MessageDisplayable.swift

import UIKit
import Anchorage

protocol MessageDisplayable {
    func configureMessageView(topLayoutGuide: UILayoutSupport)
    func displayMessage(message: String, animated: Bool)
    func hideMessageAnimated(animated: Bool)
}

extension MessageDisplayable where Self: UIViewController {
    var messageLayoutGuide: UILayoutSupport {
        return messageView
    }
    
    func configureMessageView(topLayoutGuide: UILayoutSupport) {
        view.addSubview(messageView)
        
        messageView.topAnchor == topLayoutGuide.bottomAnchor
        messageView.leadingAnchor == view.leadingAnchor
        messageView.trailingAnchor == view.trailingAnchor
    }
    
    func displayMessage(message: String, animated: Bool) {
        messageView.configureWithTitle(message)
        messageView.display(true, animated: animated)
    }
    
    func hideMessageAnimated(animated: Bool) {
        messageView.display(false, animated: animated)
    }
}

// MARK: - Private

private extension MessageDisplayable where Self: UIViewController {
    var messageView: MessageView {
        guard let object = objc_getAssociatedObject(self, &MessageView.associatedKey) as? MessageView else {
            let object = MessageView(frame: .zero)
            objc_setAssociatedObject(self, &MessageView.associatedKey, object, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            
            return object
        }
        
        return object
    }
}

MessageView.swift

import UIKit
import Anchorage

class MessageView: UIView {
    private let titleLabel = UILabel(frame: .zero)
    
    private var heightConstraint: NSLayoutConstraint?
    
    static var associatedKey = "com.bradsmith.messageViewAssociatedKey"
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        backgroundColor = UIColor.messageGreenColor()
        
        configureViews()
        configureLayout()
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

// MARK: - Public

extension MessageView {
    func configureWithTitle(title: String) {
        titleLabel.text = title
    }
    
    func display(display: Bool, animated: Bool) {
        let animations = {
            self.heightConstraint?.active = !display
            self.superview?.layoutIfNeeded()
        }
        
        if animated {
            UIView.animateWithDuration(0.3, animations: animations)
        }
        else {
            animations()
        }
    }
}

// MARK: - Private

private extension MessageView {
    func configureViews() {
        titleLabel.font = UIFont.systemFontOfSize(16.0, weight: UIFontWeightLight)
        titleLabel.textColor = UIColor.whiteColor()
        titleLabel.numberOfLines = 0
        titleLabel.lineBreakMode = .ByWordWrapping
        titleLabel.textAlignment = .Center
        addSubview(titleLabel)
    }
    
    func configureLayout() {
        heightConstraint = heightAnchor == 0.0
        
        titleLabel.verticalAnchors == verticalAnchors + 10.0 ~ UILayoutPriorityDefaultLow
        titleLabel.horizontalAnchors == horizontalAnchors + 10.0 ~ UILayoutPriorityDefaultHigh - 1.0
    }
}

// MARK: - UILayoutSupport

extension MessageView: UILayoutSupport {
    var length: CGFloat {
        return bounds.height
    }
}