Android BaseAdapter

ListView显示与缓存机制：

     只会加载当前屏幕所要显示的数据。显示完成就会被回收到Recycler中。

 

 

 

BaseAdapter 基本结构：

     public int getCount();     // 适配器中数据集中数据的个数

     public Object getIten(int position);     //获取数据集中与指定索引对应的数据项

     public long getItemId(int position);     //获取指定行对应的ID

     public View getView(int position,View convertView,ViewGroup parent);     //获取每一个Item的显示内容

 

 

ViewHolder优化BaseAdapter:

          创建Bean对象，用于封装数据。

          在构造方法中初始化用于映射的数据LIST.

          创建ViewHolder类，创建布局映射关系。

          判断convertView,为空则创建，并设置TAG，否则通过TAG来取出ViewHolder

          给ViewHolder中的控件设置数据。

 

 

public class Adapter extends BaseAdapter{

 

        private List<ItemBean> list ;

        private LayoutInflater inflater ;

       

        public Adapter(List<ItemBean> list,Context context){

              list= this.list ;

               //context要使用当前的Adapter的界面对象 minflater布局装载器对象

               inflater=LayoutInflater. from(context);

       }

       

        @Override

        public int getCount() {

               // TODO Auto-generated method stub

               return list .size();

       }

 

        @Override

        public Object getItem(int position) {

               // TODO Auto-generated method stub

               return list .get(position);

       }

 

        @Override

        public long getItemId(int position) {

               // TODO Auto-generated method stub

               return position;

       }

 

        /**

        * 返回每一项所显示的内容

        */

        @Override

        public View getView(int position, View convertView, ViewGroup parent) {

              ViewHold viewHold;

               if(convertView==null){

                     viewHold= new ViewHold();

                     convertView= inflater.inflate(R.layout. item, null );

                     viewHold .ima geView=(ImageView) convertView.findViewById(R.id.IVimage );

                     viewHold. title= (TextView) convertView.findViewById(R.id.title );

                     viewHold. content=(TextView) convertView.findViewById(R.id.text );

                     convertView.setTag(viewHold);

              } else{

                     viewHold=(ViewHold) convertView.getTag();

                     

              }

              ItemBean bean= list.get(position);

              viewHold. imageView.setImageResource(bean.getImageid());

              viewHold. title.setText(bean.getTitle());

              viewHold. content.setText(bean.getText());

               return convertView;

       }

       

       

        class ViewHold{

               public ImageView imageView ;

               public TextView title ;

               public TextView content ;

       }

}