andorid 多线程handler用法

<?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: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="com.hanqi.application3.UIActivity7"
    android:orientation="vertical">

    <AutoCompleteTextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="自动完成文本编辑框"
        android:id="@+id/actv_1"
        android:completionThreshold="1"/>
    <!--completionThreshold 提示所需要的字符-->
    <Spinner
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/sp_1">

    </Spinner>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="状态栏提示"
        android:onClick="notification_onClick"/>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/da2"
        android:id="@+id/iv_3"/>
</LinearLayout>

package com.hanqi.application3;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.Toast;

import java.util.Timer;
import java.util.TimerTask;


public class UIActivity7 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ui7);

        AutoCompleteTextView actv_1 = (AutoCompleteTextView)findViewById(R.id.actv_1);
        //设置自动完成的数据源

        String[] strings = {"China","Child","Chile","Chinese","Add","All","Class","Ddp"};
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,R.layout.layout_array,strings);

        actv_1.setAdapter(arrayAdapter);

        //下拉列表
        String[] strings1 = {"China","Child","Chile","Chinese","Add","All","Class","Ddp"};
        ArrayAdapter<String> arrayAdapter1 = new ArrayAdapter<String>(this,R.layout.layout_array,strings1);
        Spinner sp1= (Spinner)findViewById(R.id.sp_1);

        sp1.setAdapter(arrayAdapter1);

        sp1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(UIActivity7.this, "position ="+position, Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

                Toast.makeText(UIActivity7.this, "什么也没选", Toast.LENGTH_SHORT).show();

            }
        });

        //handler
        final ImageView iv3 = (ImageView)findViewById(R.id.iv_3);


        final int[] iImageid = {R.drawable.da1,R.drawable.da2,R.drawable.da3,R.drawable.da4};


        //继承Handler
        final Handler handler = new Handler()
        {
            int i = 0;
            //处理消息的回调方法
            //重写
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                //判断消息的类别
                if(msg.what ==1)
                {
                    //切换图片
                    iv3.setImageResource(iImageid[i++ % iImageid.length]);
//                    i++;
//                    if(i==10)
//                    {
//                        i=0;
//                    }

                }
            }
        };
        //在新线程发送消息
        //定式循环发送
        //定时器：启动新线程，定时执行代码
        new Timer().schedule(new TimerTask() {
            @Override
            public void run() {
                //发送消息
                //空消息
                handler.sendEmptyMessage(1);



            }
        },1000,2000);



    }
    public void notification_onClick(View v)
    {
        //1.获取状态栏消息管理器
        NotificationManager nm  = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);

        //3.构建意图
        Intent intent = new Intent(this,UIActivity2.class);

        //4.获取PendingIntent
        PendingIntent pendingIntent = PendingIntent.getActivity(this,0,intent,0);

        //2.构建消息   方法链调用
        Notification nt = new Notification.Builder(this)
                .setContentTitle("这是一个通知")
                .setContentText("这是通知内容：点击打开新的界面 ")
                .setTicker("新通知")
                .setSmallIcon(R.drawable.da1)//图片
                .setAutoCancel(true)
                .setDefaults(Notification.DEFAULT_ALL)//声音
                .setContentIntent(pendingIntent)

                .build();
        //交给管理器，发出消息
        nm.notify(0,nt);

    }
}