Question

I am trying to change to core plot’s majorIntervalScale while I’m zooming so as less items appear on the axis when zooming out and more appear when zooming in. I can’t get this to work can anyone help please? Here’s the code that I got so far. Thanks

-(BOOL)plotSpace:(CPTPlotSpace *)space shouldScaleBy:(CGFloat)interactionScale aboutPoint:(CGPoint)interactionPoint
{
    return YES;
}

-(CPTPlotRange *)plotSpace:(CPTPlotSpace *)space willChangePlotRangeTo:(CPTPlotRange *)newRange forCoordinate:(CPTCoordinate)coordinate
{
    self.graphScaleX = self.graphScaleX*newRange.lengthDouble;
    self.graphScaleY = self.graphScaleY*newRange.lengthDouble;

    CPTXYAxisSet *axisSet = (CPTXYAxisSet *)self.graph.axisSet;
    CPTXYAxis *x          = axisSet.xAxis;

    CPTXYAxis *y          = axisSet.yAxis;

    x.majorIntervalLength=CPTDecimalFromFloat(self.graphScaleX);
    y.majorIntervalLength=CPTDecimalFromFloat(self.graphScaleY);

    return newRange;
}

Answer 1

It looks like you always want to have the same number of tick marks no matter the length of the plot range. If so, use a different axis labeling policy instead of a delegate. The CPTAxisLabelingPolicyAutomatic policy will find tick marks on “nice” numbers, but not necessarily the ends of the plot range. The CPTAxisLabelingPolicyEqualDivisions will place equally-spaced ticks starting at one end of the plot range and continuing to the other. Both of these labeling policies use the preferredNumberOfMajorTicks to control how many tick marks to draw.