID: 8669
java.lang.IllegalStateException: No activity
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1578)
at android.support.v4.app.FragmentManagerImpl.dispatchCreate(FragmentManager.java:2883)
at android.support.v4.app.Fragment.onCreate(Fragment.java:1268)
at android.support.v4.app.Fragment.performCreate(Fragment.java:2177)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1244)
at android.support.v4.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1080)
at android.support.v4.app.FragmentTransition.calculateFragments(FragmentTransition.java:971)
at android.support.v4.app.FragmentTransition.startTransitions(FragmentTransition.java:95)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2143)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1979)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:626)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1268)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:714)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:786)
at android.view.View.measure(View.java:18788)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android

Instead of
if (getActivity() != null && isVisibleToUser) {
// fragment is visible
}
} else if (getActivity() != null) {
// fragment is invisible
}
try with
if (getView() != null) {
// fragment is visible
}
It worked for me.

RecyclerView error ConcurrentModificationException only API 23 & API 26

I get ConcurrentModificationException in my RecyclerView, only in APIs 23 & 26, how can I bypass this?
This is my RecyclerView Setup:
private void setUpRecyclerView() {
int maxIndex = 0;
if (game.size() < 3) {
maxIndex = game.size();
} else if (game.size() >= 3) {
maxIndex = 3;
}
recyclerView = findViewById(R.id.home_recycler_view);
adapter = new GameCardListMiniAdapter(this, game.subList(0, maxIndex));
recyclerView.setAdapter(adapter);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(ActivityHome.this);
linearLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
}
after I manipulate the data from game, I call recyclerView.swapAdapter(adapter, true); and get the error, but only in the afore mentioned APIs, in the rest of the APIs up to API 15 everything works just fine.
This is the stacktrace for API 23:
E/Surface: getSlotFromBufferLocked: unknown buffer: 0xa0d2a5a0
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.racu.cardgame, PID: 26900
java.util.ConcurrentModificationException
at java.util.AbstractList$SubAbstractList.size(AbstractList.java:360)
at com.example.racu.cardgame.adapters.cardgameListMiniAdapter.getItemCount(cardgameListMiniAdapter.java:68)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3603)
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3103)
at android.view.View.measure(View.java:18788)
at android.support.v4.widget.NestedScrollView.measureChildWithMargins(NestedScrollView.java:1446)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v4.widget.NestedScrollView.onMeasure(NestedScrollView.java:512)
at android.view.View.measure(View.java:18788)
at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)
at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)
at android.view.View.measure(View.java:18788)
at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)
at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1060)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygot
This is for API 26:
D/EGL_emulation: eglMakeCurrent: 0x9d2e70a0: ver 2 0 (tinfo 0xa8e8b510)
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.racu.cardgame, PID: 4691
java.util.ConcurrentModificationException
at java.util.ArrayList$SubList.size(ArrayList.java:1057)
at com.example.racu.cardgame.adapters.cardgameListMiniAdapter.getItemCount(cardgameListMiniAdapter.java:68)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3603)
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3103)
at android.view.View.measure(View.java:21998)
at android.support.v4.widget.NestedScrollView.measureChildWithMargins(NestedScrollView.java:1446)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v4.widget.NestedScrollView.onMeasure(NestedScrollView.java:512)
at android.view.View.measure(View.java:21998)
at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)
at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)
at android.view.View.measure(View.java:21998)
at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)
at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
at android.view.View.measure(View.java:21998)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1060)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
at android.view.View.measure(View.java:21998)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:721)
at android.view.View.measure(View.java:21998)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2410)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1498)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1751)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1386)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6733)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
at android.view.Choreographer.doCallbacks(Choreographer.java:723)
at android.view.Choreographer.doFrame(Choreographer.java:658)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
08-14 18:50:44.793 4691-4691/com.example.racu.cardgame E/AndroidRuntime: at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Tried to make it work creating the game.SubList outside,with a for loop instead of a SubList, didn't crash, but swapAdapter wasn't being called and the most strange thing is that is working wonderful in my phone, no crashes and the expected behavior.
I really,really apreciate some light.
Regards Ne0R#Cu

The root of this issue is that List.subList() does not copy the List:
/**
* Returns a view of the portion of this list between the specified
* fromIndex, inclusive, and toIndex, exclusive. (If
* fromIndex and toIndex are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
...
Then, when you call size() on the resulting view, the exception is thrown. I haven't dug into why this happened, but size() tries to validate it's current size, which in this case is conflicted between the full list and the view.
So, you can remedy this crash by simply copying the list:
List<YOUR_TYPE> trimmed = new ArrayList<>( game.subList(0, maxIndex) );
adapter = new GameCardListMiniAdapter(this, trimmed);

Try
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
instead of :
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(ActivityHome.this);
then do the same thing ext
rc.setHasFixedSize(false);//only use this for fixed ammount
rc.setLayoutManager(layoutManager);
rc.setAdapter(dataItemAdapter);

I could not find any answer for my question, I ended up creating a HorizontalScrollView and adding my views from code to a LinearLayout within the HorizontalScrollView.

