ViewPager 实现图片轮翻效果 - java 代码片段

Question

很多 App 都有这种效果，特别一些电商类的 App，顶部每隔几秒钟会向右翻页显示下张图片，用来作推广或者内容展示用的。今天来简单地模仿一下，还自带一个自动跳动的小功能（底部有几个小点，图片移动的时候，点的状态也在变化），用定时器来实现不难。

import java.util.ArrayList;  
import java.util.concurrent.Executors;  
import java.util.concurrent.ScheduledExecutorService;  
import java.util.concurrent.TimeUnit;  
import android.app.Activity;  
import android.os.Bundle;  
import android.os.Handler;  
import android.os.Message;  
import android.support.v4.view.PagerAdapter;  
import android.support.v4.view.ViewPager;  
import android.support.v4.view.ViewPager.OnPageChangeListener;  
import android.view.View;  
import android.view.ViewGroup;  
import android.widget.ImageView;  
import android.widget.TextView;  
public class MainActivity extends Activity {  
	private int imageIds[];  
	private String[] titles;  
	private ArrayList<ImageView> images;  
	private ArrayList<View> dots;  
	private TextView title;  
	private ViewPager mViewPager;  
	private ViewPagerAdapter adapter;  
	private int oldPosition = 0;//记录上一次点的位置  
	private int currentItem; //当前页面  
	private ScheduledExecutorService scheduledExecutorService;  
	@Override  
	public void onCreate(Bundle savedInstanceState) {  
		super.onCreate(savedInstanceState);  
		setContentView(R.layout.activity_main);  
		//图片 ID  
		imageIds = new int[]{  
			R.drawable.a,     
			R.drawable.b,     
			R.drawable.c,     
			R.drawable.d,     
			R.drawable.e      
		};  
		//图片标题  
		titles = new String[]{  
			"巩俐不低俗，我就不能低俗",   
			"扑树又回来啦！再唱经典老歌引万人大合唱",    
			"揭秘北京电影如何升级",     
			"乐视网 TV 版大派送",      
			"热血屌丝的反杀"  
		};  
		//显示的图片  
		images = new ArrayList<ImageView>();  
		for(int i =0; i < imageIds.length; i++){  
			ImageView imageView = new ImageView(this);  
			imageView.setBackgroundResource(imageIds[i]);  
			images.add(imageView);  
		}  
		//显示的点  
		dots = new ArrayList<View>();  
		dots.add(findViewById(R.id.dot_0));  
		dots.add(findViewById(R.id.dot_1));  
		dots.add(findViewById(R.id.dot_2));  
		dots.add(findViewById(R.id.dot_3));  
		dots.add(findViewById(R.id.dot_4));  
		title = (TextView) findViewById(R.id.title);  
		title.setText(titles[0]);  
		mViewPager = (ViewPager) findViewById(R.id.vp);  
		adapter = new ViewPagerAdapter();   
		mViewPager.setAdapter(adapter);  
		mViewPager.setOnPageChangeListener(new OnPageChangeListener() {  
			@Override  
			public void onPageSelected(int position) {  
				title.setText(titles[position]);  
				dots.get(oldPosition).setBackgroundResource(R.drawable.dot_normal);  
				dots.get(position).setBackgroundResource(R.drawable.dot_focused);  
				oldPosition = position;  
				currentItem = position;  
			}  
			@Override  
			public void onPageScrolled(int arg0, float arg1, int arg2) {  
			}  
			@Override  
			public void onPageScrollStateChanged(int arg0) {  
			}  
		});  
	}  
	private class ViewPagerAdapter extends PagerAdapter {  
		@Override  
		public int getCount() {  
			return images.size();  
		}  
		//是否是同一张图片  
		@Override  
		public boolean isViewFromObject(View arg0, Object arg1) {  
			return arg0 == arg1;  
		}  
		@Override  
		public void destroyItem(ViewGroup view, int position, Object object) {  
			view.removeView(images.get(position));  
		}  
		@Override  
		public Object instantiateItem(ViewGroup view, int position) {  
			view.addView(images.get(position));  
			return images.get(position);  
		}  
	}  
	@Override  
	protected void onStart() {  
		// TODO Auto-generated method stub  
		super.onStart();  
		scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();  
		//每隔 2 秒钟切换一张图片  
		scheduledExecutorService.scheduleWithFixedDelay(new ViewPagerTask(), 2, 2, TimeUnit.SECONDS);  
	}  
	//切换图片  
	private class ViewPagerTask implements Runnable {  
		@Override  
		public void run() {  
			currentItem = (currentItem +1) % imageIds.length;  
			//更新界面  
			handler.obtainMessage().sendToTarget();  
		}  
	}  
	private Handler handler = new Handler(){  
		@Override  
		public void handleMessage(Message msg) {  
			//设置当前页面  
			mViewPager.setCurrentItem(<span style="font-family: Arial, Helvetica, sans-serif;">currentItem</span><span style="font-family: Arial, Helvetica, sans-serif;">);</span>  
		}  
	};  
}