Android 使用ViewPager实现无限无缝循环

做这个之前 百度了一些资料大多数都是将count设置为integerMax 然后通position%count 方式取得对应的数据集 这样虽然可以做到无限循环 但是有两个弊端 首先会创建大量对象,性能方面肯定是不好,其次是从第一页向右边滑的时候是无法滑动的。
今天给大家分享个实现思路如下图

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.

swift代码实现

之前代码不严谨这里做下更新 方便有需要的童鞋
下面是代码 实现

package com.cn.gank_io.activity;
import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import com.bumptech.glide.Glide;
import java.util.ArrayList;
import java.util.List;

public class BannerAdapter extends PagerAdapter
    implements ViewPager.OnPageChangeListener, View.OnClickListener {

  private ViewPager viewPager;

  private final static int PAGE = 0x03;
  private final static int INDEX = 1;
  private final static int START_INDEX = 0;

  private List<String> dataSource;
  private ArrayList<ImageView> views;
  private Context context;
  //记录真正的位置
  private int currentPage;

  private ItemClickListener itemClickListener;

  public BannerAdapter(Context context, ViewPager viewPager, List<String> dataSource) {
    this.context = context;
    this.dataSource = dataSource;
    this.viewPager = viewPager;
    viewPager.clearOnPageChangeListeners();
    viewPager.addOnPageChangeListener(this);
    if (null == dataSource || dataSource.isEmpty()) return;
    initView(false);
    setDataToView();
  }

  public void setItemClickListener(ItemClickListener itemClickListener) {
    this.itemClickListener = itemClickListener;
  }

  public void nextPage() {
    if (null == dataSource || dataSource.isEmpty()) return;
    //因为位置始终为1 那么下一页就始终为2
    viewPager.setCurrentItem(2, true);
  }

  /**
   * 初始化图形控件
   * 为image填充数据
   */
  private void initView(boolean isScale) {
    views = new ArrayList<>();
    if (dataSource.size() == 1) {
      views.add(getImageView());
      return;
    }
    for (int i = 0; i < PAGE; i++) {
      views.add(getImageView());
    }
  }

  private void setDataToView() {
    int size = dataSource.size();
    if (size == 1) {
      Glide.with(context).load(dataSource.get(0)).into(views.get(0));
      return;
    }
    for (int i = 0; i < PAGE; i++) {
      int index = 0;
      if (0 == i) {
        index = size - 1;
      } else {
        index = i - 1;
      }
      Glide.with(context).load(dataSource.get(index)).into(views.get(i));
    }
  }

  public void showIndex(int index) {
    if (null == dataSource || dataSource.isEmpty()) return;
    if (index == dataSource.size()) {
      currentPage = 0;
    } else {
      currentPage = index;
    }
    if (dataSource.size() == 1) {
      Glide.with(context).load(dataSource.get(0)).into(views.get(0));
    } else {
      indexChange();
    }
  }

  /**
   * get imageView
   */
  private ImageView getImageView() {
    ImageView imageView = new ImageView(context);
    imageView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
        ViewGroup.LayoutParams.MATCH_PARENT));
    imageView.setClickable(true);
    imageView.setOnClickListener(this);
    imageView.setScaleType(ImageView.ScaleType.FIT_XY);
    return imageView;
  }

  @Override public int getCount() {
    return (null == views) ? 0 : views.size();
  }

  @Override public boolean isViewFromObject(View view, Object object) {
    return view == object;
  }

  @Override public Object instantiateItem(ViewGroup container, int position) {
    ImageView imageView = views.get(position);
    if (null != imageView.getParent()) {
      ViewGroup viewGroup = (ViewGroup) imageView.getParent();
      viewGroup.removeView(imageView);
    }
    container.addView(imageView);
    return imageView;
  }

  @Override public void destroyItem(ViewGroup container, int position, Object object) {
    container.removeView((View) object);
  }

  @Override
  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    if (dataSource.size() == 1) {
      return;
    }
    if (0 != positionOffset) return;

    if (position == INDEX) {
      return;
    }
    if (position > INDEX) {
      currentPage++;
    } else {
      currentPage--;
    }
    if (currentPage == -INDEX) {
      currentPage = dataSource.size() - INDEX;
    } else if (currentPage == dataSource.size()) {
      currentPage = START_INDEX;
    }
    indexChange();
  }

  private void indexChange() {
    if (currentPage == START_INDEX) {
      Glide.with(context).load(dataSource.get(dataSource.size() - 1)).into(views.get(0));
    } else {
      Glide.with(context).load(dataSource.get(currentPage - 1)).into(views.get(0));
    }
    Glide.with(context).load(dataSource.get(currentPage)).into(views.get(1));
    if (currentPage == dataSource.size() - 1) {
      Glide.with(context).load(dataSource.get(0)).into(views.get(2));
    } else {
      if (currentPage == 0 && dataSource.size() == 2) {
        Glide.with(context).load(dataSource.get(dataSource.size() - 1)).into(views.get(2));
      } else {
        Glide.with(context).load(dataSource.get(currentPage+1)).into(views.get(2));
      }
    }
    viewPager.setCurrentItem(1, false);
  }

  @Override public void onPageSelected(int position) {
  }

  @Override public void onPageScrollStateChanged(int state) {
  }

  @Override public void onClick(View v) {
    if (null!=itemClickListener)itemClickListener.onItemClick(currentPage);
  }

  public int getCurrentPage() {
    return currentPage;
  }

  public interface ItemClickListener {
    void onItemClick(int index);
  }
}