Version: 2018.2
public RectTransform fillRect ;

Description

Optional RectTransform to use as fill for the slider.

using UnityEngine;
using System.Collections;
using UnityEngine.UI;  // Required when Using UI elements.

public class Example : MonoBehaviour { public Slider mainSlider; //Reference to new "RectTransform"(Child of FillArea). public RectTransform newFillRect;

//Deactivates the old FillRect and assigns a new one. void Start() { mainSlider.fillRect.gameObject.SetActive(false); mainSlider.fillRect = newFillRect; } }