iOS Autolayout setting height constraint to zero leads to invalid layout

Question

I have following layout with AutoLayout enabled:

UIView
  UITableView

I have following constraints (only important here, rest are ommited):

|-(17)-[UITableView:0x15bfc200]  priority 1000 (Top space to container)
[UITableView:0x15bfc200]-(17)-|  priority 1000 (Bottom space to container)
[UITableView:0x15bfc200](=20)    priority 750  (TableView height)

When I'm trying to set height to zero (ex, it has no content) app stops with exception:

Probably at least one of the constraints in the following list is one you don't want...blah blah blah...

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x1559bf40 V:[UITableView:0x15bfc200]-(17)-|   (Names: '|':UITableViewCellContentView:0x1559b330 )>

Currently, I set height using the following code:

heightConstraint.constant = 0;

What is the correct way to set tableView height to zero? Should I lower the priority of some constraint?

Answer 1

I think the problem is that the outer UIView is a specific size. Its height is 54 points, so when you initially set up your constraints they work. But when you change the height to 0, the math doesn't work: 17 + 0 + 17 != 54.

I'm not 100% sure what your goal for this small tableview is, but I think you should be able to position it with just a top constraint and a height constraint (no bottom constraint needed). This will remove the requirement that your constraints add up to the height of the superview.