Invisible Activities

AndroidManifest.xml

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

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

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

        <activity
            android:name=".InvisibleActivity"
            android:theme="@style/AppTheme.Transparent" />
    </application>

</manifest>

InvisibleActivity.java

package com.google.firebase.quickstart.invisibleactivitytest;

import android.app.Activity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;

import java.util.Random;

public class InvisibleActivity extends Activity {

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

        new AsyncTask<Void, Void, Integer>() {

            @Override
            protected Integer doInBackground(Void... voids) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                return new Random().nextInt(1000);
            }

            @Override
            protected void onPostExecute(Integer result) {
                Intent data = new Intent();
                data.putExtra("RESULT", result);

                InvisibleActivity.this.setResult(RESULT_OK, data);
                InvisibleActivity.this.finish();
            }
        }.execute();
    }
}

MainActivity.java

package com.google.firebase.quickstart.invisibleactivitytest;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

        startActivityForResult(new Intent(this, InvisibleActivity.class), 1000);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == 1000) {
            int result = data.getIntExtra("RESULT", -1);
            Toast.makeText(this, "RESULT: " + result, Toast.LENGTH_SHORT).show();
        }
    }
}

styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <style name="AppTheme.Transparent" parent="android:Theme">
        <item name="android:windowIsTranslucent">true</item>
        <item name="android:windowBackground">@android:color/transparent</item>
        <item name="android:windowContentOverlay">@null</item>
        <item name="android:windowNoTitle">true</item>
        <item name="android:windowIsFloating">true</item>
        <item name="android:backgroundDimEnabled">false</item>
    </style>

</resources>