How to display data from an activity to another and in the same time to save it?

Question

I Want to save a message on a textView, not just to display it in another activity. For example if the application is closed the next time when will be open I want to see the message which I added.

I have two activities.

1. Activity one -> I save the date using SharedPraferences in the variable NAME_RESTAURANT and I sent the date throw method 'getMsg()'

2. Activity two -> I receive the date and I want to put it into a TextView named etWelcomeToRestaurant2

The date is represented by a string which I get it from a EditText named etDRestaurantName in first Activity.

My problem is that in SecondActivity the date is not displayed.

The activity where I save the date and from where I transmite the date to the Other activity

public class AdminAreaActivity extends AppCompatActivity {

        public static final String SHARED_PREFS = "sharedPrefs";
        public static final String RESTAURANT_NAME = "restaurantName";

        private String NAME_RESTAURANT;
        private EditText etDRestaurantName;


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


            etDRestaurantName = findViewById(R.id.etRestaurantName);
            final Button bRestaurantChange = findViewById(R.id.bRestaurantChange);

            bRestaurantChange.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if(!etDRestaurantName.getText().toString().matches("")){
                        Intent mainIntent = new Intent(AdminAreaActivity.this,MainActivity.class);
                        saveData();
                        loadData();
                        etDRestaurantName.getText().clear();
                        startActivity(mainIntent);
                    }
                    else
                    {
                        AlertDialog.Builder builder = new AlertDialog.Builder(AdminAreaActivity.this);
                        builder.setMessage("Failed!")
                                .setNegativeButton("Retry", null)
                                .create()
                                .show();
                    }
                }
            });



        }



        public void saveData(){
            SharedPreferences sharedPreferences =getSharedPreferences(SHARED_PREFS,MODE_PRIVATE);
            SharedPreferences.Editor editor = sharedPreferences.edit();

            editor.putString(RESTAURANT_NAME,etDRestaurantName.getText().toString()+"!");
            editor.apply();
            Toast.makeText(this,"Data saved!",Toast.LENGTH_SHORT);

        }

        public void loadData(){
            SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREFS,MODE_PRIVATE);
            NAME_RESTAURANT = sharedPreferences.getString(RESTAURANT_NAME,"Your Restaurant here!");
        }

        public  String getMsg(){
           return NAME_RESTAURANT;

        }



    }

The activity where I want to put data and where I received it:

public class MainActivity extends AppCompatActivity {

    private TextView etWelcomeToRestaurant2;

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

        final TextView etWelcomeToRestaurant = findViewById(R.id.etWelcomeToRestaurant);
        String messg = "Welcome to,\n";
        etWelcomeToRestaurant.setText(messg);

        etWelcomeToRestaurant2 = findViewById(R.id.etWelcomeToRestaurant2);

        AdminAreaActivity admOBj = new AdminAreaActivity();
        etWelcomeToRestaurant2.setText(((AdminAreaActivity)admOBj).getMsg());

    }


}

Answer 1

In Android, you never should be using the new operator with an Activity class.

MainActivity should instead open the same shared preference file and read the value using the same key used in AdminAreaActivity. You already have the preference file name and key as public static variables, so you can reference those variables from MainActivity.

Better yet, create a helper class to manage the preferences. Call it something like PreferenceHelper and it would look something like this:

public class PreferenceHelper {

    public static final String SHARED_PREFS = "sharedPrefs";
    public static final String RESTAURANT_NAME = "restaurantName";

    public static String getResturantName(Context context) {
        return context.getSharedPreferences(SHARED_PREFS, Context.MODE_PRIVATE).getString(RESTAURANT_NAME,"Your Restaurant here!");
    }

    public static void setResturantName(Context, String name) {
        context.getSharedPreferences(SHARED_PREFS, Context.MODE_PRIVATE).edit().putString(RESTAURANT_NAME, name).apply();
    }
}

Now you can call your helper from both classes.

Answer 2

SharedPreferences might be the wrong way for storing data, because "It is using expensive operations which might slow down an app.". Have a look at Room for storing.

To answer your question:

1. Delete the loadData() method and its execution from your AdminAreaActivity, since you want to load the data in your MainActivity. Additionally you called the wrong SharedPreference name (NAME_RESTAURANT).
2. Only write Constants with capital letters
3. You can edit your saveData() and loadData() to reuse it later

See my fix below

AdminAreaActivity

 public class AdminAreaActivity extends AppCompatActivity {
    public static final String SHARED_PREFS = "sharedPrefs";
    public static final String RESTAURANT_NAME = "restaurantName";

    private EditText etDRestaurantName;

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

        etDRestaurantName = findViewById(R.id.etRestaurantName);
        final Button bRestaurantChange = findViewById(R.id.bRestaurantChange);

        bRestaurantChange.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!etDRestaurantName.getText().toString().matches("")) {
                    Intent mainIntent = new Intent(AdminAreaActivity.this, MainActivity.class);
                    saveData(RESTAURANT_NAME, etDRestaurantName.getText().toString() + "!");
                    etDRestaurantName.getText().clear();
                    startActivity(mainIntent);
                } else {
                    AlertDialog.Builder builder = new AlertDialog.Builder(AdminAreaActivity.this);
                    builder.setMessage("Failed!").setNegativeButton("Retry", null).create().show();
                }
            }
        });

    }

    public void saveData(String prefName, String prefValue) {
        SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();

        editor.putString(prefName, prefValue);
        editor.apply();
        Toast.makeText(this, "Data saved!", Toast.LENGTH_SHORT);

    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

    private TextView etWelcomeToRestaurant2;

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

        final TextView etWelcomeToRestaurant = findViewById(R.id.etWelcomeToRestaurant);
        String messg = "Welcome to,\n";
        etWelcomeToRestaurant.setText(messg);

        etWelcomeToRestaurant2 = findViewById(R.id.etWelcomeToRestaurant2);
        etWelcomeToRestaurant2.setText(loadData(AdminAreaActivity.RESTAURANT_NAME, "Your Restaurant here!"));

    }

    public String loadData(String prefName, String defValue){
        SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREFS,MODE_PRIVATE);
        return sharedPreferences.getString(prefName, defValue);
    }
}