Android 使用ViewPager真正实现左右无限滑动（附源码）

Posted 2022-11-28 mufeng_慕枫

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);