override fun initAnimation() {
        val btns = arrayOf(btn1, btn2, btn3)
        val labels = arrayOf(btn1Label, btn2Label, btn3Label)

        for (i in 0 until btns.size) {
            val btn = btns[i]
            val startWidth = context!!.dip(50)
            endWidth = btn.width
            val params = btn.layoutParams
            params.width = startWidth
            btn.layoutParams = params

            val label = labels[i]
            label.alpha = 0f
        }
    }

    override fun startAnimation() {
        val btns = arrayOf(btn1, btn2, btn3)
        val labels = arrayOf(btn1Label, btn2Label, btn3Label)

        for (i in 0 until btns.size) {
            val btn = btns[i]
            val startWidth = context!!.dip(50)

            val animator = ValueAnimator.ofInt(startWidth, endWidth)
            animator.startDelay = 100 + i * 50L
            animator.duration = 300
            animator.interpolator = AccelerateDecelerateInterpolator()
            animator.addUpdateListener { animation ->
                btn.layoutParams.width = animation.animatedValue as Int
                btn.requestLayout()
            }
            animator.start()

            val label = labels[i]
            label.animate()
                    .alpha(1f)
                    .setDuration(200)
                    .setStartDelay(200 + i * 50L)
                    .start()
        }
    }