1.定义一个协程LoadNonObjFromAB
 IEnumerator LoadNonObjFromAB(string ABURL, GameObject go, string assetName)

IEnumerator LoadNonObjFromAB(string ABURL, GameObject go, string assetName)
        {
            //参数检查
            if(string.IsNullOrEmpty(ABURL) || go == null)
            {
                Debug.LogError("参数错误！");
            }
            using (WWW www = new WWW(ABURL))
            {
                yield return www;
                AssetBundle ab = www.assetBundle;　　　　//获取AB包
                if(ab != null)
                {
                    if(assetName == "")
                    {
                        go.GetComponent<Renderer>().material.mainTexture = ab.mainAsset as Texture;
                    }
                    else
                    {
                        go.GetComponent<Renderer>().material.mainTexture = (Texture)ab.LoadAsset(assetName);　　//替换贴图为下载的贴图
                        print(assetName);
                    }
                    //卸载AB包
                    ab.Unload(false);
                }
                else
                {
                    Debug.LogError("下载错误："+www.error);
                }
            }
}

2.调用协程

 private void Start()
        {
            StartCoroutine(LoadNonObjFromAB(URL1, testGo, assetName1));
        }

（在调用之前要对参数初始化）