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我试图找出在自动生成的导航抽屉活动中更改片段时如何放置额外的数据。

我创建了一个登录活动，当我单击一个按钮时，它会打开一个新的导航抽屉活动（主活动）并添加额外的用户 ID。我有 4 个片段（家庭、关于、联系和分享）是这个导航抽屉。当 main Activity 打开时，它会自动打开 home 片段。

问题是，当主要活动打开时，我想将从登录活动传递的用户 ID 放在主片段中。我该怎么做？

我的主要活动

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;
    private TextView tv_username_header;
    private TextView tv_email_header;
    private static final String HEADER = "header";


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

        int userId = getIntent().getIntExtra("user_id", 0);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int userId = getIntent().getIntExtra("user_id", 0);
                Intent intent = new Intent(MainActivity.this, AddTrip.class);
                intent.putExtra("user_id", userId);
                startActivity(intent);
            }
        });
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_about, R.id.nav_contact, R.id.nav_share)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

//        if(savedInstanceState == null) {
//            Bundle b = new Bundle();
//            //int user_id = getIntent().getIntExtra("user_id", 0);
//            b.putInt("user_id_app", userId);
//            HomeFragment fragment = new HomeFragment();
//            fragment.setArguments(b);
//            Log.v("argument", fragment.getArguments().toString());
//            getSupportFragmentManager().beginTransaction().replace(R.id.nav_host_fragment, fragment).commit();
//        }

//        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
//            @Override
//            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
//                switch (item.getItemId()){
//                    case R.id.nav_home:
//                        Bundle b = new Bundle();
//                        int user_id = getIntent().getIntExtra("user_id", 0);
//                        Log.v("id", String.valueOf(user_id));
//                        b.putInt("user_id_app", user_id);
//                        HomeFragment fragment = new HomeFragment();
//                        fragment.setArguments(b);
//                        getSupportFragmentManager().beginTransaction().replace(R.id.nav_host_fragment, fragment).commit();
//                        drawer.closeDrawer(GravityCompat.START);
//                        break;
//                }
//                return true;
//            }
//        });

        // SETAM NUMELE SI EMAILUL IN HEADER CU SHARED PREFERENCES

        if(getIntent().hasExtra("user_id")) {
            userId = getIntent().getIntExtra("user_id", 0);
            User user = TripDatabase.getInstance(this).userDao().getById(userId);

            setStringValueInSharedPref(this, "nume", "email", user.getFullName(), user.getEmail());
        }

        View navHeader = navigationView.getHeaderView(0);
        tv_username_header = navHeader.findViewById(R.id.tv_username_header);
        tv_email_header = navHeader.findViewById(R.id.textView_email);

        ArrayList<String> list = getStringValueFromSharedPref(this, "nume", "email");
        tv_username_header.setText(list.get(0));
        tv_email_header.setText(list.get(1));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        if (item.getItemId() == R.id.favorite) {
            Intent intent = new Intent(this, FavouriteTrips.class);
            startActivity(intent);
            return true;
        }
        return false;
    }

    public static void setStringValueInSharedPref(Context context, String key1, String key2, String value1, String value2){
        SharedPreferences sharedPreferences = context.getSharedPreferences(HEADER, Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putString(key1, value1);
        editor.putString(key2, value2);
        editor.apply();
    }

    public static ArrayList<String> getStringValueFromSharedPref(Context context, String key1, String key2){
        ArrayList<String> list = new ArrayList<>();
        SharedPreferences sharedPreferences = context.getSharedPreferences(HEADER, Context.MODE_PRIVATE);
        list.add(sharedPreferences.getString(key1, ""));
        list.add(sharedPreferences.getString(key2, ""));
        return list;
    }

    @Override
    public void onBackPressed() {
        startActivity(new Intent(MainActivity.this, LoginActivity.class));
    }
}

我的家片段

public class HomeFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        TextView tv_fara_trip = view.findViewById(R.id.tv_fara_tripuri);
        RecyclerView rv_trips = view.findViewById(R.id.rv_trips);

        Bundle b = this.getArguments();
//        int user_id = b.getInt("user_id_app", 0);

        if(b == null){
            Toast.makeText(view.getContext(), "null", Toast.LENGTH_LONG).show();
        }

        List<Trip> trips = TripDatabase.getInstance(getContext()).tripDao().getAllTrips();
        Log.v("trips", trips.toString());

        if(trips.size() == 0){
            rv_trips.setVisibility(View.GONE);
        } else {
            tv_fara_trip.setVisibility(View.GONE);
        }


        rv_trips.setLayoutManager(new LinearLayoutManager(this.getContext()));
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(trips, this.getContext());
        rv_trips.setAdapter(adapter);
    }
}

在我调用int user_id = b.getInt("user_id_app", 0); 它的家庭片段中，它因错误而崩溃java.lang.NullPointerException: Attempt to invoke virtual method 'int android.os.Bundle.getInt(java.lang.String, int)' on a null object reference at com.example.androidfundamentalsproject.HomeFragment.onViewCreated(HomeFragment.java:36)

编辑1：

主要活动

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

        int user_id = getIntent().getIntExtra("user_id_app", 0);

