app在4寸屏幕上显示只有3.5寸问题，上面下面都有一段黑色的空白区域。视图只占据了3.5寸320*480的空间。
问题解决方案：
参考：http://stackoverflow.com/questions/12518879/extend-app-for-iphone-5-best-practice
http://stackoverflow.com/questions/18913105/black-bars-showing-when-running-app-on-ios-7-4-inch-retina-display
Taking advantage of the full 4" screen in your apps seems to be as simple as adding a new Default image named Default-568h@2x.png with
size 640 x 1136. Xcode 4.5 will actually offer to do this for you automatically by adding a black image of the proper size and name to your project.
补全这三张图片，然后拉到项目中去。Default.png Default@2x.png Default-568h@2x.png