1.NotificationMananer的实例化
NotificationManager notificationManager= (NotificationManager)
context.getSystemService(Context.NOTIFICATION_SERVICE);
2.点击通知后的Intent
Intent notificationIntent = new Intent(context,HomeActivity.class);
PendingIntent contentIntent = PendingIntent.getActivity(context, 0, notificationIntent, 0);
3.获取到Builder对象
Notification.Builder builder=new Notification.Builder(context);
builder.setSmallIcon(R.mipmap.ic_launcher);//状态栏中的图标
builder.setLargeIcon(BitmapFactory.decodeResource(context.getResources(), R.mipmap.ic_launcher));//通知栏中的图标
builder.setTicker("状态栏中的内容");
builder.setWhen(System.currentTimeMillis());
builder.setContentTitle("Jchat"); //设置通知栏里的标题
builder.setContentText(msg);//设置通知栏中的内容
builder.setContentIntent(contentIntent);
builder.setAutoCancel(true);//点击后自动消失
4.通过build（）方法获取到Notification对象
api16以前是getNotification（）；
Notification notification=builder.build();
5.展示通知
第一个参数为独立的ID，第二参数Notification对象
notificationManager.notify(R.mipmap.ic_launcher,notification);
