ViewHolder-by TomHawk

ViewHolder的作用主要是对自定义的Adapter进行一些性能优化。常见写法有两种:

一、直接写法：

直接在自定义的Adapter里面添加ViewHolder类以使用：

class ViewHolder{
         Button btn;
         ImageView iv;
         TextView tv;
         ...
     }

二、通用写法

public class ViewHolder {
    @SuppressWarnings("unchecked")
    public static <T extends View> T get(View view, int id) {
        SparseArray<View> viewHolder = (SparseArray<View>) view.getTag();
        if (viewHolder == null) {
            viewHolder = new SparseArray<View>();
            view.setTag(viewHolder);
        }
        View childView = viewHolder.get(id);
        if (childView == null) {
            childView = view.findViewById(id);
            viewHolder.put(id, childView);
        }
        return (T) childView;
    }
}