Eyal Eyal - 1 month ago 12
Objective-C Question

Auto Layout and "Hide bottom bar when pushed"

My app's (simplified) structure is this:

UITabBarController
with one
UINavigationController
holding a
UITableViewController
as root view controller.

when tapping one of the table view controller cells, I push a regular
UIViewController
(lets call it VC) end hiding the bottom tab bar. (using the "Hide bottom bar when pushed" flag)

In storyboard I added a regular
UIView
subclass to VC that look like a bottom bar, and I use Auto Layout to pin it to the bottom of the VC view.

The problem

when I push VC it takes a second for this view to pin to the bottom, it looks like auto layout pin it to the bottom as if the tab bar is not hidden and after a sec it recognise that the tab bar is hidden and moves it to the real bottom of the view.

I know its not the best explanation, so I added a very simple project to demonstrate the issue.

Answer

The problem is with this specific constraint which is between the view and the top of the bottom layout guide.

enter image description here

Select the constraint and edit its "Second Item" property

enter image description here

Here you need to choose bottom

enter image description here

Once you have that, the pink view is not influenced by layout guide anymore. The layout guide seem to acknowledge that the tab bar is hidden only after the root view of the pushed view controller is in the bounds of main screen and this happens only when the animation is finished.

And that is the reason the view hierarchy needs to be laid out again which causes the unwanted animation.

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