Use XibLayoutConstraintHelper to change the constraint of a view from to the Top Guide instead of Top View, especially useful for xib file development.

LayoutConstraintBuilder.swift

//
//  Created by Khanh Le Do on 16/4/16.
//  Copyright © 2016 kloc. All rights reserved.
//

import Foundation
import UIKit

public class LayoutConstraintBuilder {
    
    private var mOrigin: NSLayoutConstraint?
    
    private var mFirstItem: AnyObject?
    private var mSecondItem: AnyObject?
    private var mPriority: UILayoutPriority?
    private var mRelation: NSLayoutRelation?
    private var mMultiplier: CGFloat?
    private var mConstant: CGFloat?
    private var mFirstAttribute: NSLayoutAttribute?
    private var mSecondAttribute: NSLayoutAttribute?
    
    public init() {
        // Nothing to init
    }
    
    public init(origin: NSLayoutConstraint) {
        self.mOrigin = origin
    }
    
    public func setFirstItem(firstItem: AnyObject?) -> LayoutConstraintBuilder {
        self.mFirstItem = firstItem
        return self
    }
    
    public func setSecondItem(secondItem: AnyObject?) -> LayoutConstraintBuilder {
        self.mSecondItem = secondItem
        return self
    }
    
    public func setPriority(priority: UILayoutPriority?) -> LayoutConstraintBuilder {
        self.mPriority = priority
        return self
    }
    
    public func setRelation(relation: NSLayoutRelation?) -> LayoutConstraintBuilder {
        self.mRelation = relation
        return self
    }
    
    public func setMultiplier(multiplier: CGFloat?) -> LayoutConstraintBuilder {
        self.mMultiplier = multiplier
        return self
    }
    
    public func setConstant(constant: CGFloat?) -> LayoutConstraintBuilder {
        self.mConstant = constant
        return self
    }
    
    public func setFirstAttribute(firstAttribute: NSLayoutAttribute?) -> LayoutConstraintBuilder {
        self.mFirstAttribute = firstAttribute
        return self
    }
    
    public func setSecondAttribute(secondAttribute: NSLayoutAttribute?) -> LayoutConstraintBuilder {
        self.mSecondAttribute = secondAttribute
        return self
    }
    
    public func build() -> NSLayoutConstraint {
        let priority = (self.mPriority != nil ? self.mPriority : self.mOrigin?.priority)
        let relation = (self.mRelation != nil ? self.mRelation : self.mOrigin?.relation)
        let multiplier = (self.mMultiplier != nil ? self.mMultiplier : self.mOrigin?.multiplier)
        let constant = (self.mConstant != nil ? self.mConstant : self.mOrigin?.constant)
        let firstAttribute = (self.mFirstAttribute != nil ? self.mFirstAttribute : self.mOrigin?.firstAttribute)
        let secondAttribute = (self.mSecondAttribute != nil ? self.mSecondAttribute : self.mOrigin?.secondAttribute)
        
        let firstItem = (self.mFirstItem != nil ? self.mFirstItem : self.mOrigin?.firstItem)
        let secondItem = (self.mSecondItem != nil ? self.mSecondItem : self.mOrigin?.secondItem)
        
        let ret = NSLayoutConstraint(item: firstItem!, attribute: firstAttribute!, relatedBy: relation!, toItem: secondItem, attribute: secondAttribute!, multiplier: multiplier!, constant: constant!)
        ret.priority = priority!
        return ret
    }
}

XibLayoutConstraintHelper.swift

//
//  Created by Khanh Le Do on 16/4/16.
//  Copyright © 2016 kloc. All rights reserved.
//

import Foundation
import UIKit

/// If using xib files, it would be not possible to set up the constraints for the view to be located under the Top Guide or above the Bottom Guide. Here we shall provide utility helper to patch the constraints of the view from against Edge to Guide.
public final class XibLayoutConstraintHelper {
    
    // MARK: - Public Methods
    
    public static func patchTopEdgeToTopGuide(viewController: UIViewController) {
        
        let rootView = viewController.view
        
        for constraint in rootView.constraints {
            var constraintBuilder: LayoutConstraintBuilder?

            // Find the Top Edge constraint to the root view & replace it with the Top Guide
            if (constraint.firstItem as? UIView == rootView && constraint.firstAttribute == .Top) {
                constraintBuilder = LayoutConstraintBuilder(origin: constraint)
                    .setFirstItem(viewController.topLayoutGuide)
                    .setFirstAttribute(NSLayoutAttribute.Bottom)
            } else if (constraint.secondItem as? UIView == rootView && constraint.secondAttribute == .Top) {
                constraintBuilder = LayoutConstraintBuilder(origin: constraint)
                    .setSecondItem(viewController.topLayoutGuide)
                    .setSecondAttribute(NSLayoutAttribute.Bottom)
            }
            
            if constraintBuilder != nil {
                // Found it, now we perform the replacement
                rootView.removeConstraint(constraint)
                rootView.addConstraint(constraintBuilder!.build())
            }
        }
    }
    
    // MARK: - Private
}