Overloads the calculate values method to calculate the values for
        this axis based on the minimum and maximum values, and the number
        of steps desired.
        
        :return     [<variant>, ..]

def calculateValues(self):
        """
        Overloads the calculate values method to calculate the values for
        this axis based on the minimum and maximum values, and the number
        of steps desired.
        
        :return     [<variant>, ..]
        """
        chart = self.chart()
        if not chart:
            return super(XDatasetAxis, self).calculateValues()
        else:
            values = []
            for dataset in chart.datasets():
                values.append(dataset.name())
            values.sort()
            return values