def count_channels(self):
        """If more than one channel selected, activate merge checkbox."""
        merge = self.index['merge']

        if len(self.idx_chan.selectedItems()) > 1:
            if merge.isEnabled():
                return
            else:
                merge.setEnabled(True)
        else:
            self.index['merge'].setCheckState(Qt.Unchecked)
            self.index['merge'].setEnabled(False)