Android通知NotificationCompat

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="cn.wuxiaocheng.notification.MainActivity">

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="btn"
android:text="Notification" />
</RelativeLayout>

package cn.wuxiaocheng.notification;

import android.app.Notification;
import android.app.NotificationManager;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

;

public class MainActivity extends AppCompatActivity {
private int counter = 0;
private static final int NOTIFICATION_ID = 1;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}

public void btn(View view) {
counter++;
NotificationCompat.Builder builder = new NotificationCompat.Builder(MainActivity.this);
builder.setSmallIcon(R.mipmap.ic_launcher);
builder.setContentTitle("你有" + counter + "条信息");
builder.setContentText("NotificationCompat内容");
Notification notification = builder.build();
NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
manager.notify(NOTIFICATION_ID, notification);
}
}