Saving and reading from shared preferences not working

Question

Trying to learn coding android apps via the android training. I wanted to tinker around with saving stuff to the sharedPreferences.

I have an activity which when you press a button runs this code

public void saveMessage(String message){
    //Save message local
    SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPref.edit();
    editor.putString("message",message);
    editor.commit();

}

and another activity that runs this code when displayed.

public String getMessage(){

    SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
    String message = sharedPref.getString("message","default");

    return message;

}

These two methods should save/read some data. I don't really know what i'm doing wrong.

Whole code of the classes:

MainActivity.java

package com.example.myfirstapp;

import ...;


public class MainActivity extends AppCompatActivity {

public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

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

/** Called when the User clicks the Send button */
public void sendMessage(View view) {
    Intent intent = new Intent(this, DisplayMessageActivity.class);
    EditText editText = (EditText) findViewById(R.id.edit_message);
    String message = editText.getText().toString();

    saveMessage(message);

    intent.putExtra(EXTRA_MESSAGE, message);
    startActivity(intent);
}

public void saveMessage(String message){
    //Save message local
    SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPref.edit();
    editor.putString("message",message);
    editor.commit();

}
}

DisplayMessageActivity.java

package com.example.myfirstapp;

import ...;

public class DisplayMessageActivity extends AppCompatActivity {

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

    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
    message = getMessage();

    TextView textView = new TextView(this);
    textView.setTextSize(40);
    textView.setText(message);

    ViewGroup layout = (ViewGroup) findViewById(R.id.activity_display_message);
    layout.addView(textView);
}

public String getMessage(){

    SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
    String message = sharedPref.getString("message","default");

    return message;

}
}

Answer 1

According to android doc:

Activity persistent state is managed with the method getPreferences(int), allowing you to retrieve and modify a set of name/value pairs associated with the activity. To use preferences that are shared across multiple application components (activities, receivers, services, providers), you can use the underlying Context.getSharedPreferences() method to retrieve a preferences object stored under a specific name.

So if you want to share data between separate activity I think you may have to use getSharedPreferences() method.

Sample code to write:

SharedPreferences sharedPref = getSharedPreferences("PREF_NAME", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("message",message);
editor.commit();