code: def update_channels(self):
          
          if not self.gui_up:
              return
  
          self.logger.debug("channel configuration has changed--updating gui")
          try:
              channel = self.fv.get_channel(self.chname)
  
          except KeyError:
              channel = self.fv.get_channel_info()
  
          if channel is None:
              raise ValueError('No channel available')
  
          self.chname = channel.name
  
          w = self.w.channel_name
          w.clear()
  
          self.chnames = list(self.fv.get_channel_names())
          #self.chnames.sort()
          for chname in self.chnames:
              w.append_text(chname)
  
          # select the channel that is the current one
          try:
              i = self.chnames.index(channel.name)
          except IndexError:
              i = 0
          self.w.channel_name.set_index(i)
  
          # update the image listing
          self.redo()
docs: Update the GUI to reflect channels and image listing.