BaseAdapter&GridView

Adapter是连接后端数据和前端显示的适配器接口，是数据和UI（View）之间一个重要的纽带。在常见的View(ListView,GridView)等地方都需要用到Adapter。如下图直观的表达了Data、Adapter、View三者的关系：

BaseAdapter是一个abstrace class要使用时必须重写他的方法，注意这些方法都是抽象方法，分别生命在Adapter abstrace class中。分别是：

public int getCount()返回该Adapter中装载的资源的数量

public Object getItem(int position)从data set中取出指定poistion处的数据

public long getItemId(int position)return position处的item所在的row id

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

position:data set 中position处的数据，this data we want to view.

convertView:使用之前用convertView ? null判断，if can't covert to a view来装载数据然后显示的话，就需要创建一个新的view了；了；来装载数据.

parent: as the convertView's parent view and must attached to parent.

after call this function will return the view with data in the position  of  the adapter. 

点击时候的响应函数：

public abstract void onItemClick (AdapterView<?> parent, View view, int position, long id)

parent	The AdapterView where the click happened.发生click事件的那个AdapterView
view	The view within the AdapterView that was clicked (this will be a view provided by the adapter)
position	The position of the view in the adapter.
id	The row id of the item that was clicked.

ImageSwitcher: