android-计时器

package zhang.Chronometer;
import android.app.Activity;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Chronometer;
public class chronometer extends Activity {
private Chronometer mChronometer;
/* (non-Javadoc)
  * @see android.app.Activity#onCreate(android.os.Bundle)
  */
@Override
protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  Button button;
        mChronometer = (Chronometer) findViewById(R.id.chronometer);
        // Watch for button clicks.
        button = (Button) findViewById(R.id.start);
        button.setOnClickListener(mStartListener);
        button = (Button) findViewById(R.id.stop);
        button.setOnClickListener(mStopListener);
        button = (Button) findViewById(R.id.reset);
        button.setOnClickListener(mResetListener);
    }
View.OnClickListener mStartListener = new OnClickListener() {
    public void onClick(View v) {
        mChronometer.start();
    }
};
View.OnClickListener mStopListener = new OnClickListener() {
    public void onClick(View v) {
        mChronometer.stop();
    }
};
View.OnClickListener mResetListener = new OnClickListener() {
    public void onClick(View v) {
        mChronometer.setBase(SystemClock.elapsedRealtime());
    }
};
View.OnClickListener mSetFormatListener = new OnClickListener() {
    public void onClick(View v) {
        mChronometer.setFormat("Formatted time (%s)");
    }
};
View.OnClickListener mClearFormatListener = new OnClickListener() {
    public void onClick(View v) {
        mChronometer.setFormat(null);
    }
};
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:padding="4dip"
    android:gravity="center_horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <Chronometer android:id="@+id/chronometer"
        android:format="Initial format: "
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0"
        android:paddingBottom="30dip"
        android:paddingTop="30dip"
        />
    <Button android:id="@+id/start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="开始">
        <requestFocus />
    </Button>
    <Button android:id="@+id/stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="停止">
    </Button>
    <Button android:id="@+id/reset"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="重置">
    </Button>
    <Button android:id="@+id/set_format"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="设置格式">
    </Button>
    <Button android:id="@+id/clear_format"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="清除格式">
    </Button>
</LinearLayout>