17.说一下AppDelegate的几个方法？从后台到前台调用了哪些方法？第一次启动调用了哪些方法？从前台到后台调用了哪些方法？

整个《面试题》都是对[2017年6月iOS招人心得(附面试题)]的整理
  这主要是问App的生命周期。

1.点击App图标(App没有在后台运行)

  1.didFinishLaunchingWithOptions
  2.applicationDidBecomeActive

2.从后台到前台

  1.applicationWillEnterForeground
  2.applicationDidBecomeActive

3.从前台到后台

  1.applicationWillResignActive
  2.applicationDidEnterBackground

4.通过URLScheme打开App

  1.applicationWillEnterForeground
  2.

- (BOOL)application:(UIApplication *)application
                    openURL:(NSURL *)url
          sourceApplication:(NSString *)sourceApplication
                 annotation:(id)annotation

  3.applicationDidBecomeActive