Android Studio; BottomNavigationView = null

Issue

I don't know why BottomNavigationView null. I'm using the Firebase API and I added some code to add data to JSON file. Now after I did that, one of my Activities just stopped working. It wasn't even the Activity I was working on. My navigation equals null and I checked the XML files. The names are the same and debugging doesn't help either, because it shows me that one line of code that sets the BottomNavigationView and gives me a NullPointer.

This is the Navigation that is creating this problem:

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener

    = new BottomNavigationView.OnNavigationItemSelectedListener() 

  {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_to_dos:
                return true;
            case R.id.navigation_categories:
                intent = new Intent(ToDos.this, Categories.class);
                intent.setFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
                startActivity(intent);
                return true;
            case R.id.navigation_account:
                intent = new Intent(ToDos.this, Account.class);
                intent.setFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
                startActivity(intent);
                return true;
        }
        return false;
    }
};

And this is the part where I initialize everything concerning the Navigaion in the onCreate() function:

BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
        navigation.setSelectedItemId(R.id.navigation_to_dos);

I get this error:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: lb335.bbbaden.ch.pendenzenverwaltung, PID: 25288
              java.lang.RuntimeException: Unable to start activity ComponentInfo{lb335.bbbaden.ch.pendenzenverwaltung/lb335.bbbaden.ch.pendenzenverwaltung.ToDos}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.BottomNavigationView.setOnNavigationItemSelectedListener(android.support.design.widget.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3184)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3279)
                  at android.app.ActivityThread.-wrap12(Unknown Source:0)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1881)
                  at android.os.Handler.dispatchMessage(Handler.java:108)
                  at android.os.Looper.loop(Looper.java:166)
                  at android.app.ActivityThread.main(ActivityThread.java:7406)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:926)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.BottomNavigationView.setOnNavigationItemSelectedListener(android.support.design.widget.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference
                  at lb335.bbbaden.ch.pendenzenverwaltung.ToDos.onCreate(ToDos.java:76)
                  at android.app.Activity.performCreate(Activity.java:7365)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3137)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3279) 
                  at android.app.ActivityThread.-wrap12(Unknown Source:0) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1881) 
                  at android.os.Handler.dispatchMessage(Handler.java:108) 
                  at android.os.Looper.loop(Looper.java:166) 
                  at android.app.ActivityThread.main(ActivityThread.java:7406) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:926) 

My Activity XML:

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:background="?android:attr/windowBackground"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:menu="@menu/navigation" />

I'm lost on this one and would really appreciate some help from more experienced Coders.

EDIT:

Thanks to snachmsm I found out, that I had my order of functions was all messed up. I executed findViewById() before I actually set the content. I had to switch that out and now it works.

Solution

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.BottomNavigationView.setOnNavigationItemSelectedListener(android.support.design.widget.BottomNavigationView$OnNavigationItemSelectedListener)' on a null object reference

your BottomNavigationView is null, thats a fact. this line isn't fetching your View:

BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);

are you shure your BottomNavigationView belongs to inflated layout? R.id.navigation is set properly for BottomNavigationView? show some XML and more code from onCreate method. maybe inproper order? (e.g. findViewById called before setContentView)

edit: ok, id is set properly for View inside XML, but you posted only small part of it, show also how do you inflate this XML inside Activity

Answered By - snachmsm