如何通过 model 将用户输入从登录传递到主片段

Question

I recently started learning Android development and have trouble passing data.

I started with the navigation drawer template on android studio. I have a login page that requires username & password fields. When entered, the login page redirects to a MainActivity.java. But this MainActivity.java comprises of various fragments - HomeFragment, GalleryFragment and Slideshow (these were default from the template). Along with the fragments there are HomeViewModel, GalleryViewModel and SlideshowViewModel.

Requirements: This username should be stored until the app is closed. I do not need to save any session etc because this app is mainly for testing purposes (to test an API and SDK). I have some confusion on when to use SharedPreferences, Bundle passing, LiveModel etc and how I should be passing it.

I've been able to do the saving of username and displaying it on HomeFragment - but I doubt this is the right approach because I think should be passing it through HomeModel? Any help is appreciated. Thanks!!

Most of the code here is from the template.

Login.java

package com.developer.tmx_android_v6;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import com.developer.tmx_android_v6.ui.home.HomeFragment;
import com.developer.tmx_android_v6.ui.home.HomeViewModel;
import com.google.android.material.textfield.TextInputEditText;

public class Login extends AppCompatActivity {

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

    public void signUpHandler(View target) {
        Intent myintent = new Intent(this, SignUp.class);
        startActivity(myintent);

    }


    public void LoginHandler(View target) {

        Intent myintent = new Intent(this, MainActivity.class);
        Bundle bundle = new Bundle();
        bundle.putString("key1", "GFG :- Main Activity");

////        pass user input
        TextInputEditText username = (TextInputEditText) findViewById(R.id.username);
        TextInputEditText password = (TextInputEditText) findViewById(R.id.password);

        String usernameText = username.getText().toString();
        String passwordText = password.getText().toString();

        bundle.putString("username", usernameText);
        bundle.putString("password", passwordText);

        myintent.putExtras(bundle);
        startActivity(myintent);

    }
}

MainActivity.java

package com.developer.tmx_android_v6;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.Menu;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import com.google.android.material.navigation.NavigationView;

import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
//
//        Bundle bundle = getIntent().getExtras();
//
//        String username = bundle.getString("username", "DefaultUsername");
//        String password = bundle.getString("password", "DefaultPassword");
//        Log.i("print values", "Main Activity: username and pw is: " + username + " " + password);

        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        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_gallery, R.id.nav_slideshow)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);
    }



    @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();
    }
}

HomeFragment.java

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.developer.tmx_android_v6.R;

public class HomeFragment extends Fragment {

    private HomeViewModel homeViewModel;

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

//        works but not sure if I should be passing it directly to fragment
//        String username = getActivity().getIntent().getExtras().getString("username");
//        String password = getActivity().getIntent().getExtras().getString("password");
//
//        Log.i("print values", "Home Fragment Activity: username and pw is: " + username  + " " + password);

        homeViewModel =
                ViewModelProviders.of(this).get(HomeViewModel.class);
        View root = inflater.inflate(R.layout.fragment_home, container, false);

        TextView usernameTextView = (TextView) root.findViewById(R.id.username);
        usernameTextView.setText("Welcome, " + username + "!" );

        final TextView textView = root.findViewById(R.id.text_home);
        homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                textView.setText(s);
            }
        });
        return root;
    }
}

HomeViewModel.java

package com.developer.tmx_android_v6.ui.home;


import android.os.Bundle;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class HomeViewModel extends ViewModel {

    private MutableLiveData<String> mText;

    public HomeViewModel() {

//      how to get data and pass it here?

        mText = new MutableLiveData<>();
//        mText.setValue("Welcome! -HomeViewModel-");

    }


    public LiveData<String> getText() {
        return mText;
    }
}

Answer 1

You can pass the LoginActivity 's username fields to the MainActivity with an IntentExtra and then access the passed fields from any Fragment .

1. Declare a public static field where the username and password can be stored and accessed by the fragments. In your MainActvity declare:

    public static String userNameText;
    public static String passwordText;

2. In the onCreate() of MainActivity fetch the Intent 's Extra :

    Intent intent = getIntent();
    userNameText = intent.getStringExtra("username");
    passwordText = intent.getStringExtra("passoword");

3. Then you can access those fields from any fragment by getting the values from the MainActivity since the fields are public and static . In your HomeFragment 's onCreateView() get the values:

    String userNameText  = MainActivity.userNameText;
    String passwordText = MainActivity.passwordText;

Answer 2

Use SharedPreferences for small data with key value pairs like username or password. Use Bundle to pass data from one activity to another. Use ViewModel to store large data which will survive during screen orientation changes.