ViewPager获取当前view

http://stackoverflow.com/questions/6807262/get-focused-view-from-viewpager/8638772#8638772

http://stackoverflow.com/questions/12854783/android-viewpager-get-the-current-view

http://stackoverflow.com/questions/16332034/not-able-to-get-the-current-view-in-viewpager/20186828#20186828