SharedPreferences are re-initialized in onCreate(). Howcome does the text persist?

Question

I have one practical question about the time mSharedPreferences is initialized at, which is in the onCreate() method. How come we retrieve the right text when we call mSharedPreferences.getString(...), despite the fact that the variable has been just initialized two lines before that? If you don't know what I mean, take a look at the following Activity class, more specifically, I would just like of anyone to be kind and explain to me how the text persisted in this lifecycle. The code works as desired, however, I expected it not to 🤔.

import android.content.Context;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    private static final String PREFERENCES_FILE = "com.kareemjeiroudi.shared_preferences_app.preferences";
    private static final String KEY_EDITTEXT = "KEY_EDITTEXT";

    private EditText mEditText;
    private SharedPreferences mSharedPreferences;
    private SharedPreferences.Editor mEditor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mEditText = findViewById(R.id.editText);
        mSharedPreferences = getSharedPreferences(PREFERENCES_FILE, Context.MODE_PRIVATE);
        // retrieve the key-value pairs stored in shared preferences
        String editTextString = mSharedPreferences.getString(KEY_EDITTEXT, "");
        mEditText.setText(editTextString);
    }

    @Override
    protected void onPause() {
        mEditor = mSharedPreferences.edit();
        mEditor.putString(KEY_EDITTEXT, mEditText.getText().toString());
        mEditor.apply();
        super.onPause();
    }
}

Answer 1 · 2019-08-01T07:15:56Z

August 1, 2019 7:15am

Hello Kareem Jeiroudi

The key to SharedPreferences retrieving the value despite being initialized 2 lines before is courtesy of the magic which happens at Onpause() method which I will come to shortly. When you initialize the SharedPreference Android automatically creates an XML file stored under DATA/data/ shared_prefs folder. Changes made by the Edior .apply() ** are stored in this XML file. By the way, **MODE_PRIVATE is the default mode, where the created XML file can only be accessed by the calling Application. PREFERENCE_FILE is the name of the preference file you wish to access. If it does not exist, it will be created.

When *onPause() * method is called (e.g. when the user presses the back button to exit the app) the code inside onPause() is triggered and the Editor.apply() saves changes to the XML File described above.

The next time onCreate() is called, mSharedPreferences.getString(KEY_EDITTEXT, ""); easily reads the data from the existing XML File and returns the String.

Please let us know if this clarifies.

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Kareem Jeiroudi

Kareem Jeiroudi

SharedPreferences are re-initialized in onCreate(). Howcome does the text persist?

1 Answer

Tonnie Fanadez

Tonnie Fanadez

Kareem Jeiroudi

Kareem Jeiroudi

Tonnie Fanadez

Tonnie Fanadez