我有一个问题。 我正在制作一个应用程序，其中一个Activity上有几个片段。 App's home fragment 我正在使用具有三个元素的底部导航。 在其中一个元素中，我已从一个片段转移到另一个片段。 from HomeFragment to MagnetListFragment 当我从该片段转到BasketFragment（底部导航的第三元素）并按返回按钮时，它将使我返回到上一个片段MagnetListFragment，而不是退出应用程序。
如果我直接从主页片段转到BasketFragment或ProfileFragment，则后退按钮会正常工作。从应用程序退出。
我试图为覆盖onBackPress方法创建新的类和接口，但是它不起作用。 我将popbackstack方法放入MagnetListFragment中，但是它也不起作用。在那之后，它甚至没有进入那个班级。
这是我的MainActivity
public class MainActivity extends AppCompatActivity implements MagnetListFragment.OnListFragmentInteractionListener {
private Toolbar toolbar;
// index to identify current nav menu item
public static int navItemIndex = 0;
// Tags to attach fragments
private static final String TAG_HOME = "home";
private static final String TAG_HOME_FRAGMENT = "home_fragment";
public static String CURRENT_TAG = TAG_HOME;
private static final String TAG_FRAGMENT_OTHER = "other_fragment";
private Handler mHandler;
public static BottomNavigationView bottomNavigationView;
CoordinatorLayout coordinatorLayout;
Fragment fragment;
@Override
public void onListFragmentInteraction(MagnetItem item) {
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = findViewById (R.id.toolbar);
setSupportActionBar(toolbar);
mHandler = new Handler();
setUpNavigationView();
coordinatorLayout = findViewById(R.id.coordinator_layout);
bottomNavigationView = findViewById(R.id.bottom_navigation);
CoordinatorLayout.LayoutParams layoutParams = (CoordinatorLayout.LayoutParams) bottomNavigationView.getLayoutParams();
layoutParams.setBehavior(new BottomNavigationBehaviour());
bottomNavigationView.setSelectedItemId(R.id.navigation_home);
fragment = new HomeFragment();
loadFragment(fragment);
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.navigation_home:
fragment = new HomeFragment();
break;
case R.id.navigation_proflie:
fragment = new ProfileFragment();
break;
case R.id.navigation_basket:
fragment = new BasketFragment();
break;
default:
fragment = new HomeFragment();
}
return loadFragment(fragment);
}
});
if (savedInstanceState == null) {
navItemIndex = 0;
CURRENT_TAG = TAG_HOME;
loadHomeFragment();
}
}
public void setUpNavigationView() {
//Setting Navigation View Item Selected Listener to handle the item click of the bottom_navigation menu
getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
if (getSupportFragmentManager().getBackStackEntryCount() > 0 ) {
// getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
onBackPressed();
}
});
} else {
getSupportActionBar().setDisplayHomeAsUpEnabled(false);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
}
});
}
}
});
}
/***
* Returns respected fragment that user
* selected from bottom_navigation menu
*/
private void loadHomeFragment() {
Runnable mPendingRunnable = new Runnable() {
@Override
public void run() {
// this updates image by replacing fragments
// Fragment fragment = getHomeFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager()
.beginTransaction();
fragmentTransaction.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
// fragmentTransaction.replace(R.id.fragment_container, fragment, CURRENT_TAG);
fragmentTransaction.commitAllowingStateLoss();
}
};
// If mPendingRunnable is not null, then add to the message queue
if (mPendingRunnable != null) {
mHandler.post(mPendingRunnable);
}
invalidateOptionsMenu();
}
/* private void setToolbarTitle() {
getSupportActionBar().setTitle(activityTitles[navItemIndex]);
}*/
@Override
public boolean onCreateOptionsMenu(Menu menu) {
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
return super.onOptionsItemSelected(item);
}
private boolean loadFragment(Fragment fragment) {
//switching fragment
if (fragment != null) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment_container, fragment)
.commit();
return true;
}
return false;
}
}
这是我的HomeFragment
public class HomeFragment extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private static final String TAG = "RecyclerViewFragment";
private static final String LAYOUT_MANAGER = "layoutManager";
private static final String TAG_MAGNET_LIST_FRAGMENT = "magnet_list";
private static final String TAG_CALENDAR = "calendar";
private static final String TAG_PROFILE = "profile";
protected RecyclerView mRecyclerView;
protected PrintingAdapter mPrintingAdapter;
protected RecyclerView.LayoutManager mLayoutManager;
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
private Callback<List<Printing>> callback;
public HomeFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment HomeFragment.
