NSLayoutConstraint with a two possible states and a flag to toggle between them

ToggleConstraint.m

#import <UIKit/UIKit.h>

/// This constraint could be toggled between two values (min/max) by `enlarged` flag
@interface ToggleConstraint : NSLayoutConstraint

/**
 Max size of the height/width/offset/etc.
 Think about it as some UI element can change it's size between min and max values.
 */
@property (nonatomic, assign) IBInspectable BOOL enlarged;

@property (nonatomic, assign) IBInspectable CGFloat minValue;
@property (nonatomic, assign) IBInspectable CGFloat maxValue;

@end

@implementation FWToggleConstraint

#pragma mark - Init

+ (instancetype)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(id)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c {
    ToggleConstraint *constraint = [super constraintWithItem:view1 attribute:attr1 relatedBy:relation toItem:view2 attribute:attr2 multiplier:multiplier constant:c];
    [constraint initDefaultValues];
    [constraint updateConstant];
    return constraint;
}

- (id)awakeAfterUsingCoder:(NSCoder *)aDecoder {
    id response = [super awakeAfterUsingCoder:aDecoder];
    [self initDefaultValues];
    [self updateConstant];
    return response;
}

- (void)initDefaultValues {
    _enlarged = NO;
    _minValue =
    _maxValue = 0.;
}

#pragma mark - Bindings

- (void)setEnlarged:(BOOL)enlarged {
    BOOL changed = (_enlarged != enlarged);
    _enlarged = enlarged;

    if (changed) {
        [self updateConstant];
    }
}

- (void)setMinValue:(CGFloat)value {
    BOOL changed = (_minValue != value);
    _minValue = value;

    if (changed && !self.enlarged) {
        [self updateConstant];
    }
}

- (void)setMaxValue:(CGFloat)value {
    BOOL changed = (_maxValue != value);
    _maxValue = value;

    if (changed && self.enlarged) {
        [self updateConstant];
    }
}

- (void)updateConstant {
    CGFloat constant = (self.enlarged) ? self.maxValue : self.minValue;
    [super setConstant:constant];

    [(UIView *)self.firstItem setNeedsLayout];
    [(UIView *)self.secondItem setNeedsLayout];
}

@end

ToggleConstraint.swift

import UIKit

class ToggleConstraint: NSLayoutConstraint {
    @IBInspectable var minValue: CGFloat = 0 {
        didSet {
            if oldValue != minValue {
                updateConstant()
            }
        }
    }
    @IBInspectable var maxValue: CGFloat = 0 {
        didSet {
            if oldValue != maxValue {
                updateConstant()
            }
        }
    }
    @IBInspectable var enlarged: Bool = false {
        didSet {
            if oldValue != enlarged {
                updateConstant()
            }
        }
    }

    override func awakeAfterUsingCoder(aDecoder: NSCoder) -> AnyObject? {
        let response = super.awakeAfterUsingCoder(aDecoder)
        updateConstant()
        return response
    }

    private func updateConstant() {
        super.constant = enlarged ? maxValue : minValue

        (firstItem as? UIView)?.setNeedsLayout()
        (secondItem as? UIView)?.setNeedsLayout()
    }
}