ContentInset not updated when view is added as subviews - swift

Question

I'm making a photo browsing app, which the user can view the details and comments from the web of the photo being viewed. To do this I have a UIViewController (parentVC) with a segmented control that act as the switch between the details and comments, and the two UITableViewControllers that serve the details and comments. Storyboard of the view controllers in question.
To switch between views, the tableVCs are instantiated from the storyboard and added to the parentVCs as childViewController, and their views are added as subviews.
Since the segmentedControl are placed in the navigationController's navBar, I'd want the tableViews to play nice with the parentVC's navigationbar as well. Which when the first tableview (detailVC) is instantiated, its contentInset is automatically adjusted.
However, when the second tableview (commentsVC) is instantiated following a switch from the segmented control, it's contentInset is not set (in fact it's 0 for all edges), and the tableview is hidden behind the navBar. But when the device is rotated, the tableview adjust its insets and it works fine again.
Right now I suspect the problem has something to do with how automaticallyadjustsscrollviewinsets is done by iOS, since switching which childVC is present first would always set the first VC being presented's contentInset. I don't know if there are any methods I could trigger to set the second VC's contentInset when it's added.
So the question is, how do I have both the childVCs' contentInset set to respect the navigationBar in parentVC? Creating a UIEdgeInset is a workaround but it won't update itself when device orientation is changed. A more minor question would be how should I work with the layouts and insets of navigation controllers when the childVCs are instantiated programmatically so that they work as if they are linked in the storyboard itself.
The following is my code when instantiating the childVCs from the parentVC.
if index == 0 { //details
if detailsVC == nil {
detailsVC = storyboard?.instantiateViewControllerWithIdentifier("InfoPaneDetailsVC") as! InfoPaneDetailsVC
}
if commentsVC != nil {
commentsVC.view.removeFromSuperview()
commentsVC.removeFromParentViewController()
}
addChildViewController(detailsVC)
detailsVC.didMoveToParentViewController(self)
view.addSubview(detailsVC.view)
view.layoutSubviews()
} else if index == 1 { //comments
if commentsVC == nil {
commentsVC = storyboard?.instantiateViewControllerWithIdentifier("InfoPaneCommentsVC") as! InfoPaneCommentsVC
}
if detailsVC != nil {
detailsVC.view.removeFromSuperview()
detailsVC.removeFromParentViewController()
}
addChildViewController(commentsVC)
commentsVC.didMoveToParentViewController(self)
view.addSubview(commentsVC.view)
view.layoutSubviews()
}

Answer 1

the tableview is hidden behind the navBar. But when the device is rotated, the tableview adjust its insets and it
works fine again.
I can duplicate what you are seeing. I don't know why rotating the device gets rid of the underlap*. I can even start the app in landscape orientation, and the TableView will underlap the NavigationBar, then when I rotate to portrait the underlap disappears.
A couple of solutions work for me:
edgesForExtendedLayout = .None
navigationController?.navigationBar.translucent = false
If a ViewController's parent is a NavigationController (or a TabBarController), then two properties determine how the underlap works:
The ViewController's edgesForExtendedLayout property.
The NavigationBar's translucent property.
The edgesForExtendedLayout property has a default value of .All, which means that the ViewController's view will underlap all translucent bars.
You can check whether your NavigationBar is translucent like this:
import UIKit
class InfoViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
if navigationController?.navigationBar.translucent == true {
print("NavigationBar is translucent.")
}
if edgesForExtendedLayout == .All {
print("This ViewController's view will underlap a translucent NavigationBar.")
}
I get:
NavigationBar is translucent.
This ViewController's view will underlap a translucent NavigationBar.
The UINavigationBar docs say**,
Additionally, navigation bars are translucent by default. Turning the
translucency off or on does not affect buttons, since they do not have
backgrounds.
You can prevent the underlap like this:
import UIKit
class InfoViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
edgesForExtendedLayout = .None
}
.None tells the ViewController's view not to underlap any translucent bars. Or, you could use .Bottom, which means the view will only underlap a translucent bottom bar, i.e. not a translucent top bar. (To see the various values--or combinations of values--that you can assign to edgesForExtendedLayout check out the docs).
Or, you can prevent the underlap like this:
import UIKit
class InfoViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
navigationController?.navigationBar.translucent = false
}
The value of edgesForExtendedLayout only applies to translucent bars--a view will not underlap an opaque bar. If you don't want to be bothered with having to set translucent to false in your code, you can select the Navigation Bar in the storyboard, and in the Attributes Inspector uncheck Translucent.
* After rotating the device, I printed out edgesForExtendedLayout and the NavBar's translucent property and they didn't change:
class InfoViewController: UIViewController {
override func viewWillTransitionToSize(size: CGSize,
withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator)
{
super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
//executes before transition
coordinator.animateAlongsideTransition(//unlabeled first argument:
{ (UIViewControllerTransitionCoordinatorContext) -> Void in
//executes during transition
},
completion: { (UIViewControllerTransitionCoordinatorContext) -> Void in
//executes after transition
print("After rotating:")
if self.navigationController?.navigationBar.translucent == true {
print("NavigationBar is translucent.")
}
if self.edgesForExtendedLayout == .All {
print("This ViewController's view will underlap a translucent NavigationBar.")
}
}
)
}
--output:--
NavigationBar is translucent.
This ViewController's view will underlap a translucent NavigationBar.
After rotating:
NavigationBar is translucent.
This ViewController's view will underlap a translucent NavigationBar.
** If a NavigationBar has a background image, the value of the NavigationBar's translucent property will be set to true or false depending on the alpha of the image. See the Translucency section in the UINavigationBar docs.