Measuring Width/Height.

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        val defaultWidth = getDefaultSize(suggestedMinimumWidth, widthMeasureSpec)
        val defaultHeight = getDefaultSize(suggestedMinimumHeight, heightMeasureSpec)
        setMeasuredDimension(defaultWidth, defaultHeight)
        // 여기서부터 measuredWidth / measuredHeight의 올바른 사용이 가능해진다.
    }