Positioning a view on top of a tableview using Auto Layout - ios

Question

I have a tableview in my storyboard that has its class set to my UITableView subclass which is named SPSExplanationTableView. There are no constraints set on this tableview in Interface Builder.
I am trying to programmatically create a UIView that displays in front of the tableview—which I know how to do (blog post link)—but that is sized and positioned using Auto Layout. This is my code:
#import "SPSExplanationTableView.h"
#interface SPSExplanationTableView()
#property (nonatomic, strong) UIView *explanationView;
#end
#implementation SPSExplanationTableView
- (void)awakeFromNib
{
[super awakeFromNib];
self.explanationView = [[UIView alloc] init];
self.explanationView.translatesAutoresizingMaskIntoConstraints = NO;
self.explanationView.backgroundColor = [UIColor blueColor];
[self addSubview:self.explanationView];
[self bringSubviewToFront:self.explanationView];
NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:self.explanationView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0f constant:150.0f];
[self.explanationView addConstraint:heightConstraint];
NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:self.explanationView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0f constant:200.0f];
[self.explanationView addConstraint:widthConstraint];
NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:self.explanationView
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self
attribute:NSLayoutAttributeCenterY
multiplier:1.0f constant:0.0f];
[self addConstraint:topConstraint];
NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:self.explanationView
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self
attribute:NSLayoutAttributeCenterX
multiplier:1.0f constant:0.0f];
[self addConstraint:leftConstraint];
#end
When I run the app it crashes with the following assertion failure:
*** Assertion failure in -[SPSExplanationTableView layoutSublayersOfLayer:],
/SourceCache/UIKit_Sim/UIKit-2935.137/UIView.m:8794
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Auto Layout still
required after executing -layoutSubviews. SPSExplanationTableView's
implementation of -layoutSubviews needs to call super.'
Taking the message literally and overriding layoutSubviews has no effect i.e. I still get the same crash.
- (void)layoutSubviews
{
[super layoutSubviews];
}
What's the correct way to implement what I'm trying to achieve?
For Aubada Taljo, here's the tableview in Interface Builder:
Update: I solved this myself in the end by not using Auto Layout! I overrode the layoutSubviews method in my SPSExplanationTableView class and set the center property of the explanationView to the centre of self's bounds, with some slight adjustments to the y-axis position to make it look how I wanted it.

Answer 1

This is crashing because UITableViews are not designed to do this. A UITableView is only concerned about its cells, the headers, maybe its background, and it has logic for this that doesn't use autolayout. So it will crash if you try to involve it in any constraints calculation between it and any subviews, e.g. this will also crash if you add a constraint between the cell and the table.
What I suggest you do is to add a superview that will contain both your table and the view that you want to overlay:
SuperviewWithConstraints
|
|-- YourTableViewWithConstraintsRelativeToSuperview
|
|-- YourOverlayWithConstraintsRelativeToSuperview
And set up the constraints there. Then make that superview as your view controller's view. You will have to move away from using the UITableViewController as the controlling class, though.

Answer 2

If you would take my advice and make your life easier, simply go to your storyboard in Interface Builder and set the correct constraints on the your table view, now go back to the code editor and in the UIViewController that owns your table view, write the view creation code in viewDidLoad e.g.
UIView* someView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.tableView.frame.size.width, self.tableView.frame.size.height)];
[self.view addSubView someView];
I guess this should be more than enough to solve your issue, now if you face any problems, move your code to viewDidLayoutSubViews in the UIViewController
Please tell me if you need more details but I use this way of creating dynamic controls all the time.