1. 创建通知管理器
    //getSystemService()在Context类或者ContextWrapper类有，一般通过继承后者来持有
    manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

  2. 创建通知渠道对象并将其注入到通知管理器
    //创建渠道对象并指定id、名称和重要性；id将被通知管理器用来确定通知被哪个渠道对象执行
    NotificationChannel notificationChannel1 = new NotificationChannel(CHANNEL1_ID, CHANNEL1_NAME,NotificationManager.IMPORTANCE_HIGH);
    //设置是否锁屏可视
    notificationChannel1.setLockscreenVisibility(Notification.VISIBILITY_PUBLIC);
    //将渠道对象注入到通知管理器
    manager.createNotificationChannel(notificationChannel1);

  3. 创建通知对象并通过.notify(int id, Notification notify)方法发送通知
    Notification.Builder builder = new Notification.Builder(getApplicationContext(), CHANNEL1_ID)
    .setContentTitle(notifyTitle).setContentText(notifyContent).setSmallIcon(R.mipmap.android_img);
    manager.notify(notifyID,builder.build());

  4. 可以给Builder设置点击之后跳转的Activity和点击之后是否取消通知的显示
    Intent intent = new Intent(getApplicationContext(),NotificationAction.class);
    PendingIntent pendingIntent = PendingIntent.getActivity(getApplicationContext(),0,intent,PendingIntent.FLAG_UPDATE_CURRENT);

       builder.setAutoCancel(true).setContentIntent(pendingIntent);