code: def get_next_step(self):
          
          if is_raster_layer(self.parent.layer):
              new_step = self.parent.step_kw_band_selector
          else:
              new_step = self.parent.step_kw_layermode
          return new_step
docs: Find the proper step when user clicks the Next button.
  
          :returns: The step to be switched to
          :rtype: WizardStep instance or None