03-20 12:34:42.059 1109-1109/? I/xuelb: Recents removeAllTasks task:Task (8962): myapp [com.android.systemui.recents.model.Task@8fc8caf], packageName:myapp, isLocked:false
03-20 12:34:42.137 975-2771/? I/ActivityManager: Killing 29358:myapp/u0a97 (adj 9): remove task
03-20 12:34:42.253 975-1604/? I/WindowState: WIN DEATH: Window{ed062c1 u0 myapp/myapp.MainActivity}
03-20 12:34:42.279 975-1676/? I/ActivityManager: Force stopping myapp appid=10097 user=0: from pid 1109
03-20 12:34:42.279 975-1676/? D/ActivityManager: SVC-handleAppDiedLocked: app = ProcessRecord{1c80011 29358:myapp/u0a97}, app.pid = 29358
03-20 12:34:42.283 975-1676/? V/ActivityManager: Broadcast: Intent { act=android.intent.action.PACKAGE_RESTARTED dat=package:myapp flg=0x10 (has extras) } ordered=false userid=0 callerApp=null
03-20 12:34:42.290 975-986/? W/ActivityManager: Spurious death for ProcessRecord{1c80011 0:myapp/u0a97}, curProc for 29358: null

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button btnStart;
    Button btnGet;

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

        btnStart = (Button) findViewById(R.id.btn_start);
        btnStart.setOnClickListener(this);
        btnGet = (Button) findViewById(R.id.btn_get);
        btnGet.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v == btnStart) {
            System.out.println("start");
            Intent intent = new Intent(
                    this, MyReceiver.class
            );
            PendingIntent pi = PendingIntent.getBroadcast(this, 1, intent, PendingIntent.FLAG_UPDATE_CURRENT);
            AlarmManager am = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
            am.setAndAllowWhileIdle(AlarmManager.RTC_WAKEUP,
                    System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(30), pi);
        }
        if (v == btnGet) {
            System.out.println("get");
            SharedPreferences demo = getSharedPreferences("demo", MODE_PRIVATE);
            String time = demo.getString("time", "?");
            setTitle(time + " " + new Date().getTime());

        }

    }

}

public class MyReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("demo");
        SharedPreferences p = context.getSharedPreferences("demo", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = p.edit();
        editor.putString("time", new Date().getTime()+"");
        editor.commit();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent"
    tools:context="com.example.dmitres.myapplication.MainActivity">

    <Button
        android:id="@+id/btn_start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="start"/>

    <Button
        android:id="@+id/btn_get"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="get"/>

</LinearLayout>

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

    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        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>

        <receiver
            android:name=".MyReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED"/>
            </intent-filter>
        </receiver>

    </application>

</manifest>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.dmitres.myapplication">
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        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>
        <receiver
            android:name=".MainReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED"/>
            </intent-filter>
        </receiver>
        <receiver
            android:name=".NotifReceiver"
            android:enabled="true"
            android:exported="true" />
        <service
            android:name=".AlarmService"
            android:enabled="true"
            android:exported="true"/>
    </application>
</manifest>

public class AlarmService extends Service {
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.println("start command");
        PendingIntent pi = PendingIntent.getBroadcast(getApplicationContext(), 1,
                new Intent(getApplicationContext(), NotifReceiver.class), PendingIntent.FLAG_UPDATE_CURRENT);
        AlarmManager am = (AlarmManager) getApplicationContext().getSystemService(Context.ALARM_SERVICE);
        am.setAndAllowWhileIdle(AlarmManager.RTC_WAKEUP,
                System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(30), pi);
        return START_STICKY;
    }
}

public class NotifReceiver extends WakefulBroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("got alarm call!");
        SharedPreferences p = context.getSharedPreferences("demo", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = p.edit();
        editor.putString("time", System.currentTimeMillis() + "");
        editor.commit();
    }
}

public class MainReceiver extends WakefulBroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("main receiver");
        context.startService(new Intent(context, AlarmService.class));
    }
}

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button btnStart;
    Button btnGet;

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

        btnStart = (Button) findViewById(R.id.btn_start);
        btnStart.setOnClickListener(this);
        btnGet = (Button) findViewById(R.id.btn_get);
        btnGet.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v == btnStart) {
            System.out.println("start");
            Intent intent = new Intent(
                    this, MainReceiver.class);
            PendingIntent pi = PendingIntent.getBroadcast(this, 1, intent, PendingIntent.FLAG_UPDATE_CURRENT);
            try {
                pi.send();
            } catch (PendingIntent.CanceledException e) {
                e.printStackTrace();
            }
        }
        if (v == btnGet) {
            System.out.println("get");
            SharedPreferences demo = getSharedPreferences("demo", MODE_PRIVATE);
            String time = demo.getString("time", "?");
            setTitle(time + " " + new Date().getTime());

        }


    }


}