java - 如何使用后退堆栈或通过此特定寻呼机适配器获取 getChildFragmentManager() 以便使用后退按钮？

Question

我正在使用 Fragments 来更改应用程序中的场景，并且遇到了当按下手机后退按钮时应用程序关闭的问题。我该如何做到这一点，以便当按下后退按钮时，上一个 fragment 会打开。

我搜索了解决方案，有很多类似使用 getChildFragmentManager 或返回堆栈的解决方案。我只是不知道如何为我的特定状态寻呼机适配器实现它，我按照 YouTube 视频教程进行了操作。

SectionsStatePagerAdapter.java:

public class SectionsStatePagerAdapter extends FragmentStatePagerAdapter {

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

    public SectionsStatePagerAdapter(@NonNull FragmentManager fm, int behavior) {
        super(fm, behavior);
    }

    public SectionsStatePagerAdapter(FragmentManager supportFragmentManager) {
        super(supportFragmentManager);
    }

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



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

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

MainActivity.java:

public class MainActivity extends AppCompatActivity implements MyRecyclerViewAdapter.ItemClickListener {
    public SectionsStatePagerAdapter mSectionsStatePagerAdapter;
    private ViewPager mViewPager;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        //Fragment Stuff:
        mSectionsStatePagerAdapter = new SectionsStatePagerAdapter(getSupportFragmentManager());
        mViewPager = findViewById(R.id.container);

        //SetUpPager:
        setupViewPager(mViewPager);

    }


    private void setupViewPager(ViewPager viewPager){
        SectionsStatePagerAdapter adapter = new SectionsStatePagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new MainPageFragment(),"MainPage"); //0
        adapter.addFragment(new CoffeePageFragment(),"CoffeePage"); //1
        adapter.addFragment(new RegularCoffeeFragment(),"RegularCoffeePage"); //2
        viewPager.setAdapter(adapter);
    }


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

}

CoffeePageFragment.java:

public class CoffeePageFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.content_coffee_page,container,false);
        btnRegularCoffee = view.findViewById(R.id.regular_coffee_button);


        btnRegularCoffee.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ((MainActivity)getActivity()).setViewPager(2);
            }
        });
        return (view);
    }
}

总之，如何做到当按下设备后退按钮时，它会返回到上一个 fragment ？

Answer 1

在 AppCompatActivity 实现的早期版本中，覆盖 Activity 中的 onBackPressed() 就足够了，较新的版本要求实现 OnBackPressedCallback ，如下所示:https://developer.android.com/reference/androidx/activity/OnBackPressedDispatcher.html

public class FormEntryFragment extends Fragment {
     @Override
     public void onAttach(@NonNull Context context) {
         super.onAttach(context);
         OnBackPressedCallback callback = new OnBackPressedCallback(
             true // default to enabled
         ) {
             @Override
             public void handleOnBackPressed() {
                 showAreYouSureDialog();
             }
         };
         requireActivity().getOnBackPressedDispatcher().addCallback(
             this, // LifecycleOwner
             callback);
     }
 }

不过，在 Activity 级别使用 onBackPressed 可能仍然可以。