title: NullPointerException:Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
body: <p>So,I'm doing 2 fragments in a activity and 1 fragment uses a listview+array adapter.
  but when i try to create a instance of the adapter it is null. 
  i saw olther people with the same problem and what worked for them didn't work for me.
  ALSO THIS IS THE FIRST APP THAT I MADE ON MY OWN SO DON'T GET MAD IF I AM DUMB</p>
  
  <p>MyFragment.onCreateView</p>
  
  <pre><code>@Override
  public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                           Bundle savedInstanceState) {
      View rootView =inflater.inflate(R.layout.fragment_todo, container, false);
      ListView listView = rootView.findViewById(R.id.list_view);
  
  
      ArrayList&lt;Task&gt; arrayList = new ArrayList&lt;&gt;();
      arrayList.add(new Task("this is a placeholder todo",Task.PRIORITY_LOW, new Date()));
      arrayList.add(new Task("this is a placeholder todo",Task.PRIORITY_MEDIUM, new Date()));
      arrayList.add(new Task("this is a placeholder todo",Task.PRIORITY_HIGH, new Date()));
  
  
      listView.setAdapter(new HomeActivity.TaskAdapter(getActivity(), arrayList,rootView));
  
      ViewModel viewModel = ViewModelProviders.of(this).get(ViewModel.class);
      viewModel.getTasks().observe(this, new Observer&lt;List&lt;Task&gt;&gt;() {
          @Override
          public void onChanged(@Nullable List&lt;Task&gt; taskEntries) {
              //TODO SET THE ADAPTER
          }
      });
  
      return rootView;
  }
  </code></pre>
  
  <p>MyMainActivity wich contains the adapter aswell :</p>
  
  <pre><code>public class HomeActivity extends FragmentActivity {
  
  
  static int colorGreen ;
  static int colorOrange;
  static int colorRed;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_home);
  
      colorGreen=HomeActivity.this.getResources().getColor(R.color.colorGreen);
      colorOrange=HomeActivity.this.getResources().getColor(R.color.colorOrange);
      colorRed=HomeActivity.this.getResources().getColor(R.color.colorPrimaryDark);
  
  
      //FAB
      FloatingActionButton fab = findViewById(R.id.fab);
      fab.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                      .setAction("Action", null).show();
          }
      });
  
      initializeAds();
      DataBase Db = DataBase.getInstance(getApplicationContext());
  
     ViewPager vp = findViewById(R.id.view_pager);
      CustomFragmentPageAdapter myAdapter = new CustomFragmentPageAdapter(getSupportFragmentManager(),this);
     vp.setAdapter(myAdapter);
  
    TabLayout mTabLayout = findViewById(R.id.tabLayout_Home);
     mTabLayout.setupWithViewPager(vp);
  
  
  }
  
  
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.menu_home, menu);
      return true;
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.
      int id = item.getItemId();
  
      //noinspection SimplifiableIfStatement
      if (id == R.id.action_settings) {
          return true;
      }
  
      return super.onOptionsItemSelected(item);
  }
  
  
  public static class TaskAdapter extends ArrayAdapter&lt;Task&gt; {
  
      private View rootView;
  
      public TaskAdapter(Activity context, ArrayList&lt;Task&gt; tasks ,View view) {
          super(context, 0, tasks );
          rootView=view;
  
  
      }
  
      @NonNull
      @Override
      public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
          // Check if the existing view is being reused, otherwise inflate the view
  
          if (convertView == null) {
              convertView = rootView;
  
          }
          Task currentTask = getItem(position);
  
          TextView description = convertView.findViewById(R.id.description_todo);
          if (currentTask != null) {
              description.setText(currentTask.getDescription());
          }
  
          TextView date = convertView.findViewById(R.id.date_todo);
          if (currentTask != null) {
              date.setText(currentTask.getUpdatedAt().toString());
          }
  
          ConstraintLayout constraintLayout = convertView.findViewById(R.id.constraint_layout_todo);
          if (currentTask != null) {
              switch (currentTask.getPriority()){
                  case Task.PRIORITY_LOW:constraintLayout.setBackgroundColor(colorGreen);
                  case Task.PRIORITY_MEDIUM:constraintLayout.setBackgroundColor(colorOrange);
                  case Task.PRIORITY_HIGH:constraintLayout.setBackgroundColor(colorRed);
              }
          }
  
          return convertView;
      }
  }
  </code></pre>