当应用程序进入后台时碎片销毁

如何解决当应用程序进入后台时碎片销毁

我遇到了一个问题，我有一个名为“ MainActivity”的活动，其中包含4个片段。问题是，如果我位于片段2或3或4中，并且该应用程序进入后台，如：

1. 如果我打开底部导航，然后将应用转到后台，则在底部导航关闭后，它将我重定向到第一个片段（默认片段）。

2. 如果我最小化应用程序，然后再次恢复它，请转到第一个片段

3. 如果我的手机进入睡眠状态，然后我又在手机上将我重定向到第一个片段。

我不明白为什么会出现这种现象。请给我建议可能的解决方案。

这是主要的活动代码：

public class ContainerActivity extends AppCompatActivity
    implements BottomNavigationView.OnNavigationItemSelectedListener{

private Fragment fragment;
private BottomNavigationView bottomNavigationView;
private RestaurantListFragment restaurantListFragment;
private String completeAddress,cityName,countryName,latitude,longitude,nickName,addressLabel,locationType,currentLock;

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

    if(getIntent().getExtras() != null){
        latitude = getIntent().getExtras().getString("latitude");
        longitude = getIntent().getExtras().getString("longitude");
        completeAddress = getIntent().getExtras().getString("complete_address");
        cityName = getIntent().getExtras().getString("city_name");
        countryName = getIntent().getExtras().getString("country_name");
        nickName = getIntent().getExtras().getString("nick_name");
        addressLabel = getIntent().getExtras().getString("label");
        locationType = getIntent().getExtras().getString("location_type");
        currentLock = getIntent().getExtras().getString("current_lock");

        Bundle bundle = new Bundle();
        bundle.putString("latitude",latitude);
        bundle.putString("longitude",longitude);
        bundle.putString("complete_address",completeAddress);
        bundle.putString("city_name",cityName);
        bundle.putString("country_name",countryName);
        bundle.putString("nick_name",nickName);
        bundle.putString("label",addressLabel);
        bundle.putString("location_type",locationType);
        bundle.putString("current_lock",currentLock);

        restaurantListFragment.setArguments(bundle);
    }
}

@Override
protected void onResume() {
    super.onResume();
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.fragment_container,restaurantListFragment).addToBackStack(null).commit();
}

private void initView() {
    bottomNavigationView = findViewById(R.id.btoom_navigation_view);
    bottomNavigationView.setOnNavigationItemSelectedListener(this);
    bottomNavigationView.setSelectedItemId(R.id.home);
    restaurantListFragment = new RestaurantListFragment();
}

public void openRestaurantMenuFragment(Bundle bundle) {
    RestaurantMenuFragment restaurantMenuFragment = new RestaurantMenuFragment();
    restaurantMenuFragment.setArguments(bundle);

    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container,restaurantMenuFragment)
            .addToBackStack(null)
            .commit();
}

public void openFoodListOrDetailFrgment() {
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container,new FoodDetailFragment())
            .addToBackStack(null)
            .commit();
}

public void openCart(){
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container,new MyOrderFragment())
            .addToBackStack(null)
            .commit();
}

public void openCompleteItemDetailFragment(){
         bottomNavigationView.setVisibility(View.GONE);
}

public void showBottomNavigation(){
    if(bottomNavigationView.getVisibility() == View.GONE){
        bottomNavigationView.setVisibility(View.VISIBLE);
    }
}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
    switch (item.getItemId()) {
        case R.id.home:
            if ((getSupportFragmentManager().findFragmentById(R.id.fragment_container)) != null && !(fragment instanceof RestaurantListFragment)){
                getSupportFragmentManager().beginTransaction()
                        .replace(R.id.fragment_container,new RestaurantListFragment()).addToBackStack(null).commit();
            }
            break;
        case R.id.explore:


            break;
        case R.id.profile:

            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragment_container,new ProfileFragment())
                    .addToBackStack(null)
                    .commit();
            break;

    }
    return true;
}

@Override
public void onBackPressed() {
    Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);

    if(fragment instanceof RestaurantListFragment){
        getSupportFragmentManager().popBackStack(0,getSupportFragmentManager().POP_BACK_STACK_INCLUSIVE);
    }
    if(fragment instanceof CompleteFoodItemDetailFragment || fragment instanceof GoogleMapFragment){
        if(bottomNavigationView.getVisibility() == View.GONE){
            bottomNavigationView.setVisibility(View.VISIBLE);
        }
    }

    super.onBackPressed();
}

}

解决方法

在您的问题中，您是说我想从后台恢复活动时会打开默认片段（restaurantListFragment）。这是由于

onResume（）方法

@Override
protected void onResume() {
    super.onResume();
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.fragment_container,restaurantListFragment).addToBackStack(null).commit();
}

替换为（片段只有在空着或分离时才会更改）

private fm;
initViews(){
   fm = supportFragmentManager.beginTransaction();
}

    @Override
    protected void onResume() {
        super.onResume();

        if(fm.isEmpty() || restaurantListFragment.isDetached()){
            fm.replace(R.id.fragment_container,restaurantListFragment).addToBackStack(null).commit();
        }
    }

还要替换onCreate中的片段

@Override
    protected void onCreate(Bundle savedInstanceState){
    ...
    //below initViews();
    ...
    fm.replace(R.id.fragment_container,restaurantListFragment).addToBackStack(null).commit();
    }