设置LaunchImageSource时,需要将图片调整成iPhone屏幕大小
iPhone4 640x480 3.5inch
iPhone5 640x1136 4inch
iPhone6 750x1334 4.7inch
iPhone6P 1080x1920 5.5inch
Launch Image Source
原文：http://www.cnblogs.com/visionary/p/4364527.html
