GLib: in GIO, GFileAttribute namespace "thumbnail" and "preview" doesn't work

[steven hooke <stevenhooke11 gmail com>]

I wrote a test program here.

-----------------------------------

GFile* file = g_file_new_for_path (file_name); //filename is read from 

    GError* error=NULL;

    GFileInfo *info = g_file_query_info(file, "standard::*,thumbnail::*,preview::*", 

                                            G_FILE_QUERY_INFO_NONE, NULL, &error);

    if (error!=NULL)

    {

        g_print("get_icon error: %s\n", error->message);

    }

    if (info != NULL)

    {

        gboolean b1=g_file_info_has_namespace(info, "standard");

gboolean b2=g_file_info_has_namespace(info, "thumbnail");

        gboolean b3=g_file_info_has_namespace(info, "preview");

    }

--------------------------------------

Result:

b1 = 1,

b2 = 0,

b3 = 0.

So my question is how to enable "thumbnail" and "preview" namespace(or how to use "thumbnail" and "preview").