钟表---定时计时时间

java文件

package com.luck.clock;

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 Clock extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_clock);
final Chronometer ch=(Chronometer)findViewById(R.id.ceshi);
Button start=(Button)findViewById(R.id.start);
start.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
//设置开始时间 获得系统实时时间
ch.setBase(SystemClock.elapsedRealtime());
// 开始计时
ch.start();
}
});
ch.setOnChronometerTickListener(new OnChronometerTickListener() {

@Override
public void onChronometerTick(Chronometer arg0) {
// 20s后停止计时
if(SystemClock.elapsedRealtime()-ch.getBase()>20*1000){
ch.stop();
}
}
});
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.clock, menu);
return true;
}

}

布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_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=".Clock" >

<Chronometer
android:id="@+id/ceshi"
android:layout_width="100dp"
android:layout_height="50dp"
android:text="@string/ceshi"
/>
<Button android:id="@+id/start"
android:layout_width="100dp"
android:layout_height="50dp"
android:text="@string/start"
android:textColor="#000000"
android:layout_below="@id/ceshi"
/>
<AnalogClock
android:id="@+id/ac"
android:layout_below="@id/start"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>

<DigitalClock
android:layout_below="@id/ac"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="14pt"
/>
</RelativeLayout>