- public class MyViewPagerAdapter extends PagerAdapter {
- //显示的数据
- private List<DataBean> datas = null;
- private LinkedList<View> mViewCache = null;
- private Context mContext ;
- private LayoutInflater mLayoutInflater = null;
- public MyViewPagerAdapter(List<DataBean> datas, Context context) {
- super();
- this.datas = datas;
- this.mContext = context ;
- this.mLayoutInflater = LayoutInflater.from(mContext) ;
- this.mViewCache = new LinkedList<>();
- }
- @Override
- public int getCount() {
- Log.e("test","getCount ");
- return this.datas.size();
- }
- @Override
- public int getItemPosition(Object object) {
- Log.e("test","getItemPosition ");
- return super.getItemPosition(object);
- }
- @Override
- public Object instantiateItem(ViewGroup container, int position) {
- Log.e("test","instantiateItem " + position);
- ViewHolder viewHolder = null;
- View convertView = null;
- if(mViewCache.size() == 0){
- convertView = this.mLayoutInflater.inflate(R.layout.viewadapter_item_layout ,
- null ,false);
- TextView textView = (TextView)convertView.findViewById(R.id.view_pager_item_textview);
- viewHolder = new ViewHolder();
- viewHolder.textView = textView;
- convertView.setTag(viewHolder);
- }else {
- convertView = mViewCache.removeFirst();
- viewHolder = (ViewHolder)convertView.getTag();
- }
- viewHolder.textView.setText(datas.get(position).title);
- viewHolder.textView.setTextColor(Color.YELLOW);
- viewHolder.textView.setBackgroundColor(Color.GRAY);
- container.addView(convertView ,ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT );
- return convertView;
- }
- @Override
- public void destroyItem(ViewGroup container, int position, Object object) {
- Log.e("test","destroyItem " + position);
- View contentView = (View) object;
- container.removeView(contentView);
- this.mViewCache.add(contentView);
- }
- @Override
- public boolean isViewFromObject(View view, Object o) {
- Log.e("test","isViewFromObject ");
- return view == o;
- }
- public final class ViewHolder{
- public TextView textView ;
- }
- }
首先需要了解ViewPager的Adapter各个方法的回调机制。
这里主要看两个方法:instantiateItem()和destroyItem()。
instantiateItem()方法,是在滑动到一个新的ViewItem的时候被调用的,而destroyItem()是在当用户滑到第3个ViewItem的时候被调用,在这个时候会先调用这个方法来回收第一个ViewItem,然后在调用instantiateItem()方法来实例化第3个ViewItem。可以在adapter的各个回调方法中打出log来看这个方法被调用的时机。
利用上面所说的机制,就可以在destroyItem()的时候将要被remove掉的view回收起来,然后在instantiateItme()的时候重复利用这个view。这样,就只会有3个ViewHolder实例存在。即当前显示的,还有上一个Item和下一个Item。