如何将变量从活动传递到片段？ 我对流行的解决方案有疑问

Question

I have problem with passing variable to fragment from my activity. I Have written something like this:

THIS IS PIECE OF MY ACTIVITY CLASS, OnCreate() function

        Bundle bundle = new Bundle();
        bundle.putString("key", "value");
        MembersFragment membersFragment = new MembersFragment();
        membersFragment.setArguments(bundle);

THIS IS PIECE OF MY FRAGMENT CLASS

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            uniCode = getArguments().getString("key");
            textView.setText(uniCode);
        }
    }

And when i want to run my application, TextView is not changed, like arguments are nulls. I have tried so many ways to solve this problem and now i have no idea what is wrong. I think it may be problem with differences beetwen onCreate, onCreateView and onViewCreated, but i give up. Please help me

EDIT1:

To comunicate beetwen activity and fragment i am using something like this:

        tab_layout = findViewById(R.id.tab_layout);
        tab_general = findViewById(R.id.tab_general);
        tab_members = findViewById(R.id.tab_members);
        view_pager = findViewById(R.id.view_pager);
        PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager(),tab_layout.getTabCount());
        view_pager.setAdapter(pagerAdapter);
        tab_layout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                view_pager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

EDIT 3:

my activity class

public class SpecificTeamActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    DrawerLayout drawer_layout_st;
    NavigationView navigationView_st;
    Toolbar toolbar2_st;

    TabLayout tab_layout;
    TabItem tab_general;
    TabItem tab_members;
    ViewPager view_pager;
    String uniCode;


    @SuppressLint("SetTextI18n")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_specific_team);

        tab_layout = findViewById(R.id.tab_layout);
        tab_general = findViewById(R.id.tab_general);
        tab_members = findViewById(R.id.tab_members);
        view_pager = findViewById(R.id.view_pager);
        PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager(),tab_layout.getTabCount());
        view_pager.setAdapter(pagerAdapter);
        tab_layout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                view_pager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

        view_pager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                TabLayout.Tab tab = tab_layout.getTabAt(position);
                tab.select();
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        groupTitle = findViewById(R.id.groupTitle);
        uniCode = getIntent().getStringExtra("uniCode");

        groupTitle.setText("Grupa: " + uniCode);


        mDatabase = FirebaseDatabase.getInstance().getReference();
        mAuth = FirebaseAuth.getInstance();
        currentUser = mAuth.getCurrentUser();

        drawer_layout_st = findViewById(R.id.drawer_layout_st);
        navigationView_st = findViewById(R.id.nav_view_st);
        toolbar2_st = findViewById(R.id.toolbar2_st);

        navigationView_st.bringToFront();
        setSupportActionBar(toolbar2_st);
        ActionBarDrawerToggle actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawer_layout_st, toolbar2_st, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer_layout_st.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();
        navigationView_st.setNavigationItemSelectedListener(this);
        navigationView_st.setCheckedItem(R.id.teams);

        Bundle bundle = new Bundle();
        bundle.putString("key", "value");
        MembersFragment membersFragment = new MembersFragment();
        membersFragment.setArguments(bundle);
    }


    @SuppressLint("NonConstantResourceId")
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.teams:
                Intent intent = new Intent(SpecificTeamActivity.this, GroupActivity.class);
                startActivity(intent);
                break;
            case R.id.receipts:
                Intent intent1 = new Intent(SpecificTeamActivity.this, ReceiptActivity.class);
                startActivity(intent1);
                break;
            case R.id.warranty:
                Intent intent2 = new Intent(SpecificTeamActivity.this, WarrantyActivity.class);
                startActivity(intent2);
                break;
            case R.id.stats:
                Intent intent3 = new Intent(SpecificTeamActivity.this, StatsActivity.class);
                startActivity(intent3);
                break;
            case R.id.purch_list:
                Intent intent4 = new Intent(SpecificTeamActivity.this, ShoppingListActivity.class);
                startActivity(intent4);
                break;
            case R.id.logout:
                break;
        }
        drawer_layout_st.closeDrawer(GravityCompat.START);
        return true;
    }

    public String getUniCode(){
        return uniCode;
    }
}

my fragment class code

public class MembersFragment extends Fragment {

    private DatabaseReference mDatabase;
    private FirebaseUser currentUser;
    private FirebaseAuth mAuth;
    private final List<String> membersList = new ArrayList<>();
    private SpecificTeamActivity specificTeamActivity;

    TextView textView;

    ListView listView;

    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String uniCode;

    public MembersFragment() {
        // Required empty public constructor
    }

    public static MembersFragment newInstance(String param1, String param2) {
        MembersFragment fragment = new MembersFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        textView = getView().findViewById(R.id.text_view_test);
        textView.setText("test");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            uniCode = getArguments().getString("key");
            textView.setText(uniCode);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
 

        return inflater.inflate(R.layout.fragment_members, container, false);

    }
}

my adapter class

package com.example.ourmoney;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;

public class PagerAdapter extends FragmentPagerAdapter {

    private int numOfTabs;
    private int selected;

    public PagerAdapter(FragmentManager fm, int numOfTabs) {
        super(fm,numOfTabs);
        this.numOfTabs = numOfTabs;
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {

        switch(position){
            case 0:
                selected = 0;
                return new GeneralFragment();
            case 1:
                selected = 1;
                return new MembersFragment();
            default:
                return null;
        }
    }

    @Override
    public int getCount() {
        return numOfTabs;
    }

    public int getSelected(){
        return selected;
    }
}

Answer 1

1. In your activity, you're not actually doing anything to display the fragment you instantiated. Add a fragment transaction to display your fragment. Also make sure the argument bundle key names are actually aligned.

2. In your fragment, you're trying to set the textView in onCreate() but you only init it in onViewCreated() . That would crash with an NPE. Move the argument reading and textView setting to onViewCreated() too.