<?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的第而個(gè)參數(shù)是第一次啟動(dòng)延時(shí)的時(shí)間，第三個(gè)是每隔多長時(shí)間執(zhí)行一次。單位都是ms?！　?/因此這里是每一秒發(fā)送一次消息給handler更新UI。　　//然后三秒后時(shí)間到了，在timer的第二個(gè)sehedule中進(jìn)行跳轉(zhuǎn)到另外一個(gè)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); //這里的schedule的第二個(gè)參數(shù)意義是到了這個(gè)時(shí)間盡快運(yùn)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構(gòu)造器的兩個(gè)參數(shù)分別是第一個(gè)參數(shù)表示總時(shí)間，第二個(gè)參數(shù)表示間隔時(shí)間?！　　　?/意思就是每隔xxx會回調(diào)一次方法onTick，然后xxx之后會回調(diào)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() {　　　　　　　　　　//計(jì)時(shí)完成調(diào)用   Intent i = new Intent(WelcomeActivity.this, SecondActivity.class);   i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);   startActivity(i);   finish();  } }; timer.start(); } }