Android编程之简单计时器实现方法

<?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"
>
<Chronometer
android: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=" 开始计时 " />
  <item android:id="@+id/timer_stop" android:title=" 终止计时 " />
  <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);
    // 获得计时器对象
    timer = (Chronometer)this.findViewById(R.id.chronometer);
    //长按计时器时，出现上下文菜单
    this.registerForContextMenu(timer);
  }
  //创建上下文菜单
  @Override
  public void onCreateContextMenu(ContextMenu menu, View v,
      ContextMenuInfo menuInfo)
  {
    super.onCreateContextMenu(menu, v, menuInfo);
    // ContextMenu的Item不支持Icon，所以不用再资源文件中，为它们设定图标
    if (v.getId() == R.id.chronometer)
    {
      //加载xml菜单布局文件
      this.getMenuInflater().inflate(R.menu.context_menu, menu);
      // 设定头部图标
      menu.setHeaderIcon(R.drawable.icon);
      // 设定头部标题
      menu.setHeaderTitle(" 计时器控制选项 ");
    }
  }
  //选择菜单项后的响应
  @Override
  public boolean onContextItemSelected(MenuItem item)
  {
    switch (item.getItemId())
    {
    case R.id.timer_start:
      // 将计时器清零
      timer.setBase(SystemClock.elapsedRealtime());
      //开始计时
      timer.start();
      break;
    case R.id.timer_stop:
      //停止计时
      timer.stop();
      break;
    case R.id.timer_reset:
      //将计时器清零
      timer.setBase(SystemClock.elapsedRealtime());
      break;
    }
    return super.onContextItemSelected(item);
  }
}