Querying objectId of a pointer class in Parse.com - Android

I'm trying to retrieve the objectId as a string from my User class in Parse, but I'm getting a NullPointer.
Log.w(getClass().toString(), ParseUser.getCurrentUser().getParseObject("currentGroup").getObjectId());
java.lang.NullPointerException: println needs a message
I'm querying the column "currentGroup", which is a pointer to a class called "Group". All I want is to retrieve its objectId. Both the currentGroup and Group objectId columns have data. They are not null. What's going on here?
Error:
It seems to think the object is null but I can't see why it would be.
java.lang.NullPointerException: Attempt to invoke virtual method
'java.lang.String com.parse.ParseObject.getObjectId()' on a null object reference
at at com.yitter.android.fragment.FeedFragment.retrieveData(FeedFragment.java:112)
at com.yitter.android.fragment.FeedFragment.onCreateView(FeedFragment.java:105)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1638)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679)
at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:166)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1240)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1088)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614)
at android.view.View.measure(View.java:18794)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:18794)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1085)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18794)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

ParseQuery<ParseObject> query = ParseQuery.getQuery("Orders");
ParseObject obj = ParseObject.createWithoutData("ShopLocations",idd); // this pointer object class name and pointer value
query.whereEqualTo("shop", obj); // this pointer object and parse object
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> object, ParseException e) {
if (e == null) {}}
This is working correctly retrieving data from parse.

I found the solution. You can not retrieve the object of a pointer using ParseUser.getCurrentUser(). You have to do a full ParseUser query to retrieve the current User, by finding the user in your User table with an objectId equal to ParseUser.getCurrentUser().getObjectId().
ParseQuery query = ParseUser.getQuery();
query.whereEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
query.findInBackground(new FindCallback() {
#Override
public void done(List<ParseObject> users, ParseException e) {
if (e == null) for (userObject : users) {
// I retrieve the objectId from the pointer
// only after directly querying for the current User.
userObject.getParseObject("currentGroup").getObjectId();
}
}
});
At least, this is the only way I managed to get this to work in my app. I'm not sure why the .getParseObject() method is available to ParseUser.getCurrentUser() if you can't just directly retrieve the objectId of the specified pointer object, but oh well. If anyone knows, I'd love to know how you did it.

Getting null error in android tab project

Getting null error on this line
mFragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
Getting android error on below code.
DrawerLayout mDrawerLayout;
NavigationView mNavigationView;
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/**
*Setup the DrawerLayout and NavigationView
*/
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
mNavigationView = (NavigationView) findViewById(R.id.shitstuff);
/**
* Lets inflate the very first fragment
* Here , we are inflating the TabFragment as the first Fragment
*/
mFragmentManager = getSupportFragmentManager();
mFragmentTransaction = mFragmentManager.beginTransaction();
mFragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
/**
* Setup click events on the Navigation View Items.
*/
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
mDrawerLayout.closeDrawers();
if (menuItem.getItemId() == R.id.nav_item_sent) {
FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.containerView,new SentFragment()).commit();
}
if (menuItem.getItemId() == R.id.nav_item_inbox) {
FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
// xfragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
}
return false;
}
});
/**
* Setup Drawer Toggle of the Toolbar
*/
android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar);
ActionBarDrawerToggle mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, toolbar,R.string.app_name,
R.string.app_name);
mDrawerLayout.setDrawerListener(mDrawerToggle);
mDrawerToggle.syncState();
}
logcat error log
.tabproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kpgames.tabproject, PID: 22961
java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:418)
at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:413)
at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:943)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1157)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1075)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.ref

You are getting NullPointerException .
Attempt to write to field 'android.support.v4.app.FragmentManagerImpl
android.support.v4.app.Fragment.mFragmentManager' on a null object
reference
NullPointerException is thrown when an application attempts to use an
object reference that has the null value.
Check How to pass newFragment
Fragment tabFragment = new TabFragment();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack if needed
transaction.replace(R.id.fragment_container, tabFragment );
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
FYI
Call android.support.v4.app.Fragment instead of android.app.Fragment .

It was issue from my side only. i was including this to my tab fragment and was setting 2 fragment but item count set to 3. thats why its giving null issue.. thank you for help and attension

Simple ListView using Firebase on Android. Issue with JSON

I want to display a simple list of names in a list view. But I'm not able to figure out how. I think I'll not be able to use a modal class since all the values in JSON will have same property called students. My JSON data on firebase looks like this on firebse
{
"physicsClass":{
"students":["John","Frank","Allen"]
},
"chemistryClass":{
"students":["Gillen","Jason","David East"]
}
}
When I run the it crashes with the following error log:
com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.ArrayList to String
at com.google.android.gms.internal.zzaix.zzaC(Unknown Source)
at com.google.android.gms.internal.zzaix.zzb(Unknown Source)
at com.google.android.gms.internal.zzaix.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.firebase.ui.database.FirebaseListAdapter.parseSnapshot(FirebaseListAdapter.java:113)
at com.firebase.ui.database.FirebaseListAdapter.getItem(FirebaseListAdapter.java:102)
at com.firebase.ui.database.FirebaseListAdapter.getView(FirebaseListAdapter.java:130)
at android.widget.AbsListView.obtainView(AbsListView.java:2346)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1281)
at android.widget.ListView.onMeasure(ListView.java:1188)
at android.view.View.measure(View.java:18794)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18794)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18794)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Suggest any other way of implementing the above data in a list view / recycler view.
I'm using the firebase-ui sdk to display data in the listview. Below is the code
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
DatabaseReference sezRef = ref.child("physics");
studentList = (ListView)findViewById(R.id.studentList);
firebaseListAdapter = new FirebaseListAdapter<String>(this,String.class,android.R.layout.simple_list_item_1,phyRef) {
#Override
protected void populateView(View v, String model, int position) {
TextView textView = (TextView)v.findViewById(android.R.id.text1);
textView.setText(model);
}
};studentList.setAdapter(firebaseListAdapter);

The error Failed to convert value of type means that when you retrieve you object from Firebase snapshot, you try to get the information as a String but the data in the snapshot is actually an ArrayList. That is why Firebase throws a DatabaseException.