Android Notification

<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=".MainActivity" >    <Button        android:id="@+id/btnCancel"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentLeft="true"        android:layout_alignParentTop="true"        android:layout_marginLeft="94dp"        android:layout_marginTop="176dp"        android:text="取消消息"" />    <Button        android:id="@+id/btnSend"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignBottom="@+id/btnCancel"        android:layout_alignLeft="@+id/btnCancel"        android:layout_marginBottom="91dp"        android:text="发送消息" /></RelativeLayout>

package com.example.notificationdemo;import android.os.Bundle;import android.annotation.SuppressLint;import android.app.Activity;import android.app.Notification;import android.app.PendingIntent;import android.app.Notification.Builder;import android.app.NotificationManager;import android.content.Intent;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class MainActivity extends Activity implements OnClickListener{Button btnSend,btnCancel;NotificationManager manager;int Notification_ID=1;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);        btnSend = (Button) findViewById(R.id.btnSend);        btnCancel = (Button) findViewById(R.id.btnCancel);        btnSend.setOnClickListener(this);        btnCancel.setOnClickListener(this);    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {             getMenuInflater().inflate(R.menu.main, menu);        return true;    }public void onClick(View v) {switch (v.getId()) {case R.id.btnSend:Notification.Builder builder = new Notification.Builder(this);builder.setSmallIcon(R.drawable.ic_launcher);builder.setTicker("开会");builder.setContentTitle("下午开会");builder.setContentText("去人民大会堂开会");builder.setDefaults(Notification.DEFAULT_ALL);Intent intent = new Intent(this,MainActivity.class);PendingIntent pendingIntent = PendingIntent.getActivity(this,1, intent, 0);builder.setContentIntent(pendingIntent);Notification notification = builder.build();//4.1版本之后manager.notify(Notification_ID,notification);break;case R.id.btnCancel:manager.cancel(Notification_ID);break;}}    }

将Androidmanifest最低版本改为16