UnderlineAnimator

MDVUnderlineAnimator.swift

import UIKit

public class MDVUnderlineAnimator: MDVTabBarAnimatable {
    
    private var underlineColor: UIColor = .clear
    private var underlineHeight: CGFloat = 0
    private var xPosition: CGFloat = 0
    private var yPositionOffset: CGFloat = 0
    private var containerWidth: CGFloat = 0
    private var underlineView: UIView = UIView(frame: .zero)
    
    private let duration: Double
    private let delay: Double
    private let damping: CGFloat
    private let velocity: CGFloat
    
    
    public init(withUnderlineColor underlineColor: UIColor = .red,
         underlineHeight: CGFloat = 8,
         yPositionOffset: CGFloat = 0,
         duration: Double = 0.3,
         delay: Double = 0,
         damping: CGFloat = 0.5,
         velocity: CGFloat = 0.6){
        self.underlineColor = underlineColor
        self.underlineHeight = underlineHeight
        self.yPositionOffset = yPositionOffset
        
        self.damping = damping
        self.duration = duration
        self.delay = delay
        self.velocity = velocity
    }
    
    public func prepareForAnimation(onMDVTabBar tabBar: UIView, withContainers containers: [MDVTabBarContainer], andInitialIndex initialIndex: Int) {
        xPosition = CGFloat(containers[initialIndex].frame.origin.x)
        let yPosition = CGFloat(tabBar.frame.height - underlineHeight)
        containerWidth = containers[initialIndex].frame.width
        self.underlineView = UIView(frame: CGRect(x: xPosition,
                                                  y: yPosition,
                                                  width: containerWidth,
                                                  height: self.underlineHeight))
        self.underlineView.backgroundColor = self.underlineColor
        tabBar.insertSubview(self.underlineView, at: 0)
    }
    
    public func performAnimation(fromIndex: Int,
                          toIndex: Int,
                          onMDVTabBar tabBar: UIView,
                          withContainers containers: [MDVTabBarContainer],
                          completion: @escaping () -> Void) {
        
        UIView.animate(withDuration: duration,
                       delay: delay,
                       usingSpringWithDamping: damping,
                       initialSpringVelocity: velocity,
                       options: .curveLinear,
                       animations: {
                        self.xPosition = CGFloat(containers[toIndex].frame.origin.x)
                        self.underlineView.frame.origin.x = self.xPosition
                        completion()
        })
    }
}