Working with NSLayoutConstraint

UIView+Constraints.h

//
//  UIView+Constraints.h
//
//  Created by Konstantin Simakov
//

#import <Foundation/Foundation.h>

@interface UIView (Constraints)

- (NSLayoutConstraint *)constraintByAttribute:(NSLayoutAttribute)attribute;
- (NSLayoutConstraint *)constraintByAttribute:(NSLayoutAttribute)attribute toView:(UIView *)view;

@end

UIView+Constraints.m

//
//  UIView+Constraints.m
//
//  Created by Konstantin Simakov
//

#import "UIView+Constraints.h"

@implementation UIView (Constraints)

- (NSLayoutConstraint *)constraintByAttribute:(NSLayoutAttribute)attribute
{
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"firstAttribute = %d", attribute];
    NSArray *filteredArray = [self.constraints filteredArrayUsingPredicate:predicate];
    if (filteredArray.count == 0) {
        return nil;
    }
    NSLayoutConstraint *constraint =  [filteredArray objectAtIndex:0];
    return constraint;
}

- (NSLayoutConstraint *)constraintByAttribute:(NSLayoutAttribute)attribute toView:(UIView *)view
{
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"firstAttribute = %d", attribute];
    NSArray *filteredArray = [self.constraints filteredArrayUsingPredicate:predicate];
    predicate = [NSPredicate predicateWithFormat:@"firstItem = %@", view];
    NSArray *secondFilteredArray = [filteredArray filteredArrayUsingPredicate:predicate];
    if (secondFilteredArray.count == 0) {
        predicate = [NSPredicate predicateWithFormat:@"secondItem = %@", view];
        secondFilteredArray = [filteredArray filteredArrayUsingPredicate:predicate];
    }
    if (secondFilteredArray.count == 0) {
        return nil;
    }
    NSLayoutConstraint *constraint =  [secondFilteredArray objectAtIndex:0];
    return constraint;
}

@end