[android] Animate margins with ObjectAnimator

MarginProxy.java

import android.view.View;
import android.view.ViewGroup.MarginLayoutParams;

/**
 * Allows an ObjectAnimator to set/get margins of a view
 */
class MarginProxy {
	private View mView;

	public MarginProxy(View view) {
		mView = view;
	}

	public int getLeftMargin() {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		return lp.leftMargin;
	}

	public void setLeftMargin(int margin) {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		lp.setMargins(margin, lp.topMargin, lp.rightMargin, lp.bottomMargin);
		mView.requestLayout();
	}

	public int getTopMargin() {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		return lp.topMargin;
	}

	public void setTopMargin(int margin) {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		lp.setMargins(lp.leftMargin, margin, lp.rightMargin, lp.bottomMargin);
		mView.requestLayout();
	}

	public int getRightMargin() {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		return lp.rightMargin;
	}

	public void setRightMargin(int margin) {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		lp.setMargins(lp.leftMargin, lp.topMargin, margin, lp.bottomMargin);
		mView.requestLayout();
	}

	public int getBottomMargin() {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		return lp.bottomMargin;
	}

	public void setBottomMargin(int margin) {
		MarginLayoutParams lp = (MarginLayoutParams) mView.getLayoutParams();
		lp.setMargins(lp.leftMargin, lp.topMargin, lp.rightMargin, margin);
		mView.requestLayout();
	}
}

MarginProxy.kt

import android.view.View
import android.view.ViewGroup

class MarginProxy(private val view: View) {

    companion object{
        const val LEFT = "left"
        const val TOP = "top"
        const val RIGHT = "right"
        const val BOTTOM = "bottom"
    }

    private val layoutParams by lazy {
        view.layoutParams as ViewGroup.MarginLayoutParams
    }

    fun getMargin(side: String): Int {
        return when (side){
            LEFT -> layoutParams.leftMargin
            TOP -> layoutParams.topMargin
            RIGHT -> layoutParams.rightMargin
            else -> layoutParams.bottomMargin
        }
    }

    fun setMargin(left: Int? = null, top: Int? = null, right: Int? = null, bottom: Int? = null) {
        val leftMargin = left ?: layoutParams.leftMargin
        val topMargin = top ?: layoutParams.topMargin
        val rightMargin = right ?: layoutParams.rightMargin
        val bottomMargin = bottom ?: layoutParams.bottomMargin

        layoutParams.setMargins(leftMargin, topMargin, rightMargin, bottomMargin)
        view.requestLayout()
    }
}