android - Notifications don't work after -

i learn writing android apps , want make simple application, give user daily notification.

i create app, works when set time of notification few minutes after installing app on phone or don't disconnect phone computer.

for example - yesterday @ 22:30 set alarm on 7:30 today , didn't work, (at 7:40) connect phone computer, install app again, set alarm on 8 , works, set alarm on 21:30 , didn't work again.

any tips or something? think tried know :/

here's code:

public class mainactivity extends appcompatactivity {  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      imagebutton notificationbutton = (imagebutton) findviewbyid(r.id.nofication_button);      notificationbutton.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view view) {             calendar calendar = calendar.getinstance();             calendar.settimeinmillis(system.currenttimemillis());             int curhr = calendar.get(calendar.hour_of_day);             if (curhr > 21)             {                 // since current hour on 21, setting date next day                 calendar.add(calendar.date, 1);             }             calendar.set(calendar.hour_of_day, 21);             calendar.set(calendar.minute, 30);             calendar.set(calendar.second, 12);              intent intent = new intent(getapplicationcontext(), notificationreceiver.class);             pendingintent pendingintent = pendingintent.getbroadcast(getapplicationcontext(), 0, intent, pendingintent.flag_update_current);              alarmmanager alarmmanager = (alarmmanager) getsystemservice(alarm_service);             alarmmanager.setrepeating(alarmmanager.rtc_wakeup, calendar.gettimeinmillis(), alarmmanager.interval_day, pendingintent);         }     }); } } 

and notificationreceiver class:

public class notificationreceiver extends broadcastreceiver {  @override public void onreceive(context context, intent intent) {     notificationmanager notificationmanager = (notificationmanager) context.getsystemservice(context.notification_service);      intent intent1 = new intent(context, mainactivity.class);     intent1.setflags(intent.flag_activity_clear_top);      uri alarmsound = ringtonemanager.getdefaulturi(ringtonemanager.type_notification);      pendingintent pendingintent = pendingintent.getactivity(context, 0, intent1, pendingintent.flag_update_current);      notificationcompat.builder builder = new notificationcompat.builder(context)             .setsmallicon(r.drawable.index)             .setcontentintent(pendingintent)             .setcontenttext("notification text")             .setcontenttitle("notification title")             .setsound(alarmsound)             .setvibrate(new long[]{1000, 1000, 1000, 1000})             .setautocancel(true);      notificationmanager.notify(0, builder.build()); } }