UnityWebRequest 本地加载图片

string filePath = Application.streamingAssetsPath + "/证书/a4证书"+ str+".png";
print(filePath);

IEnumerator GetTexture(string url) {
        UnityWebRequest uwr = UnityWebRequest.Get(url);
        DownloadHandlerTexture downloadTexture = new DownloadHandlerTexture(true);
        uwr.downloadHandler = downloadTexture;
        yield return uwr.SendWebRequest();
        if (uwr.isNetworkError || uwr.isHttpError) {
            print(uwr.error);
        } else {
            Texture2D t = downloadTexture.texture;
            showPic.sprite = Sprite.Create(t, new Rect(0, 0, t.width, t.height), Vector2.one);
        }
    }