Animation only works on one button (ripple view)

问题

Site used: https://material.io/develop/ios/components/ripple/

Here is my code:

import MaterialComponents.MaterialRipple

class ViewController: UIViewController {

//    let rippleView = MDCRippleView()
    let rippleTouchController = MDCRippleTouchController()

    @IBOutlet weak var playBtn: UIButton!
    @IBOutlet weak var levelsBtn: UIButton!
    @IBOutlet weak var topicsBtn: UIButton!
    @IBOutlet weak var settingsBtn: UIButton!
    @IBOutlet weak var instaBtn: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()

        //This works for instabtn (lastone)
        //        rippleTouchController.rippleView.rippleColor = .lightGray
        //        rippleTouchController.addRipple(to: playBtn)
        //        rippleTouchController.addRipple(to: levelsBtn)
        //        rippleTouchController.addRipple(to: topicsBtn)
        //        rippleTouchController.addRipple(to: settingsBtn)
        //        rippleTouchController.addRipple(to: instaBtn)

    }


    override func viewDidAppear(_ animated: Bool) {

        // Currently only works for playbtn
        rippleTouchController.rippleView.rippleColor = .lightGray
        rippleTouchController.addRipple(to: levelsBtn)
        rippleTouchController.addRipple(to: topicsBtn)
        rippleTouchController.addRipple(to: settingsBtn)
        rippleTouchController.addRipple(to: instaBtn)
        rippleTouchController.addRipple(to: playBtn)
    }
}

I've tried to put the code in viewDidAppear but it doesn't make a difference. Any thoughts?

来源：https://stackoverflow.com/questions/59721788/animation-only-works-on-one-button-ripple-view