Limit UICollectionView height using inequality constraints and priorities - objective-c

Question

I have a collection view pinned to its superview bottom, left, and right edges and a text field pinned to superview top, left, and right. The collection view's height is increased in updateConstraints from the bottom up with a height constraint based on its content size as more items are added to it.
I'd like the collection view height to grow but not exceed the
bottom of the textField above it with an inequality constraint on the
collection view's top edge. Here's what I've tried:
self.topResistanceConstraint = [NSLayoutConstraint constraintWithItem:self.collectionView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationGreaterThanOrEqual
toItem:self.textField
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:0];
[self addConstraint:self.topResistanceConstraint];
CGSize size = self.collectionView.collectionViewLayout.collectionViewContentSize;
self.heightConstraint = [NSLayoutConstraint constraintWithItem:self.collectionView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0
constant:size.height];
[self addConstraint:self.heightConstraint];
This results in unsatisfiable constraints, and recovers (and actually appears to work), but it's not a good solution and doesn't work if the layout needs to adapt to a keyboard appearing or disappearing. Any suggestions how to create constraints or priorities to get this to work without breaking constraints?

Answer 1

After some trial and error, simply setting the heightConstraint to low priority works well. The topResistanceConstraint's priority is required, and prevents the collection view's top from exceeding the bottom of the text field.
self.heightConstraint = [NSLayoutConstraint constraintWithItem:self.collectionView attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0
constant:size.height];
// set a low priority on height
self.heightConstraint.priority = UILayoutPriorityLow;
[self addConstraint:self.heightConstraint];

Answer 2

The preferred solution for this problem is to create a height and top constraint
(top constrains related by "NSLayoutRelationGreaterThanOrEqual") for the collectionView in the storyboard and create the outlet for both.
After that get the collectionView item count and than dynamically calculate the height of the collectionView as below
NSInteger count = 5;
CGFloat collectionViewHeight = count/2 * cellHeight; // for collectionView with two(2) columns
CGFloat maxCollectionViewHeight = CGRectGetHeight(self.view.frame) - CGRectGetHeight(self.textField.frame) - CGRectGetMaxY(self.textField.frame);
if (collectionViewHeight < maxCollectionViewHeight ) {
self.heightConstraint.constant = collectionViewHeight;
} else {
self.topConstraint.constant = 20; // Min spacing between two views;
}