subscriber in rqt plugin python

edit

I'm writing a rqt plugin in python, but can't get the subscriber to work. I want the string from "controller/mode" to show in "lineControlMode". For some reason this doesn't happen. Hope some of you can help me.

import os
import rospkg
import rospy

from qt_gui.plugin import Plugin
from python_qt_binding import loadUi
from python_qt_binding.QtWidgets import QWidget, QGraphicsView
from std_msgs.msg import String

class MyPlugin(Plugin):

def __init__(self, context):
    #PLUGIN CODE
    super(MyPlugin, self).__init__(context)

    # Give QObjects reasonable names
    self.setObjectName('MyPlugin')
    rp = rospkg.RosPack()

    # Process standalone plugin command-line arguments
    from argparse import ArgumentParser
    parser = ArgumentParser()
    # Add argument(s) to the parser.
    parser.add_argument("-q", "--quiet", action="store_true",
                  dest="quiet",
                  help="Put plugin in silent mode")
    args, unknowns = parser.parse_known_args(context.argv())
    if not args.quiet:
        print 'arguments: ', args
        print 'unknowns: ', unknowns

    # Create QWidget
    self._widget = QWidget()
    ui_file = os.path.join(rp.get_path('rqt_vortex_control_mode'), 'resource', 'MyPlugin.ui')

    # Extend the widget with all attributes and children from UI file
    loadUi(ui_file, self._widget)

    # Give QObjects reasonable names
    self._widget.setObjectName('MyPluginUi')

    # Add widget to the user interface
    context.add_widget(self._widget)

    #MY CODE
    self._widget.lineControlMode.setReadOnly(True)
    self._widget.lineControlMode.setText("init")

    #Subscriber
    self.sub = rospy.Subscriber("/uranus_dp/controller/mode", String, self.callback)

def shutdown_plugin(self):
    self.sub.unregister()

def callback(self, mode):
    self._widget.lineControlMode.setText(mode)

Here is the link to my repository just in case: https://github.com/vortexntnu/rov-gui