Resources.UnloadUnusedAssets doesn't work as expected

Unity Engine
,
1

// Resources.UnloadUnusedAssets doesn’t work in Coroutine.

using System;
using System.Collections;
using UnityEditor;
using UnityEngine;

public class TestMaterialUnload : MonoBehaviour
{
    private Renderer renderer1;
    private Action action;
    void Start()
    {
        renderer1 = GameObject.CreatePrimitive(PrimitiveType.Cube).GetComponent<Renderer>();

        UnLoad();
        UnLoadImmediate();
        StartCoroutine(UnLoadCoroutine());
    }

    void Update()
    {
        action?.Invoke();
    }
   
    private void UnLoad()
    {
        var material = Material.Instantiate(renderer1.sharedMaterial);
        Debug.Log("UnLoad Before: " + material); // Standard(Clone) (UnityEngine.Material)
        var a = Resources.UnloadUnusedAssets();

        a.completed += (op) =>
        {
            Debug.Log("UnLoad After: " + material); // null
        };
    }
   
    private IEnumerator UnLoadCoroutine()
    {
        var material = Material.Instantiate(renderer1.sharedMaterial);
        Debug.Log("UnLoadCoroutine Before: " + material); // Standard(Clone) (UnityEngine.Material)
        var a = Resources.UnloadUnusedAssets();

        a.completed += (op) =>
        {
            Debug.Log("UnLoadCoroutine After completed: " + material); // Standard(Clone) (UnityEngine.Material)
        };
       
        while (!a.isDone)
        {
            yield return null;
        }

        Debug.LogWarning("UnLoadCoroutine After: " + material); // Standard(Clone) (UnityEngine.Material)

        action = () => { Debug.LogWarning("UnLoadCoroutine action: " + material); }; // Standard(Clone) (UnityEngine.Material)

        action();
    }
   
    private void UnLoadImmediate()
    {
        var material = Material.Instantiate(renderer1.sharedMaterial);
        Debug.Log("UnLoadImmediate3 Before: " + material); // Standard(Clone) (UnityEngine.Material)
        EditorUtility.UnloadUnusedAssetsImmediate();
        Debug.Log("UnLoadImmediate3 After: " + material); // null
    }
   
   
}
2

I am not sure what exactly your question is, but if you want to wait for Resources.UnloadUnusedAssets to complete in a Coroutine, you could try this:

private IEnumerator UnLoadCoroutine()
    {
        var material = Material.Instantiate(renderer1.sharedMaterial);
        Debug.Log("UnLoadCoroutine Before: " + material); // Standard(Clone) (UnityEngine.Material)
        yield return Resources.UnloadUnusedAssets();

        Debug.Log("UnLoadCoroutine After completed: " + material);

        action();
    }