SubCanvasScaler.cs

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

[ExecuteAlways]
[RequireComponent(typeof(RectTransform))]
public class SubCanvasScaler : MonoBehaviour {
	public enum ScalingMode {
		Stretch,
		MatchHeight,
		MatchWidth,
	}

	public ScalingMode scalingMode = ScalingMode.Stretch;

	RectTransform parent => transform.parent as RectTransform;
	RectTransform rectTransform => transform as RectTransform;

	Vector2 from, to;

	#if UNITY_EDITOR
	void Update(){
		if (!Application.isPlaying)
			LateUpdate();
	}
	#endif

	void LateUpdate(){
		if (from != rectTransform.rect.size || to != parent.rect.size)
			ForceUpdateLayout();
	}

	public void ForceUpdateLayout(){
		rectTransform.pivot = 
		rectTransform.anchorMax = 
		rectTransform.anchorMin = new Vector2(0.5f, 0.5f);

		rectTransform.anchoredPosition = Vector2.zero;

		from = rectTransform.rect.size;
		to = parent.rect.size;

		Vector3 scale = Vector3.one;
		switch (this.scalingMode){
			default:
			case ScalingMode.Stretch: 
					scale.x = to.x / from.x;
					scale.y = to.y / from.y;
				break;

			case ScalingMode.MatchHeight:
				scale.x = 
				scale.y = to.y / from.y;
				break;
			case ScalingMode.MatchWidth:
				scale.y = 
				scale.x = to.x / from.x;
				break;
		}

		rectTransform.localScale = scale;
	}
	
}

SubCanvasScaler.cs.meta

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