iOS Launch Files

A launch file (or image) provides a simple placeholder image that iOS displays when your app starts up. The placeholder image gives users the impression that your app is fast and responsive because it appears instantly and is quickly replaced by the first screen of your app. Every app must supply a launch file or at least one static image.

参考：［http://blog.csdn.net/yqmfly/article/details/43525397］

［https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/LaunchImages.html］