u3d外部资源 打包与加载的问题

[MenuItem("Custom Editor/Build AssetBundle From Selection Twice")]
static void ExportResourceNoTrack()
{
    // Bring up save panel
    string path = EditorUtility.SaveFilePanel("Save Resource", "", "New Resource", "unity3d");
    if (path.Length != 0)
    {
        // Build the resource file from the active selection.
        BuildPipeline.BuildAssetBundle(Selection.activeObject, Selection.objects, path);
    }
}

TextAsset txt = m_Download.assetBundle.Load(filename, typeof(TextAsset)) as TextAsset;