<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main2"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical"
tools:context="com.mly.panhouye.handlerdemo.Main2Activity">
 <TextView
 android:gravity="center"
 android:textSize="30sp"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:text="NO DATA"
 android:id="@+id/tv"/>
</LinearLayout>

public class Main2Activity extends AppCompatActivity {
 TextView tv;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main2);
 tv = (TextView) findViewById(R.id.tv);
 new Thread(new Runnable() {
  @Override
  public void run() {
  for (int i=5;i>0;i--){
   tv.setText(String.valueOf(i));
   try {
   Thread.sleep(1000);
   } catch (InterruptedException e) {
   e.printStackTrace();
   }
  }
  //计时结束后跳转到其他界面
  startActivity(new Intent(Main2Activity.this,Main3Activity.class));
  //添加finish方法在任务栈中销毁倒计时界面，使新开界面在回退时直接退出而不是再次返回该界面
  finish();
  }
 }).start();
 }

package com.mly.panhouye.handlerdemo;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.TextView;
/**
 * Handler:
 * 1 处理的消息对象就是Message,理解为要传递的消息数据的封装对象
 * Message what : 标记,用来区分多个消息
 * Message arg1,arg2 : 用来传递int类型的数据
 * Message obj : 可以传递任何类型的对象(Object)
 */
public class Main2Activity extends AppCompatActivity {
 public static final int UPDATE = 0x1;
 TextView tv;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main2);
 tv = (TextView) findViewById(R.id.tv);
 begin();//开启倒计时并跳转页面的方法
 }
 //消息处理者,创建一个Handler的子类对象,目的是重写Handler的处理消息的方法(handleMessage())
 private Handler handler = new Handler(){
 @Override
 public void handleMessage(Message msg) {
  switch (msg.what){
  case UPDATE:
   tv.setText(String.valueOf(msg.arg1));
   break;
  }
 }
 };
 public void begin(){
 new Thread(new Runnable() {
  @Override
  public void run() {
  for (int i=5;i>0;i--){
   Message msg = new Message();
   msg.what = UPDATE;
   msg.arg1 = i;
   handler.sendMessage(msg);
   try {
   Thread.sleep(1000);//休眠1秒
   } catch (InterruptedException e) {
   e.printStackTrace();
   }
   //打印log
   Log.i("tag",Main2Activity.this+"-"+ i);
  }
  //计时结束后跳转到其他界面
  startActivity(new Intent(Main2Activity.this,Main3Activity.class));
  //添加finish方法在任务栈中销毁倒计时界面，使新开界面在回退时直接退出而不是再次返回该界面
  finish();
  }
 }).start();
 }
 @Override
 protected void onDestroy() {
 super.onDestroy();
 //log打印用于测试activity销毁
 Log.i("tag","destory");
 }
}

package com.mly.panhouye.handlerdemo;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.TextView;
import java.lang.ref.WeakReference;
public class Main4Activity extends AppCompatActivity {
 public static final int UPDATE = 0x1;
 TextView tv;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main2);
 tv = (TextView) findViewById(R.id.tv);
 begin();//开启倒计时并跳转页面的方法
 }
 //Handler静态内部类
 private static class MyHandler extends Handler {
 //弱引用
 WeakReference<Main4Activity> weakReference;
 public MyHandler(Main4Activity activity) {
  weakReference = new WeakReference<Main4Activity>(activity);
 }
 @Override
 public void handleMessage(Message msg) {
  Main4Activity activity = weakReference.get();
  if (activity != null) {
  activity.tv.setText(String.valueOf(msg.arg1));
  }
 }
 }
 private MyHandler handler = new MyHandler(this);
 public void begin() {
 new Thread(new Runnable() {
  @Override
  public void run() {
   for (int i = 5; i > 0; i--) {
   Message msg = new Message();
   msg.what = UPDATE;
   msg.arg1 = i;
   handler.sendMessage(msg);
   try {
    Thread.sleep(1000);//休眠1秒
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
   Log.i("tag", Main4Activity.this + "-" + i);
   }
   //计时结束后跳转到其他界面
   startActivity(new Intent(Main4Activity.this, Main3Activity.class));
   //添加finish方法在任务栈中销毁倒计时界面，使新开界面在回退时直接退出而不是再次返回该界面
   finish();
  }
 }).start();
 }
 @Override
 protected void onDestroy() {
 super.onDestroy();
 handler.removeCallbacksAndMessages(null);
 Log.i("tag", "destory");
 }
}