无法从 ViewPager 中的 Fragment 编辑 ActionBar 标题

我有一个Activity它通过一个托管多个片段ViewPager。在活动的onCreate方法我使用以下代码来更改ActionBar title:

    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    if(getSupportActionBar() != null) {
        getSupportActionBar().setTitle(getResources().getString(R.string.custom_title));
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

它工作正常，但我无法立即更改它Fragment变得可见。为了检测它，我已经实现了：

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {

    super.setUserVisibleHint(isVisibleToUser);

    if (isVisibleToUser && getContext() != null) {
            ((MainActivity) getContext()).editActionBarTitle("new title");
    }
}

这是定义editActionBarTitle:

public void editActionBarTitle(String title) {
     if(getSupportActionBar() != null) {
         getSupportActionBar().setTitle(title);
         getSupportActionBar().setDisplayHomeAsUpEnabled(true);
     }
}

我可以看到，一旦片段变得可见，该方法就会被调用，但它对 ActionBar 的标题没有影响。为了正确编辑标题，我缺少什么？

EDIT

我也尝试过实施addOnPageChangeListener in the viewPager，我可以看到该方法onPageSelected被调用但对标题没有影响，这是 MainActivity 的示例：

public class MainActivity extends BaseActivity {   

    private NoScrollViewPager mViewPager;
    private SectionsPagerAdapter mAdapter;

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

        // Toolbar initialization
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        if(getSupportActionBar() != null) {
            getSupportActionBar().setTitle("MainActivity");
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        }

        // ViewPager initialization
        mViewPager = findViewById(R.id.containter);
        setupViewPager();
    }

    private void setupViewPager() {

        mAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        mAdapter.addFragment(new Fragment1(), "Fragment 1");
        mAdapter.addFragment(new Fragment2(), "Fragment 2");
        mAdapter.addFragment(new Fragment3(), "Fragment 3");

        mViewPager.setOffscreenPageLimit(mAdapter.getCount());
        mViewPager.setAdapter(mAdapter);

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

            @Override
            public void onPageSelected(int position) {
                setTitle("fragment " + position);
                if(getSupportActionBar() != null) {
                    getSupportActionBar().setTitle("fragment " + position);
                }
            }

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

    public void setViewPager(int position) { mViewPager.setCurrentItem(position); }
}

这是习俗ViewPager class:

public class NoScrollViewPager extends ViewPager {

    // Disable horizontal scrolling in ViewPager
    private boolean isPagingEnabled = false;

    public NoScrollViewPager(Context context) {
        super(context);
    }

    public NoScrollViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    @SuppressLint("AndroidLintClickableViewAccessibility")
    public boolean onTouchEvent(MotionEvent event) {
        return this.isPagingEnabled && super.onTouchEvent(event);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        return this.isPagingEnabled && super.onInterceptTouchEvent(event);
    }

    public void setPagingEnabled(boolean b) {
        this.isPagingEnabled = b;
    }
}

这是自定义的 Adapter 类：

public class SectionsPagerAdapter extends FragmentStatePagerAdapter {

    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

    private FragmentManager fragmentManager;

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
        fragmentManager = fm;
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }

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

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

    @Override
    public int getItemPosition(Object object) { return POSITION_NONE; }

}

在片段的 onCreateView 方法中尝试这个。也许它会对你有所帮助。

if(getActivity() != null){
     getActivity().setTitle("Your title");
}

如果您在片段中使用了 ViewPager 那么您可以使用

@Override
    public void setUserVisibleHint(boolean isVisible) {
        super.setUserVisibleHint(isVisible);

        if (isVisible) {
            if(getActivity() != null){
               getActivity().setTitle("Your title");
            }
        }
    }