ViewDidAppear call more than once

Let use this code after application start (replace window.rootViewController) :

```
let slideMenuController = SlideMenuController(mainViewController: mainViewController, rightMenuViewController: rightMenuViewController)
window.rootViewController = slideMenuController
```

`mainViewController. viewDidAppear` is call twice on iOs 10 because `SlideMenuController .viewWillLayoutSubviews` is called more than once and its implementation is strange : each time it uses `setUpViewController` which calls `addChildViewController`.

To my point of view, it's not a good practice to call `addChildViewController` on the same child several times (this duplicates viewController life cycle events). Is there a good reason for this, or is this a bug ?