So I am trying to switch to another fragment by clicking one of the tabs in my BottomNavigationView but I keep getting NullPointer Exception.
I tried changing the fragment tag in my xml file to androidx.fragment.app.FragmentContainerView but I still get the same error.
Logcat:
java.lang.NullPointerException: Attempt to read from field 'androidx.fragment.app.FragmentManager androidx.fragment.app.Fragment.mFragmentManager' on a null object reference
at androidx.fragment.app.BackStackRecord.hide(BackStackRecord.java:201)
at com.murkoff.MusicPlayer.MainActivity$1.onNavigationItemChanged(MainActivity.java:214)
at com.volcaniccoder.bottomify.BottomifyNavigationView.selectItem(BottomifyNavigationView.kt:240)
at com.volcaniccoder.bottomify.BottomifyNavigationView.access$selectItem(BottomifyNavigationView.kt:19)
at com.volcaniccoder.bottomify.BottomifyNavigationView$addListener$1.onTouch(BottomifyNavigationView.kt:207)
at android.view.View.dispatchTouchEvent(View.java:11830)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2994)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2659)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3000)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2673)
at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:592)
at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1977)
at android.app.Activity.dispatchTouchEvent(Activity.java:3405)
at androidx.appcompat.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:69)
at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:548)
at android.view.View.dispatchPointerEvent(View.java:12095)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4966)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4761)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4259)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4329)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4287)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4429)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4295)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4486)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4259)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4329)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4287)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4295)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4259)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6854)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6828)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6783)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6966)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:194)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:329)
at android.os.Looper.loop(Looper.java:150)
2021-03-06 01:12:37.661 27094-27094/com.murkoff.MusicPlayer E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6702)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:826)
xml for the activity:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.motion.widget.MotionLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/black"
android:id="@+id/activity_main_motionlayout_test_container"
tools:context=".MainActivity" app:layoutDescription="@xml/activity_main_motionlayout_test_scene">
<androidx.constraintlayout.widget.ConstraintLayout android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintBottom_toTopOf="@+id/main_bottom_nav_bar"
android:id="@+id/main_activity_fragment_container"
app:layout_constraintTop_toTopOf="parent">
<androidx.fragment.app.FragmentContainerView
android:layout_width="0dp"
android:layout_height="0dp" android:name="com.murkoff.MusicPlayer.HomeFragment"
android:id="@+id/fragment_tag" tools:layout="@layout/fragment_home"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintTop_toTopOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
<com.volcaniccoder.bottomify.BottomifyNavigationView android:layout_width="match_parent"
android:layout_height="60dp"
android:id="@+id/main_bottom_nav_bar"
android:background="#0E0E0E"
android:elevation="8dp"
app:menu="@menu/main_menu_bottom_bar"
app:item_text_size="13sp"
app:active_color="@color/bottomifyActiveColor"
app:passive_color="@color/bottomifyPassiveColor"
app:pressed_color="@color/bottomifyPressedColor"
android:orientation="horizontal"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:gravity="center_vertical"/>
</androidx.constraintlayout.motion.widget.MotionLayout>
Activity:
I am using fragment1, fragment2, fragment3, fragment4 variables to prevent recreation of fragment as shown in BottomNavigationView - How to avoid recreation of Fragments and reuse them
public class MainActivity extends AppCompatActivity{
BottomifyNavigationView navigationView;
HomeFragment fragment1;
SearchFragment fragment2;
PlaylistsFragment fragment3;
SettingsFragment fragment4;
final FragmentManager fragmentManager = getSupportFragmentManager();
Fragment active = fragment1;
boolean added = false;
FragmentManager mFragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_motionlayout);
if(fragmentManager!=null) {
mFragmentManager = fragmentManager;
Log.d("main activity", "fragment manager not null");
}
navigationView = findViewById(R.id.main_bottom_nav_bar);
fragment1 = new HomeFragment();
fragment2 = new SearchFragment();
fragment3 = new PlaylistsFragment();
fragment4 = new SettingsFragment();
}
@Override
protected void onStart() {
super.onStart();
if(!added) {
fragmentManager.beginTransaction().add(R.id.main_activity_fragment_container_motionlayout, fragment4, "4").hide(fragment4).commit();
fragmentManager.beginTransaction().add(R.id.main_activity_fragment_container_motionlayout, fragment3, "3").hide(fragment3).commit();
fragmentManager.beginTransaction().add(R.id.main_activity_fragment_container_motionlayout, fragment2, "2").hide(fragment2).commit();
fragmentManager.beginTransaction().add(R.id.main_activity_fragment_container_motionlayout, fragment1, "1").commit();
added = true;
}
navigationView.setOnNavigationItemChangedListener(new OnNavigationItemChangeListener() {
@Override
public void onNavigationItemChanged(@NonNull BottomifyNavigationView.NavigationItem navigationItem) {
switch(navigationItem.getPosition()){
case 0:
mFragmentManager.beginTransaction().hide(active).show(fragment1).commit();
active = fragment1;
break;
case 1:
Log.d("fragment", "commiting");
mFragmentManager.beginTransaction().hide(active).show(fragment2).commit();
active = fragment2;
break;
case 2:
mFragmentManager.beginTransaction().hide(active).show(fragment3).commit();
active = fragment3;
break;
case 3:
mFragmentManager.beginTransaction().hide(active).show(fragment4).commit();
active = fragment4;
break;
}
}
});
}
}
How do I fix this? Thanks for the help!
You cannot call final FragmentManager fragmentManager = getSupportFragmentManager(); during class initialization, because fragment manager in superclass has not been initialized yet. Remove all your class members and replace all mFragmentManager and fragmentManager with getSupportFragmentManager()