Xadmin List_display中显示缩略图

#-*- coding: UTF-8 -*- 
from django.db import models
from django.contrib.auth.models import User
from django.utils.translation import ugettext as _
from userena.models import UserenaBaseProfile

class MyProfile(UserenaBaseProfile):
    user = models.OneToOneField(User,unique=True,verbose_name=_('user'),related_name='my_profile')
    one_card=models.FileField(u'一卡通',null=True,blank=True,upload_to='onecard')

#########################关键是如下函数
    def image_img(self):
        if self.one_card:
            return str('<img src="%s" />' % self.one_card.url)
        else:
            return u'上传头像'
    image_img.short_description = '头像'
    image_img.allow_tags = True

#-*- coding: UTF-8 -*- 

# Register your models here.
import xadmin

from models import MyProfile

class MyProfileAdmin(object):
    list_display = ('user','favourite_snack','image_img')
    list_display_links = ('user','image_img')

xadmin.site.register(MyProfile,MyProfileAdmin)

#-*- coding: UTF-8 -*- 
from django.db import models
from django.contrib.auth.models import User
from django.utils.translation import ugettext as _
from userena.models import UserenaBaseProfile

#########################关键StdImageField(）
class MyProfile(UserenaBaseProfile):
    user = models.OneToOneField(User,unique=True,verbose_name=_('user'),related_name='my_profile')
    one_card=StdImageField(upload_to='onecard', variations={'thumbnail': (100, 75)}) # creates a thumbnail resized to maximum size to fit a 100x75 area

#########################关键self.one_card.thumbnail.url
    def image_img(self):
        if self.one_card:
            return str('<img src="%s" />' % self.one_card.thumbnail.url)
        else:
            return u'上传头像'
    image_img.short_description = '头像'
    image_img.allow_tags = True