如何在viewpager中正确实现片段中的工具栏？

// MainActivity.java
public class MainActivity extends AppCompatActivity {
    private ViewPager viewPager;
    private Toolbar toolbar;

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

        viewPager = findViewById(R.id.viewPager);
        toolbar = findViewById(R.id.toolbar);

        setSupportActionBar(toolbar);

        FragmentPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());
        viewPager.setAdapter(adapter);

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            }

            @Override
            public void onPageSelected(int position) {
                // 根据需要对工具栏进行操作
                switch (position) {
                    case 0:
                        toolbar.setTitle("Fragment 1");
                        break;
                    case 1:
                        toolbar.setTitle("Fragment 2");
                        break;
                    case 2:
                        toolbar.setTitle("Fragment 3");
                        break;
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {
            }
        });
    }

    // 自定义PagerAdapter
    private class MyPagerAdapter extends FragmentPagerAdapter {
        private List<Fragment> fragments;

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
            fragments = new ArrayList<>();
            fragments.add(new Fragment1());
            fragments.add(new Fragment2());
            fragments.add(new Fragment3());
        }

        @Override
        public Fragment getItem(int position) {
            return fragments.get(position);
        }

        @Override
        public int getCount() {
            return fragments.size();
        }
    }
}

// Fragment1.java
public class Fragment1 extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1, container, false);
        // 添加Fragment1的内容和工具栏操作
        return view;
    }
}

// Fragment2.java
public class Fragment2 extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment2, container, false);
        // 添加Fragment2的内容和工具栏操作
        return view;
    }
}

// Fragment3.java
public class Fragment3 extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment3, container, false);
        // 添加Fragment3的内容和工具栏操作
        return view;
    }
}