java.lang.IllegalMonitorStateException:对象在notify（）之前未被线程锁定

//我从sq lite数据库的数据处理程序类中获取数据

public class ReminderReciever extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm");
List<Reminder> reminderList;
Date dateobj = new Date();

//我检查了所有其他课程，一切正常。在这里，它显示了一个错误，对象在通知前未锁定线程

   alert.notify();
                 }

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

   NotificationManager notificationManager = (NotificationManager)                                                   context.getSystemService(Context.NOTIFICATION_SERVICE);
  Uri alert = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_ALARM);
  if (alert == null) {
       alert = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_RINGTONE);
                }
   Notification.Builder builder = new Notification.Builder(context);
   NotificationManager manager = (NotificationManager)                    context.getSystemService(context.NOTIFICATION_SERVICE);
 Notification myNotication;
 builder.setSmallIcon(R.drawable.st);
 builder.setContentTitle("SharedTasklist Notification");
builder.setTicker("SharedTasklist Reminder");
builder .setContentText("It's time to do " + taskName);
builder .setAutoCancel(true);
builder .setOngoing(true);
builder .setContentIntent(pendingIntent);
builder .setSound(alert); //This sets the sound to play
builder.build();
builder.getNotification().flags |= Notification.FLAG_AUTO_CANCEL;
myNotication = builder.getNotification();
Random random = new Random();
int m = random.nextInt(9999 - 1000) + 1000;
manager.notify(m, myNotication);

   alert.notify();
                 }

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}