我无法使用片段从我的活动中访问片段布局内的文本视图

Question

I have tried all the methods mentioned in the following thread How to access Fragment's child views inside fragment's parent Activity? but none of them seem to work for me. Only after trying hard for an hour and a half, I am asking this question.

My CategoriesFragment

    public class CategoriesFragment extends Fragment {

    private TextView textView;

    @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_categories,container,false);
            textView = view.findViewById(R.id.cat_text);
            Log.i("Tag",textView.getText().toString());
            return view;
        }

        public TextView getTextView(){
            return textView;
        }

         .

         .

         .

 }

I am opening the categories fragment when the user clicks on a bottom navigation view consisting of a categories tab.

My HomeScreen Activity

public class HomeScreen extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener, CategoriesFragment.OnFragmentInteractionListener{

 private BottomNavigationView bottomNavigationView;
 private CategoriesFragment categoriesFragment;
 private FrameLayout bottomFrameLayout;
 private TextView textView;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.home_screen);

        bottomNavigationView = findViewById(R.id.bottom_nav_view);
        bottomFrameLayout = findViewById(R.id.bottom_nav_frame);
        categoriesFragment = new CategoriesFragment();
        bottomNavigationView.setOnNavigationItemSelectedListener(this);
}

@Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        switch (menuItem.getItemId()){
             case R.id.bottom_nav_categories :
                getSupportFragmentManager().beginTransaction().replace(R.id.bottom_nav_frame,categoriesFragment).addToBackStack(null).commit();
                textView = categoriesFragment.getTextView();
                textView.setText("DONE"); 
        }
        return true;
}

This throws a null pointer exception, as it is not being able to get the Text view. Any help/guidance would be much appreciated :)

Answer 1

The commit() function does not work synchronously, so your fragment will not be ready directly after the call to it.

Taken from the documentation.

Schedules a commit of this transaction. The commit does not happen immediately; it will be scheduled as work on the main thread to be done the next time that thread is ready.

Use commitNow() as this works synchronously and the fragment is fully brought to the lifycycle state of their host.

See https://developer.android.com/reference/android/support/v4/app/FragmentTransaction.html#commitnow for further information

Answer 2

当您可以将字符串作为参数传递给fragment的公共方法以更改文本时，为什么要从活动中获取textview和设置文本？