android实现倒计时功能的方法

<?xml version="1.0" encoding="utf-8"?>
<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">

 <TextView
  android:id="@+id/count_down"
  android:layout_width="60dp"
  android:layout_height="60dp"
  android:layout_alignParentRight="true"
  android:layout_alignParentTop="true"
  android:layout_marginRight="16dp"
  android:layout_marginTop="16dp"
  android:gravity="center"
  android:textSize="32sp"
  android:textColor="#50000000"
  android:background="@drawable/count_down_background"
  tools:text="2"
  />
</RelativeLayout>

package com.example.counttimer;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.Menu;
import android.view.MenuItem;
import android.view.Window;
import android.widget.TextView;

public class WelcomeActivity extends Activity {
 private final static int COUNT = 1;
 private TextView countDown;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 requestWindowFeature(Window.FEATURE_NO_TITLE);
 setContentView(R.layout.activity_welcome);
 initView();
 }
 //sehedule的第而个参数是第一次启动延时的时间，第三个是每隔多长时间执行一次。单位都是ms。　　//因此这里是每一秒发送一次消息给handler更新UI。　　//然后三秒后时间到了，在timer的第二个sehedule中进行跳转到另外一个界面
 private void initView() {
 countDown = (TextView) findViewById(R.id.count_down);
 final Timer timer = new Timer();
 final long end = System.currentTimeMillis() + 1000*3;
 timer.schedule(new TimerTask() {
  @Override
  public void run() {
  handler.sendEmptyMessage(COUNT);
  
  }
 }, 0, 1000);
 //这里的schedule的第二个参数意义是到了这个时间尽快运行run里面的方法
 timer.schedule(new TimerTask() {
  
  @Override
  public void run() {
   Intent i = new Intent(WelcomeActivity.this, SecondActivity.class);
   i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
   startActivity(i);
   finish();
   timer.cancel();
  }
 }, new Date(end));
 
 }
 
 private Handler handler = new Handler(){
 int num = 2;
 public void handleMessage(android.os.Message msg) {
  
  switch (msg.what) {
  case COUNT:
  countDown.setText(String.valueOf(num));
  num--;
  break;

  default:
  break;
  }
 };
 };
 
} 

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
 android:shape="rectangle">
 <corners
 android:radius="8dp"/>

 <solid
 android:color="#1e000000"/>
</shape>

package com.example.counttimer;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.view.Window;
import android.widget.TextView;

public class WelcomeActivity extends Activity {
 private final static int COUNT = 1;
 private TextView countDown;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 requestWindowFeature(Window.FEATURE_NO_TITLE);
 setContentView(R.layout.activity_welcome);
 initView();
 }

 private void initView() {
 countDown = (TextView) findViewById(R.id.count_down);　　　　//CountDownTimer构造器的两个参数分别是第一个参数表示总时间，第二个参数表示间隔时间。　　　　//意思就是每隔xxx会回调一次方法onTick，然后xxx之后会回调onFinish方法。
 CountDownTimer timer = new CountDownTimer(3200,1000) {
  int num = 2;
  @Override
  public void onTick(long millisUntilFinished) {
  countDown.setText(String.valueOf(num));
  num--;
  }
  
  @Override
  public void onFinish() {　　　　　　　　　　//计时完成调用
   Intent i = new Intent(WelcomeActivity.this, SecondActivity.class);
   i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
   startActivity(i);
   finish();
  }
 };
 timer.start();
 }
 
}