<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical"android:layout_width= "fill_parent"android:layout_height = "fill_parent"android:gravity = "center_horizontal"><Chronometerandroid:id ="@+id/chronometer"android:layout_width="wrap_content"android:layout_height="wrap_content"android:format="%s"android:textSize="80px"android:textColor="#00FF00"/></LinearLayout >

<?xml version="1.0" encoding="utf-8"?><menu xmlns:android="http://schemas.android.com/apk/res/android">  <item android:id="@+id/timer_start" android:title=" 開始計時 " />  <item android:id="@+id/timer_stop" android:title=" 終止計時 " />  <item android:id="@+id/timer_reset" android:title=" 清零 " /></menu>

public class MainActivity extends Activity {  private Chronometer timer;  @Override  public void onCreate(Bundle savedInstanceState)  {    super.onCreate(savedInstanceState);    setContentView(R.layout.main);    // 獲得計時器對象    timer = (Chronometer)this.findViewById(R.id.chronometer);    //長按計時器時，出現上下文菜單    this.registerForContextMenu(timer);  }  //創建上下文菜單  @Override  public void onCreateContextMenu(ContextMenu menu, View v,      ContextMenuInfo menuInfo)  {    super.onCreateContextMenu(menu, v, menuInfo);    // ContextMenu的Item不支持Icon，所以不用再資源文件中，為它們設定圖標    if (v.getId() == R.id.chronometer)    {      //加載xml菜單布局文件      this.getMenuInflater().inflate(R.menu.context_menu, menu);      // 設定頭部圖標      menu.setHeaderIcon(R.drawable.icon);      // 設定頭部標題      menu.setHeaderTitle(" 計時器控制選項 ");    }  }  //選擇菜單項后的響應  @Override  public boolean onContextItemSelected(MenuItem item)  {    switch (item.getItemId())    {    case R.id.timer_start:      // 將計時器清零      timer.setBase(SystemClock.elapsedRealtime());      //開始計時      timer.start();      break;    case R.id.timer_stop:      //停止計時      timer.stop();      break;    case R.id.timer_reset:      //將計時器清零      timer.setBase(SystemClock.elapsedRealtime());      break;    }    return super.onContextItemSelected(item);  }}