public interface SpinnerAdapter implements Adapter Class Overview Extended Adapter that is the bridge between a Spinner and its data. A spinner adapter allows to define two different views: one that shows the data in the spinner itself and one that shows the data in the drop down list when the spinner is pressed. SpinnerAdapter是绑定Data和Spinner的适配器. 它只申明了一个方法：
Get a View that displays in the drop down popup the data at the specified position in the data set.
参数（只是定义用于下拉时的显示的接口） position index of the item whose view we want. convertView the old view to reuse, if possible. Note: You should check that this view is non-null and of an appropriate type before using. If it is not possible to convert this view to display the correct data, this method can create a new view. parent the parent that this view will eventually be attached to Returns * a View corresponding to the data at the specified position. 实现它的类： BaseAdapter:（implements ListAdapter SpinnerAdapter） ArrayAdapter<T> CursorAdapter ResourceCursorAdapter SimpleCursorAdapter SimpleAdapter 实现它的接口： 无