利用Android实现一个倒计时功能

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 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="yascn.com.timecalc.MainActivity">



 <TextView
  android:textSize="20dp"
  android:layout_centerInParent="true"
  android:id="@+id/tv_remaintime"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:textColor="#000000"
  />
</RelativeLayout>

package yascn.com.timecalc;

import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class MainActivity extends AppCompatActivity {


 TextView tv_remaintime;//倒计时
 private long countdownTime;//倒计时的总时间(单位:毫秒)
 private String timefromServer;//从服务器获取的订单生成时间
 private long chaoshitime;//从服务器获取订单有效时长(单位:毫秒)

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  tv_remaintime = (TextView) findViewById(R.id.tv_remaintime);

  getTimeDuring();

 }


 Handler handler = new Handler();
 Runnable runnable = new Runnable() {
  @Override
  public void run() {
   countdownTime -= 1000;//倒计时总时间减1

   SimpleDateFormat minforamt = new SimpleDateFormat("mm:ss");

   String hms = minforamt.format(countdownTime);//格式化倒计时的总时间
   tv_remaintime.setText("还剩下" + hms);
   handler.postDelayed(this, 1000);
  }
 };


 private void getTimeDuring() {
  chaoshitime = 30 * 60 * 1000;//应该从服务器获取

  timefromServer = "2017-01-23 11:40:50";//应该从服务器获取
  SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  try {
   Date serverDate = df.parse(timefromServer);

   long duringTime = new Date().getTime() - serverDate.getTime();//计算当前时间和从服务器获取的订单生成时间的时间差
   countdownTime = chaoshitime - duringTime;//计算倒计时的总时间

   handler.postDelayed(runnable, 1000);

  } catch (ParseException e) {
   e.printStackTrace();
  }


 }
}