Android Notification does not appear in BroadcastReceiver -

i'm trying create notification after amount of seconds entered user. seems me, alarmmanager , broadcastreceiver works fine (the toast in onreceive() appears after correct amount of time) notification not work (it not appear).

so wrong notification?

this code:

mainactivity:

package com.example.user.alarm; import android.app.alarmmanager; import android.app.pendingintent; import android.content.intent; import android.os.bundle; import android.support.v7.app.appcompatactivity; import android.view.view; import android.widget.button; import android.widget.edittext;   public class mainactivity extends appcompatactivity {  button btn_set; edittext et_time;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);       btn_set = (button) findviewbyid(r.id.setalarmbutton);     et_time = (edittext) findviewbyid(r.id.edittext);      btn_set.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view view) {              int time = integer.parseint(et_time.gettext().tostring());              intent intent = new intent(mainactivity.this, alarm.class);             pendingintent pi = pendingintent.getbroadcast(getapplicationcontext(), 0, intent, 0);             alarmmanager = (alarmmanager) getsystemservice(alarm_service);             am.set(alarmmanager.rtc_wakeup, system.currenttimemillis()+time*1000, pi );          }     }); } } 

alarm

package com.example.user.alarm;  import android.app.notificationmanager; import android.content.broadcastreceiver; import android.content.context; import android.content.intent; import android.support.v4.app.notificationcompat; import android.widget.toast;    public class alarm extends broadcastreceiver { @override public void onreceive(context context, intent intent1) {      notificationcompat.builder mbuilder = new notificationcompat.builder(context);     mbuilder.setsmallicon(r.drawable.ic_action_name);     mbuilder.setcontenttitle("notification alert, click me!");     mbuilder.setcontenttext("hi, android notification detail!");      notificationmanager mnotificationmanager = (notificationmanager) context.getsystemservice(context.notification_service);     // notificationid allows update notification later on.     mnotificationmanager.notify(0, mbuilder.build());      toast.maketext(context, "alarm alarm alarm", toast.length_short).show(); } } 

manifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.user.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">       <activity         android:name="com.example.user.alarm.mainactivity"         android:label="@string/app_name">         <intent-filter>             <action android:name="android.intent.action.main" />              <category android:name="android.intent.category.launcher" />         </intent-filter>     </activity>      <receiver android:name="com.example.user.alarm.alarm"         /> </application> 

if target api android o, need channel id.

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