Adapter for ViewPager which reuse the item views

可复用View的PagerAdapter

package com.msyd.client.ui.viewadapter;

import java.util.ArrayList;
import java.util.List;

import android.support.v4.view.PagerAdapter;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;

/**
 * view pager adapter，复用view
 * 
 * @author viyu
 * 
 */
public abstract class ViewPagerAdapter extends PagerAdapter {

	private SparseArray<View> mPageViews = new SparseArray<View>();

	public ViewPagerAdapter() {
		super();
	}
	
	/**
	 * 获取view方法，子类实现这个方法来获取渲染View
	 * 
	 * @param convertView 如果是null则没有可复用的View，如果非null则是可复用的View
	 * @param position
	 * @return
	 */
	protected abstract View getView(View convertView, int position);
	

	@Override
	public int getItemPosition(Object object) {
	    return POSITION_NONE;
	}

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

	@Override
	public Object instantiateItem(ViewGroup container, int position) {
		// 获取复用的view给子类去用，没有可复用的view时为null
		View view = getView(pullViewFromPool(), position);
		// 记录该view以在destroyItem中能找到
		mPageViews.put(position, view);
		// 添加到view pager
		container.addView(view);
		return view;
	}

	@Override
	public void destroyItem(ViewGroup container, int position, Object object) {
		View view = mPageViews.get(position);
		// 把要删除的view放到pool里以供复用
		pushViewToPool(view);
		// 从view pager中删除
		container.removeView(view);
	}

	/****************** 复用view start ******************************/
	private List<View> mPageViewPool = new ArrayList<View>();

	private View pullViewFromPool() {
		View view = null;
		for (View v : mPageViewPool) {
			view = v;
			break;
		}
		if (view != null) {
			mPageViewPool.remove(view);
		}
		return view;
	}

	private void pushViewToPool(View view) {
		if (!mPageViewPool.contains(view)) {
			mPageViewPool.add(view);
		}
	}
	/****************** 复用view end ******************************/
}