        Bundle bundle = new Bundle();
        bundle.putInt("user_id_app", user_id);

        HomeFragment homeFragment = new HomeFragment();
        homeFragment.setArguments(bundle);

        getSupportFragmentManager().beginTransaction().replace(R.id.nav_host_fragment, homeFragment, "HomeFragment").commit();


        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int userId = getIntent().getIntExtra("user_id", 0);
                Intent intent = new Intent(MainActivity.this, AddTrip.class);
                intent.putExtra("user_id", userId);
                startActivity(intent);
            }
        });
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_about, R.id.nav_contact, R.id.nav_share)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

        // SETAM NUMELE SI EMAILUL IN HEADER CU SHARED PREFERENCES

        if(getIntent().hasExtra("user_id_app")) {
            user_id = getIntent().getIntExtra("user_id_app", 0);
            User user = TripDatabase.getInstance(this).userDao().getById(user_id);

            setStringValueInSharedPref(this, "nume", "email", user.getFullName(), user.getEmail());
        }

        View navHeader = navigationView.getHeaderView(0);
        tv_username_header = navHeader.findViewById(R.id.tv_username_header);
        tv_email_header = navHeader.findViewById(R.id.textView_email);

        ArrayList<String> list = getStringValueFromSharedPref(this, "nume", "email");
        tv_username_header.setText(list.get(0));
        tv_email_header.setText(list.get(1));
    }

家庭片段

@Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        TextView tv_fara_trip = view.findViewById(R.id.tv_fara_tripuri);
        RecyclerView rv_trips = view.findViewById(R.id.rv_trips);

        int user_id = 0;
        Bundle bundle = getArguments();
        if(bundle != null) {
            user_id = bundle.getInt("user_id_app", 0);
        } else {
            Toast.makeText(view.getContext(), "Bundle is null", Toast.LENGTH_LONG).show();
        }

        List<Trip> trips = TripDatabase.getInstance(getContext()).tripDao().getAllTrips();
        Log.v("trips", trips.toString());

        if(trips.size() == 0){
            rv_trips.setVisibility(View.GONE);
        } else {
            tv_fara_trip.setVisibility(View.GONE);
        }


        rv_trips.setLayoutManager(new LinearLayoutManager(this.getContext()));
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(trips, this.getContext());
        rv_trips.setAdapter(adapter);
    }

编辑 2

我已经对主要活动进行了更新，我在其中保留了捆绑包，而不是

Bundle bundle = new Bundle();
bundle.putInt("user_id", userId);

HomeFragment homeFragment = new HomeFragment();
homeFragment.setArguments(bundle);

        getSupportFragmentManager().beginTransaction().replace(R.id.nav_host_fragment, homeFragment, "HomeFragment").commit();

我放

Bundle bundle = new Bundle();
bundle.putInt("user_id", userId);
navController.navigate(R.id.nav_home, bundle);

这似乎可行，但是当我将片段更改为“about”然后返回“home”时，捆绑包为空。

4

1 回答 1

0

所以，你需要做什么。首先，当您的用户登录时LoginActivity使用：

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("user_id_app", 200);
startActivity(intent);
finish();

之后，onCreate在MainActivity使用中：

int user_id = getIntent().getIntExtra("user_id_app", 0);

现在您可以将该值发送到HomeFragment这样的位置。由于您HomeFragment是应用程序启动后显示的第一个片段，因此请在上述行MainActivity的onCreate下方使用它：

Bundle bundle = new Bundle();
bundle.putInt("user_id_app", user_id);

HomeFragment homeFragment = new HomeFragment();
homeFragment.setArguments(bundle);

getSupportFragmentManager().beginTransaction().replace(R.id.container, homeFragment, "HomeFragment").commit();

然后在你HomeFragment使用这个onViewCreated：

int user_id = 0;
Bundle bundle = getArguments();
if(bundle != null) {
      user_id = bundle.getInt("user_id_app", 0);
} else {
      Toast.makeText(view.getContext(), "Bundle is null", Toast.LENGTH_LONG).show();
}

编辑：

由于您需要为您可以使用的下一个活动和片段保存该值SharedPreferences，因此像这样使用它。在您的 LoginActivity 中保存如下：

SharedPreferences sharedPreferences = getBaseContext().getSharedPreferences("MY_PREF", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putInt("user_id", user_id);
editor.apply();

然后在每个活动/片段中，您可以使用它来获取值：

SharedPreferences sharedPreferences = getBaseContext().getSharedPreferences("MY_PREF", Context.MODE_PRIVATE);
int user_id = sharedPreferences.getInt("user_id", 0); //where 0 is default value

这样您就可以在每个活动或片段中获取您的 user_id。其他方法是将 user_id from 传递LoginActivity给MainActivitywith ，Intent.putExtra()如下所示：

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("user_id", user_id);
startActivity(intent);
finish();

然后MainActivity像这样在里面创建全局变量：

public static int USER_ID = 0;

然后在里面onCreate写这样的东西：

USER_ID = getIntent().getIntExtra("user_id", 0);

然后从每个活动或片段中，您可以像这样访问这个值：

MainActivity.USER_ID //this will be value of user_id
于 2021-01-29T21:37:00.707 回答