如何处理从网上下载文件后导入资产的问题?

有没有办法避免这种情况,或者等到它完成后再加载文件?我正在为iOS开发

下面是下载和加载.obj文件的代码:

IEnumerator DownloadAndLoadFile(string url) { 

var uwr = new UnityWebRequest(url, UnityWebRequest.kHttpVerbGET);
string modelSavePath = Path.Combine(Application.dataPath, "Resources");
modelSavePath = Path.Combine(modelSavePath, docName); 

    if (!Directory.Exists(Path.GetDirectoryName(modelSavePath)))
    {
        Directory.CreateDirectory(Path.GetDirectoryName(modelSavePath));
    }

 var dh = new DownloadHandlerFile(modelSavePath);
 dh.removeFileOnAbort = true; 
 uwr.downloadHandler = dh;  

AsyncOperation request = uwr.SendWebRequest();
while (!request.isDone)
    { 
        Debug.Log("Progress: " + request.progress);
        yield return null;
    }  
 if(request.isDone){

     Debug.Log("File successfully downloaded and saved to " + modelSavePath);
          // Load Main scene
        Scene s = SceneManager.GetSceneByName("Main");
        if (s.isLoaded) {
                         var allObjects = Resources.FindObjectsOfTypeAll<MainAssetSwitch>(); 
                            if (allObjects.Length > 0) { 
                                var targetobject = allObjects [0];   
                                 targetobject.SetActive(true);
                                 Object prefabReference = Resources.Load(docName);
                                  GameObject gameObjectReference = Instantiate(prefabReference) as GameObject;
                                  ameObjectReference.transform.parent = targetobject.transform; 
                            } 
            }


 }

if (uwr.isNetworkError || uwr.isHttpError)
    {Debug.LogError(uwr.error);}

}

下面是Unity在我加载从internet下载的.obj文件后将自动运行的内容。

我还收到一个错误,说“ArgumentException:您要实例化的对象为null”,因为下载过程完成后,资产没有导入到资源文件中。