Why doesn't alarmanager start?

Question

Android

Hello, I do everything as in the lessons, I don’t know, maybe the evening is already somewhere stupid. Why is the inscription not displayed?
I'm trying to make an alarm clock, I simplified the code so that everything you need is here

public class MainActivity extends AppCompatActivity {
    private AlarmManager alarmManager;

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

        alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

        Button btn_on = findViewById(R.id.btn_on);
        btn_on.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                makeAlarm();
            }
        });
    }

    private void makeAlarm() {
        Intent intent = new Intent(MainActivity.this, AlarmReceiver.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(getApplicationContext(), 0, intent, 0);
        alarmManager.set(AlarmManager.RTC_WAKEUP, 1000, pendingIntent);
    }
}

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "YEAH BITCH!!!", Toast.LENGTH_LONG).show();
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <Button
        android:id="@+id/btn_on"
        android:text="Запустить"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.danilochagov.alarm">
    <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"
        tools:ignore="GoogleAppIndexingWarning">
        <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=".AlarmReceiver" />
    </application>
</manifest>

Hope you can help me.

Answer 1

For different versions, you need to network the time for the AlarmManager differently.

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            final AlarmManager.AlarmClockInfo alarmClockInfo = new AlarmManager.AlarmClockInfo(triggerTime, pendingIntent);
            alarmManager.setAlarmClock(alarmClockInfo, pendingIntent);
        }
        else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            alarmManager.setExact(AlarmManager.RTC_WAKEUP, triggerTime, pendingIntent);
        } else {
            alarmManager.set(AlarmManager.RTC_WAKEUP, triggerTime, pendingIntent);
        }