Custom Tab Bar

CustomTabBar.swift

//
//  CustomTabBar.swift
//  welbe
//
//  Created by Ben Norris on 12/8/15.
//  Copyright © 2015 O.C. Tanner Corporation. All rights reserved.
//

import UIKit

protocol CustomTabBarDelegate {
    func tabBar(tabBar: CustomTabBar, didSelectTab tab: Int)
}

@IBDesignable class CustomTabBar: UIView {

    // MARK: - Inspectable properties
    
    @IBInspectable var underlineHeight: CGFloat = 2.0 {
        didSet {
            underlineHeightConstraint?.constant = underlineHeight
        }
    }
    
    @IBInspectable var underlineOnBottom: Bool = true {
        didSet {
            configureUnderlineVerticalPosition()
        }
    }
    
    @IBInspectable var selectedIndex: Int = 0 {
        didSet {
            updateButtons()
        }
    }
    
    @IBInspectable var accentColor: UIColor = UIColor.blueColor() {
        didSet {
            updateColors()
        }
    }
    
    @IBInspectable var defaultTitleColor: UIColor = UIColor.blackColor() {
        didSet {
            updateColors()
        }
    }
    
    
    // MARK: - Exposed properties
    
    var titles: [String] = ["one", "two"] {
        didSet {
            configureButtons()
        }
    }
    var delegate: CustomTabBarDelegate?
    
    
    // MARK: - Private properties
    
    private let stackView = UIStackView()
    private var buttons = [UIButton]()
    
    private let underline = UIView()
    private var underlineHeightConstraint: NSLayoutConstraint?
    private var underlineWidthConstraint: NSLayoutConstraint?
    private var underlinePositionContraint: NSLayoutConstraint?
    private var underlineTopConstraint: NSLayoutConstraint?
    private var underlineBottomConstraint: NSLayoutConstraint?
    
    
    // MARK: - Method overrides
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupViews()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupViews()
    }
    
    
    // MARK: - Exposed API
    
    func tabSelected(button: UIButton) {
        guard let index = buttons.indexOf(button) else { fatalError("Invalid button selected") }
        selectedIndex = index
        delegate?.tabBar(self, didSelectTab: index)
    }
    
}


// MARK: - Private methods

private extension CustomTabBar {
    
    func setupViews() {
        stackView.translatesAutoresizingMaskIntoConstraints = false
        stackView.distribution = .FillEqually
        addSubview(stackView)
        stackView.leadingAnchor.constraintEqualToAnchor(leadingAnchor).active = true
        stackView.topAnchor.constraintEqualToAnchor(topAnchor).active = true
        stackView.trailingAnchor.constraintEqualToAnchor(trailingAnchor).active = true
        stackView.bottomAnchor.constraintEqualToAnchor(bottomAnchor).active = true
        
        underline.translatesAutoresizingMaskIntoConstraints = false
        addSubview(underline)
        underlineBottomConstraint = underline.bottomAnchor.constraintEqualToAnchor(bottomAnchor)
        underlineBottomConstraint?.active = true
        underlineTopConstraint = underline.topAnchor.constraintEqualToAnchor(topAnchor)
        underlineHeightConstraint = underline.heightAnchor.constraintEqualToConstant(underlineHeight)
        underlineHeightConstraint?.active = true
        underlinePositionContraint = underline.leadingAnchor.constraintEqualToAnchor(leadingAnchor)
        underlinePositionContraint?.active = true
        
        configureButtons()
        configureUnderlineVerticalPosition()
        updateColors()
        if selectedIndex < buttons.count {
            let button = buttons[selectedIndex]
            tabSelected(button)
        }
    }
    
    func configureButtons() {
        for button in buttons {
            button.removeFromSuperview()
        }
        buttons.removeAll()
        
        for title in titles {
            createButton(title)
        }
        configureUnderlineWidth()
        
        if !(selectedIndex < buttons.count) {
            fatalError("Invalid selection for buttons: \(selectedIndex)")
        }
        let selectedButton = buttons[selectedIndex]
        tabSelected(selectedButton)
    }
    
    func createButton(title: String?) {
        let button = UIButton(type: .System)
        button.setTitle(title, forState: .Normal)
        button.setTitleColor(defaultTitleColor, forState: .Normal)
        button.titleLabel?.font = UIFont.appFont(17.0)
        button.addTarget(self, action: "tabSelected:", forControlEvents: .TouchUpInside)
        stackView.addArrangedSubview(button)
        buttons.append(button)
    }
    
    func configureUnderlineWidth() {
        underlineWidthConstraint = underline.widthAnchor.constraintEqualToAnchor(widthAnchor, multiplier: 1 / CGFloat(titles.count))
        underlineWidthConstraint?.active = true
    }
    
    func configureUnderlineVerticalPosition() {
        if underlineOnBottom {
            underlineBottomConstraint?.active = true
            underlineTopConstraint?.active = false
        } else {
            underlineBottomConstraint?.active = false
            underlineTopConstraint?.active = true
        }
    }
    
    func updateColors() {
        underline.backgroundColor = accentColor
        for button in buttons {
            button.setTitleColor(defaultTitleColor, forState: .Normal)
            button.setTitleColor(accentColor, forState: .Highlighted)
        }
    }
    
    func updateButtons() {
        if !(selectedIndex < buttons.count) {
            fatalError("Invalid index for buttons—selectedIndex: \(selectedIndex)")
        }
        for button in buttons {
            button.setTitleColor(defaultTitleColor, forState: .Normal)
        }
        let currentSelection = buttons[selectedIndex]
        currentSelection.setTitleColor(accentColor, forState: .Normal)
        
        // TODO: Add animation
        let position = frame.size.width / CGFloat(titles.count) * CGFloat(selectedIndex)
        self.underlinePositionContraint?.constant = position
        UIView.animateWithDuration(0.3, delay: 0.0, usingSpringWithDamping: 0.7, initialSpringVelocity: 1.0, options: [], animations: { () -> Void in
            self.layoutIfNeeded()
            }, completion: nil)
    }
    
}