Collapsable Tableview with Dynamic sizing cells - ios

Question

I've been trying to follow this github tutorial, however instead of having static cells, they need to be dynamic since I don't know the height at compile time.
In the tableViewController I have set the heightForRowAt to be 0 or UITableViewAutomaticDimension depending if the section is collapsed or not. Similar with the estimatedHeightForRowAtthe value is 0 or a higher value if it's expanded.
Getting to the problem now, I have subclassed the UITableViewCell and when the cellForRowAt is called it will add a subview like the following:
override func addSubview(_ view: UIView) {
guard view != nil else {return}
for view in self.subviews {
view.removeFromSuperview()
}
super.addSubview(view)
//view.applyLeadingAndTrailingPinConstraint(toSuperview: 0)
//view.applyTopAndBottomPinConstraint(toSuperview: 0)
let addedView = self.subviews[0]
let bottom = NSLayoutConstraint(item: addedView, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1, constant: 0)
bottom.priority = 750
bottom.isActive = true
NSLayoutConstraint(item: addedView, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: addedView, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: addedView, attribute: .trailing, relatedBy: .equal, toItem: self, attribute: .trailing, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: addedView, attribute: .centerX, relatedBy: .equal, toItem: self, attribute: .centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: addedView, attribute: .centerY, relatedBy: .equal, toItem: self, attribute: .centerY, multiplier: 1, constant: 0).isActive = true
//NSLayoutConstraint.reportAmbiguity(v: self)
if addedView.hasAmbiguousLayout {
print("Horizontal: \(addedView.constraintsAffectingLayout(for: .horizontal))")
print("Vertical: \(addedView.constraintsAffectingLayout(for: .vertical))")
print("Trace: \(addedView.value(forKey: "_autolayoutTrace"))")
}
//addedView.exerciseAmbiguityInLayout()
//print("self: \(self.frame), subview: \(self.subviews[0].frame)")
}
As you may see, the problem is that there's an ambiguity with the constraints, hence the hasAmbigousLayout. When the view is collapsed there is no error. However when I expand the view, which has also a height constraint, the ambiguity happens. The following is the output of the 3 print statements inside hasAmbigousLayout:
Horizontal: []
Vertical: [<NSLayoutConstraint:0x60800028ea10 UIView:0x7fcfe856a790.height == 100 (active)>]
Trace: Optional(
•ViraVira_Info.WellnessCell:0x7fcfe8859a00'cell', MISSING HOST CONSTRAINTS
| *UIView:0x7fcfe856a790- AMBIGUOUS LAYOUT for UIView:0x7fcfe856a790.minX{id: 776}, UIView:0x7fcfe856a790.minY{id: 771}, UIView:0x7fcfe856a790.Width{id: 778}
Legend:
* - is laid out with auto layout
+ - is laid out manually, but is represented in the layout engine because translatesAutoresizingMaskIntoConstraints = YES
• - layout engine host)
I have tried to lower the bottom constraint priority as sugested in this question. Also I have tried many other sites, which I sadly lost track of.
The result in the app is that the view does not even show up, since it should have a red background, also when i try to print the frame of the subview, the width is 0 which seems odd.
I probably made a silly mistake with the constraint but after 2 days trying I still can't figure it out.
Thanks for your time
-Jorge

Answer 1

There are several issues to note (and may be part of the problem):
override func addSubview(_ view: UIView) -> I don't think thats the right place for your code. I develop several years now iOS and there was never a reason to override that method. View layout should be done in Interface Builder or in the parent view.
guard view != nil else {return} -> should give you a warning, because view is not an optional (UIView?), so it can't be nil. This check does simply nothing useful.
for view in self.subviews { view.removeFromSuperview() } super.addSubview(view) -> This will remove every previously added view, the last added view will win the race, thats completely unexpected by the caller of addSubview - If a cell adds more than one subview this will cause trouble and headache.
let addedView = self.subviews[0] -> must be equal view, so why not using view in the later code?
6 * NSLayoutConstraint -> A view is normally positioned by 4 constraints, 2 vertical and 2 horizontal - I think you should remove the last two (center constraints) - That may be your problem.
Try to refactor your code...