前言

        网上有很多使用ViewPager实现左右滑动这一效果的资料，这些资料大多数都是将PagerAdapter中getCount()方法的返回值设为Integer.MAX_VALUE使用户看不到边界，然后在instantiateItem()方法中通过position%（要循环显示的数据集的长度）的方式取得对应的数据集。这样虽然可以做到无限循环，但是会有两个弊端：首先会创建大量对象，容易引起内存溢出（循环加载图片）从而影响性能；其次从第一页向右滑动的时候是无法滑动的。        今天给大家分享的是另一种实现方式：创建三个图片视图放入ViewPager中默认选中第二页，在接下来的滑动中每次滑动结束之后都将当前页码设置为第二页，然后通过判断是向左向右滑动来设置视图中的数据集，这样就可以实现无限循环了，而且只会创建三个图片视图对象。

示例源码

package com.viewpager; import java.util.ArrayList; import java.util.List; import android.os.Bundle; 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.app.Activity; public class MainActivity01 extends Activity implements OnPageChangeListener { private ViewPager viewPager; static final int arrays[] = { R.drawable.guide1, R.drawable.guide2, R.drawable.guide3, R.drawable.guide4, R.drawable.guide5 }; private List<ImageView> views; private int currentPage = 0; private ImageView imageView; private MyViewPagerAdapter viewPagerAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initWidget(); } private void initWidget() { viewPager = (ViewPager) findViewById(R.id.viewpager); views = new ArrayList<ImageView>(); for (int i = 0; i < 3; i++) { imageView = new ImageView(this); imageView.setLayoutParams(new ViewGroup.LayoutParams( ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT)); views.add(imageView); } initImageData(); viewPagerAdapter = new MyViewPagerAdapter(); viewPager.setAdapter(viewPagerAdapter); viewPager.setCurrentItem(1); viewPager.setOnPageChangeListener(this); } private void initImageData() { for (int i = 0; i < 3; i++) { imageView = views.get(i); if (i == 0) { imageView.setImageResource(arrays[arrays.length - 1]); } else { imageView.setImageResource(arrays[i - 1]); } } } class MyViewPagerAdapter extends PagerAdapter { @Override public int getCount() { // TODO Auto-generated method stub return views.size(); } @Override public boolean isViewFromObject(View arg0, Object arg1) { // TODO Auto-generated method stub return arg0 == arg1; } @Override public Object instantiateItem(ViewGroup container, int position) { imageView = views.get(position); container.addView(imageView); return imageView; } @Override public void destroyItem(ViewGroup container, int position, Object object) { // TODO Auto-generated method stub container.removeView((View) object); } } // 当滑动状态改变时调用 @Override public void onPageScrollStateChanged(int state) { // TODO Auto-generated method stub System.out.println("--onPageScrollStateChanged--state--:" + state); switch (state) { // 在滚动完成后 case ViewPager.SCROLL_STATE_IDLE: int currentItem = viewPager.getCurrentItem(); System.out.println("--currentItem--00--:" + currentItem); System.out.println("--currentPage--00--:" + currentPage); if (viewPager.getCurrentItem() == 1) { // 如果位置没有变终止循环 break; } if (viewPager.getCurrentItem() > 1) { currentPage++; } else { currentPage--; } System.out.println("--currentPage--11--:" + currentPage); if (currentPage == arrays.length) { currentPage = 0; } if (currentPage == -1) { currentPage = arrays.length - 1; } System.out.println("--currentPage--22--:" + currentPage); if (currentPage == 0) { views.get(0).setImageResource(arrays[arrays.length - 1]); } else { views.get(0).setImageResource(arrays[currentPage - 1]); } views.get(1).setImageResource(arrays[currentPage]); if (currentPage == arrays.length - 1) { views.get(2).setImageResource(arrays[0]); } else { views.get(2).setImageResource(arrays[currentPage + 1]); } viewPager.setCurrentItem(1, false); currentItem = viewPager.getCurrentItem(); System.out.println("--currentItem--11--:" + currentItem); break; } } // 当当前页面被滑动时调用 @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { // TODO Auto-generated method stub // System.out.println("--onPageScrolled--position--:" + position); } // 当新的页面被选中时调用 @Override public void onPageSelected(int position) { // TODO Auto-generated method stub System.out.println("--onPageSelected--position--:" + position); } }