切換 iOS App 時回到首頁，會用下列兩種方式
applicationDidBecomeActive(第一次執行也會觸發...etc)
applicationWillEnterForeground(只有從背景回到前景才會觸發)
這裡用applicationWillEnterForeground比較適合。
- (void)applicationWillEnterForeground:(UIApplication *)application
{
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle: nil];
UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"IntroViewController"];
self.window.rootViewController = vc;
}
storyboardWithName: Main.storyboard 大小寫有差
instantiateViewControllerWithIdentifier: ViewController's Storyboard ID
