java - 我无法使用 fragment 从我的 Activity 访问 fragment 布局内的 TextView

Question

我已经尝试了以下线程中提到的所有方法 How to access Fragment's child views inside fragment's parent Activity?但它们似乎都不适合我。经过一个半小时的努力，我才提出这个问题。

我的类别 fragment

    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;
        }

         .

         .

         .

 }

当用户单击包含类别选项卡的底部导航 View 时，我将打开类别 fragment 。

我的主屏幕 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;
}

这会引发空指针异常，因为它无法获取 TextView 。任何帮助/指导将不胜感激:)

Answer 1

commit()函数不会同步工作，因此您的 fragment 在调用它之后不会立即准备好。

取自文档。

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.

使用commitNow()，因为它同步工作，并且 fragment 完全进入其主机的 lifycycle 状态。

参见https://developer.android.com/reference/android/support/v4/app/FragmentTransaction.html#commitnow欲了解更多信息