<?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);

        }

    }