storyboard兼容版本处理
//storyboard版本兼容

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{  // 1  UIStoryboard *mainStoryboard = nil;  if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"6.0")) {    mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];  } else {    mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard-legacy" bundle:nil];  }   // 2  self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];  self.window.rootViewController = [mainStoryboard instantiateInitialViewController];  [self.window makeKeyAndVisible];   return YES;}