基础元素的创建、关联与事件循环启动。
app\window\event\delegate\life circle
Flowchart
Flowchart of the default app launch sequence in iOS as of Xcode 4.2 for a non-storyboarded app. Feel free to share this image under a Creative Commons Attribution license (CC-BY). In a storyboarded app,
UIApplicationMain() would additionally initiate the loading of the app's main storyboard file, which in turn would create the window and initial view controller.