<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(jiān)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;  }   }