Helper (HACK) class to allow the dirty flags on UI elements to be updated when animated using Unity's Legacy system.

LegacyAnimationUI.cs

// <author>Glenn Powell</author>
// <summary>
// Helper (HACK) class to allow the dirty flags on UI elements to be updated when animated using Unity's Legacy system.
// It works by finding all children Animation components of this object, and then individually finding all UI Graphic components under those Animations.
// This allows you to put this behaviour up on a parent object, and have all the animations of it's children UI elements still handled uniquely.
// You could theoretically also put one copy of this component on your Canvas object, and have it handle *all* UI objects, but I haven't personally tried that.
// </summary>

using UnityEngine;
using UnityEngine.UI;
using System.Collections.Generic;

public class LegacyAnimationUI : MonoBehaviour {

	// relationship between Animation components and their UI Graphics
	public class AnimatedGraphic {

		public Animation animation;
		public Graphic[] graphics;

		public AnimatedGraphic(Animation animation, Graphic[] graphics) {
			this.animation = animation;
			this.graphics = graphics;
		}

	}

    // list of relationships
	private List<AnimatedGraphic> m_AnimatedGraphics = new List<AnimatedGraphic>();

	void Awake() {
		// find all legacy animated UI elements
		Animation[] animations = GetComponentsInChildren<Animation>(true);
		foreach (Animation anim in animations) {
			Graphic[] graphics = anim.GetComponentsInChildren<Graphic>(true);

			if (graphics.Length > 0) {
				m_AnimatedGraphics.Add(new AnimatedGraphic(anim, graphics));
			}
		}

		if (m_AnimatedGraphics.Count == 0) {
			Debug.LogWarning("LegacyAnimationUI couldn't find any Legacy Animated UI components in hierarchy object", gameObject);
			enabled = false;
			return;
		}
	}
	
	void Update() {
		// set all dirty flags on any animating graphics
		foreach (AnimatedGraphic animatedGraphic in m_AnimatedGraphics) {
			if (animatedGraphic.animation.isPlaying) {
				foreach (Graphic graphic in animatedGraphic.graphics) {
					graphic.SetAllDirty();

					// NOTE - One of these may be all that's needed to animate color/alpha, but I made this script as simple and general-purpose as possible
					//graphic.SetMaterialDirty();
					//graphic.SetVerticesDirty();
				}
			}
		}
	}

}