listView 优化 -ViewHolder

ViewHolder模式是提高ListView效率的一个很重要的方法，ViewHolder充分利用了ListView视图缓存机置，避免每次在getView()中都去通过findViewById()实例化控件，可以提高50%的效率，此模式很简单，只要在Adapter中定义一个内部类，并将布局中的控件作为成员变量。

public final class ViewHolder{
public ImageView img;
public TextView title;

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
HashMap<String, Object> Info = mList.get(position);
if(convertView == null){
holder = new ViewHolder();

                        //通过LayoutInflater实例化布局
convertView =  LayoutInflater.from(context).inflate(R.layout.item_list_select_car, null);
holder.img = (ImageView) convertView.findViewById(R.id.iv_item_select_car_brand);
holder.title = (TextView) convertView.findViewById(R.id.tv_item_select_car_name);
convertView.setTag(holder);//保存到缓存中
}
else{
//通过tag找到缓存布局
holder = (ViewHolder) convertView.getTag();
}

if(Info != null){

String icon = (String) Info.get("icon");
String brandName = (String) Info.get("brandName");

holder.title.setText(brandName);
setImageLoader(holder.img,Constants.ICON_HEAD+icon);
}

return convertView;
}