two x axes in the same graph?

How to dra开发者_如何学运维w two x axes in the same graph when drawing with core-plot?

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 CPXYAxis *topX = [[[CPXYAxis alloc] init] autorelease];
 CPXYAxis *bottomX = [[[CPXYAxis alloc] init] autorelease];
 CPXYAxis *y = [[[CPXYAxis alloc] init] autorelease];

 topX.coordinate = CPCoordinateX;
 bottomX.coordinate = CPCoordinateX;

 y.coordinate = CPCoordinateY;

 CPAxisSet *axisSet = [[[CPAxisSet alloc] init] autorelease];
 axisSet.axes = [NSArray arrayWithObjects:topX,bottomX,y,nil];
 graph.axisSet = axisSet;

You might need multiple plot spaces, each of on x axis..CPTestApp example creates multiple y axis, which will help you..Hope this helps..