Example of how to change themes at runtime with a smooth animation. In this example, we just switch between a light and a dark theme. The activity animation is defined in the theme and as such will be default on all activities with the set theme. [Demo Video here](http://youtu.be/Ps0phswbHls).

AA Transition App theme between light and dark themes

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;


public class TransitionThemeActivity extends AppCompatActivity implements View.OnClickListener {

  ListView mListView;
  Button mChangeTheme;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    AppSettings settings = AppSettings.getInstance(this);
    setTheme(settings.getBoolean(AppSettings.Key.USE_DARK_THEME) ? R.style.AppThemeDark : R.style.AppThemeLight);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_transition_theme);

    mListView = (ListView) findViewById(R.id.cheese_list);
    mListView.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Cheeses.CHEESES));

    mChangeTheme = (Button) findViewById(R.id.change_theme);
    mChangeTheme.setOnClickListener(this);

  }

  @Override
  public void onClick(View v) {
    AppSettings settings = AppSettings.getInstance(this);
    settings.set(AppSettings.Key.USE_DARK_THEME,
        !settings.getBoolean(AppSettings.Key.USE_DARK_THEME));
    Intent intent = new Intent(this, TransitionThemeActivity.class);
    startActivity(intent);
    finish();

  }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.alimuzaffar.android.scratchpad" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppThemeLight" >
        <activity
            android:name=".TransitionThemeActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

theme.xml

<resources>
    <style name="AppThemeLight" parent="Theme.AppCompat.Light">
        <!-- Customize your theme here. -->
        <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item>
    </style>
    <style name="AppThemeDark" parent="Theme.AppCompat">
        <!-- Customize your theme here. -->
        <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item>
    </style>
    <!-- This will set the fade in animation on all your activities by default -->
    <style name="WindowAnimationTransition">
        <item name="android:windowEnterAnimation">@android:anim/fade_in</item>
        <item name="android:windowExitAnimation">@android:anim/fade_out</item>
    </style>
</resources>

So essentially the only actual transition part is

<style name="WindowAnimationTransition">
    <item name="android:windowEnterAnimation">@android:anim/fade_in</item>
    <item name="android:windowExitAnimation">@android:anim/fade_out</item>
</style>

and referenced in any theme with

<item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item>

The other unrelated small bit of code is just a general theme switcher but off-topic to the gist title

Intent intent = new Intent(this, TransitionThemeActivity.class);
startActivity(intent);
finish();

all the rest is completely offtopic and unrelated such as settings saving/loading, general manifest settings, and mechanics and design of switching themes.

To help cleanup for those interested and to save them from skimming through all the lines of code and files.

How can i save the instance of activity

`public class MainActivity extends ActionBarActivity {

protected SharedPreferences mPrefs;

@OverRide
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mPrefs = PreferenceManager.getDefaultSharedPreferences(this);

	SharedPreferences.Editor prefEditor = mPrefs.edit();
	prefEditor.putBoolean("USE_DARK_THEME", !mPrefs.getBoolean("USE_DARK_THEME",false));
	prefEditor.commit();
	setTheme(mPrefs.getBoolean("USE_DARK_THEME",false) ? R.style.AppThemeDark : R.style.AppThemeLight);
            setContentView(R.layout.activity_main);

}

styles.xml

---

<style name="AppThemeLight" parent="Theme.AppCompat.Light"> @style/WindowAnimationTransition </style>

<style name="AppThemeDark" parent="Theme.AppCompat">
    <!-- Customize your theme here. -->
    <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item>
</style>
<!-- This will set the fade in animation on all your activities by default -->
<style name="WindowAnimationTransition">
    <item name="android:windowEnterAnimation">@android:anim/fade_in</item>
    <item name="android:windowExitAnimation">@android:anim/fade_out</item>
</style> 

`

and to do this with react-native?

Thanks for the gist was helpful to implement fade transition in my existing dark/light mode switcher