*/
// TODO: Rename and change types and number of parameters
public static HomeFragment newInstance(String param1, String param2) {
HomeFragment fragment = new HomeFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
public interface ClickListener {
void onClick(View view, int position);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_home, container, false);
rootView.setTag(TAG);
mRecyclerView = rootView.findViewById(R.id.recycler_view);
mLayoutManager = new LinearLayoutManager(this.getContext());
mPrintingAdapter = new PrintingAdapter();
mRecyclerView.setAdapter(mPrintingAdapter);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setRecycledViewPool(new RecyclerView.RecycledViewPool());
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.addOnItemTouchListener(new RecyclerTouchListener(getActivity().getApplicationContext(), mRecyclerView, new ClickListener() {
@Override
public void onClick(View view, int position) {
Toast.makeText(getActivity().getApplicationContext(), "You just tapped # " + position, Toast.LENGTH_SHORT).show();
switch (position) {
case 0:
Fragment magnetListFragment = new MagnetListFragment();
FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(R.id.fragment_container, magnetListFragment);
transaction.addToBackStack(TAG_MAGNET_LIST_FRAGMENT);
transaction.commit();
break;
case 1:
Fragment calendarFragment = new CalendarFragment();
FragmentTransaction transactionCalendar = getFragmentManager().beginTransaction();
transactionCalendar.replace(R.id.fragment_container, calendarFragment);
transactionCalendar.addToBackStack(TAG_CALENDAR);
transactionCalendar.commit();
break;
}
}
}));
// ArrayList<Printing> printings = new ArrayList<>();
for (int i = 0; i< Data.names.length; i++) {
Printing printing = new Printing(Data.names[i], Data.photosOfMainList[i]);
mPrintingAdapter.addPrinting(printing);
}
return rootView;
}
@Override
public void onResume() {
super.onResume();
((AppCompatActivity) getActivity()).getSupportActionBar().setTitle(R.string.app_name);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
/* if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}*/
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
那是BasketFragment
class BasketFragment : Fragment(), IOnBackPressed {
companion object {
fun newInstance() : BasketFragment {
return BasketFragment()
}
}
private val TAG_BASKET_FRAGMENT = "basket"
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
onBackPressed()
return inflater?.inflate(R.layout.fragment_basket, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val button = activity?.findViewById(R.id.chayra_button) as Button
button.setOnClickListener {
val homeFragment = HomeFragment()
val fragmentManager = activity!!.getSupportFragmentManager()
val transaction = fragmentManager.beginTransaction()
transaction.replace(R.id.fragment_container, homeFragment)
fragmentManager.popBackStack(null, POP_BACK_STACK_INCLUSIVE)
// transaction.addToBackStack(TAG_BASKET_FRAGMENT)
transaction.commit()
bottomNavigationView.setSelectedItemId(R.id.navigation_home)
}
super.onViewCreated(view, savedInstanceState)
}
override fun onResume() {
(activity as AppCompatActivity).supportActionBar!!.setTitle(R.string.app_name)
(activity as AppCompatActivity).supportActionBar!!.setDisplayHomeAsUpEnabled(false)
super.onResume()
}
override fun onBackPressed(): Boolean{
return true
}
}
那就是ProfileFragment
class ProfileFragment : Fragment() {
companion object {
fun newInstance() : ProfileFragment {
return ProfileFragment()
}
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return inflater?.inflate(R.layout.fragment_profile, container, false)
}
override fun onResume() {
(activity as AppCompatActivity).supportActionBar!!.setTitle(R.string.app_name)
(activity as AppCompatActivity).supportActionBar!!.setDisplayHomeAsUpEnabled(false)
super.onResume()
}
}
它是重写BackPressed类，但我认为它已经过时了。
open class BackPressed : AppCompatActivity() {
override fun onBackPressed() {
val homeFragment = HomeFragment()
val fragmentManager = getSupportFragmentManager()
val transaction = fragmentManager.beginTransaction()
transaction.replace(R.id.fragment_container, homeFragment)
fragmentManager.popBackStack("BackPressedClass", FragmentManager.POP_BACK_STACK_INCLUSIVE)
// transaction.addToBackStack(TAG_BASKET_FRAGMENT)
transaction.commit()
MainActivity.bottomNavigationView.setSelectedItemId(R.id.navigation_home)
super.onBackPressed()
}
// override fun onBackPressed() {
/* val fragment =
this.supportFragmentManager.findFragmentById(R.id.fragment_container)
(fragment as? IOnBackPressed)?.onBackPressed()?.not()?.let {
val fragmentManager = supportFragmentManager
fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE)
super.onBackPressed()
}*/
}
及其接口
interface IOnBackPressed{
fun onBackPressed(): Boolean
}