Android必学-BaseAdapter的使用与优化

数据适配器——BaseAdapter
可以自定义View或者利用参数中的convertView

没有任何优化处理，每次都创建新的View，设置控件，效率极其低下

``` @Override
public View getView(int position, View convertView, ViewGroup parent) {
//逗比式（没有利用到ListView的缓存机制）//
View view = mInflater.inflate(R.layout.item,null);//装载到item中的布局文件
ImageView imageView = (ImageView) view.findViewById(R.id.iv_image);
TextView title = (TextView) view.findViewById(R.id.iv_title);
TextView content = (TextView) view.findViewById(R.id.iv_content);
ItemBean bean = mList.get(position);
imageView.setImageResource(bean.ItemImage);
title.setText(bean.ItemTitle);
content.setText(bean.ItemContent);
return view;
//逗比式//////////////////////////
}

二、普通式
-----
利用了ListView的缓存特性，如果没有缓存才创建新的View。算入门，但是findViewById依然会浪费大量时间

@Override
public View getView(int position, View convertView, ViewGroup parent) {
//普通式////////////////////
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item, null);
}
ImageView imageView = (ImageView) convertView.findViewById(R.id.iv_image);
TextView title = (TextView) convertView.findViewById(R.id.iv_title);
TextView content = (TextView) convertView.findViewById(R.id.iv_content);
ItemBean bean = mList.get(position);
imageView.setImageResource(bean.ItemImage);
title.setText(bean.ItemTitle);
content.setText(bean.ItemContent);
return content;
//普通式////////////////////

三、文艺式
-----

不仅利用了ListView的缓存，更通过ViewHolder类来实现显示数据的视图的缓存，避免多次通过findViewById寻找控件（这是最号的写法）
    1>创建内部类ViewHolder 
    2>判断convertView是否为空
    3>通过setTag将ViewHolder与convertView绑定

   //文艺式///////////////////
    ViewHolder viewHolder;
    if (convertView == null) {
        viewHolder = new ViewHolder();
        convertView = mInflater.inflate(R.layout.item, null);
        viewHolder.imageView = (ImageView) convertView.findViewById(R.id.iv_image);
        viewHolder.title = (TextView) convertView.findViewById(R.id.iv_title);
        viewHolder.content = (TextView) convertView.findViewById(R.id.iv_content);
        convertView.setTag(viewHolder);
    } else {
        viewHolder = (ViewHolder)convertView.getTag();
    }
    ItemBean bean = mList.get(position);
    viewHolder.imageView.setImageResource(bean.ItemImage);
    viewHolder.title.setText(bean.ItemTitle);
    viewHolder.content.setText(bean.ItemContent);
    return convertView;
    //文艺式///////////////////
}

class ViewHolder {
    public ImageView imageView;
    public TextView title;
    public TextView content;
}