<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 xmlns:tools="http://schemas.android.com/tools" 
 android:id="@+id/LinearLayout1" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
 android:orientation="horizontal" 
 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" 
 android:background="@drawable/bg" > 
 
 <Chronometer 
  android:id="@+id/chronometer" 
  android:layout_marginTop="8dp" 
  android:layout_marginLeft="5dp" 
  android:layout_width="wrap_content" 
  android:layout_height="wrap_content" /> 
 
 <Button 
  android:id="@+id/restart" 
  android:layout_width="wrap_content" 
  android:layout_height="wrap_content" 
  android:text="重置" 
  android:visibility="gone" /> 
 
</LinearLayout> 

package com.example.chronometerdemo; 
 
import android.os.Bundle; 
import android.os.SystemClock; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.Chronometer; 
import android.widget.Chronometer.OnChronometerTickListener; 
 
public class MainActivity extends Activity 
{ 
 Chronometer time=null; 
 Button restart=null; 
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_main); 
   
  time=(Chronometer) findViewById(R.id.chronometer); 
  restart=(Button) findViewById(R.id.restart); 
   
  //設置起始時間和時間格式，然后開始計時 
  time.setBase(SystemClock.elapsedRealtime()); 
  time.setFormat("已用時間：%s"); 
  time.start(); 
   
  //給計時器添加監聽器，當計時到達15s時，要重置 
  time.setOnChronometerTickListener(new OnChronometerTickListener() { 
    
   @Override 
   public void onChronometerTick(Chronometer arg0) 
   { 
    if(SystemClock.elapsedRealtime()-arg0.getBase()>=15000) 
    { 
     arg0.stop(); 
     restart.setVisibility(View.VISIBLE); 
    } 
     
   } 
  }); 
   
  //給按鈕添加重置的效果 
  restart.setOnClickListener(new OnClickListener() { 
    
   @Override 
   public void onClick(View arg0) 
   { 
    time.setBase(SystemClock.elapsedRealtime()); 
    time.start(); 
    restart.setVisibility(View.GONE); 
     
   } 
  }); 
 } 
 
 
 @Override 
 public boolean onCreateOptionsMenu(Menu menu) { 
  // Inflate the menu; this adds items to the action bar if it is present. 
  getMenuInflater().inflate(R.menu.main, menu); 
  return true; 
 } 
  
}