dp转px,px转dp, kotlin 扩展方法，不需要cont

val Float.px
    get() = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PX,this, Resources.getSystem().displayMetrics)

val Float.dp
    get() = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,this, Resources.getSystem().displayMetrics)

val Float.sp
    get() = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP,this, Resources.getSystem().displayMetrics)

val Int.dp
    get() = this.toFloat().dp