Question

I have the app compiling, but I see no graph.

RaceDetailView.h

#import <UIKit/UIKit.h>
#import "CorePlot-CocoaTouch.h"

@interface RaceDetailView : UIView <CPTPlotDataSource, CPTPlotSpaceDelegate>

@property (nonatomic, retain) NSArray *plotData;
@property (nonatomic, retain) NSString *title;
@property (nonatomic, retain) CPTGraphHostingView *layerHostingView;
@property CGFloat labelRotation;

- (void)setTitleDefaultsForGraph:(CPTGraph *)graph withBounds:(CGRect)bounds;
- (void)setPaddingDefaultsForGraph:(CPTGraph *)graph withBounds:(CGRect)bounds;
-(NSUInteger)numberOfRecords;
-(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index;

@end

RaceDetailView.m

#import "RaceDetailView.h"

@implementation RaceDetailView

@synthesize layerHostingView;
@synthesize labelRotation;
@synthesize title;
@synthesize plotData;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        title = @"my race chart";

        plotData = [[NSMutableArray alloc] initWithObjects:
                    [NSNumber numberWithDouble:20.0],
                    [NSNumber numberWithDouble:30.0],
                    [NSNumber numberWithDouble:60.0],
                    nil];

        CPTGraph *graph = [[[CPTXYGraph alloc] initWithFrame:frame] autorelease];
        //[self addGraph:graph toHostingView:layerHostingView];
        layerHostingView.hostedGraph = graph;
        //[self applyTheme:theme toGraph:graph withDefault:[CPTTheme themeNamed:kCPTDarkGradientTheme]];
        [graph applyTheme:[CPTTheme themeNamed:kCPTDarkGradientTheme]];

        [self setTitleDefaultsForGraph:graph withBounds:frame];
        [self setPaddingDefaultsForGraph:graph withBounds:frame];

        // Setup scatter plot space
        CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)graph.defaultPlotSpace;
        plotSpace.allowsUserInteraction = YES;
        plotSpace.delegate = self;

        // Grid line styles
        CPTMutableLineStyle *majorGridLineStyle = [CPTMutableLineStyle lineStyle];
        majorGridLineStyle.lineWidth = 0.75;
        majorGridLineStyle.lineColor = [[CPTColor colorWithGenericGray:0.2] colorWithAlphaComponent:0.75];

        CPTMutableLineStyle *minorGridLineStyle = [CPTMutableLineStyle lineStyle];
        minorGridLineStyle.lineWidth = 0.25;
        minorGridLineStyle.lineColor = [[CPTColor whiteColor] colorWithAlphaComponent:0.1];    

        CPTMutableLineStyle *redLineStyle = [CPTMutableLineStyle lineStyle];
        redLineStyle.lineWidth = 10.0;
        redLineStyle.lineColor = [[CPTColor redColor] colorWithAlphaComponent:0.5];

        // Axes
        // Label x axis with a fixed interval policy
        CPTXYAxisSet *axisSet = (CPTXYAxisSet *)graph.axisSet;
        CPTXYAxis *x = axisSet.xAxis;
        x.majorIntervalLength = CPTDecimalFromString(@"0.5");
        x.orthogonalCoordinateDecimal = CPTDecimalFromString(@"1.0");
        x.minorTicksPerInterval = 2;
        x.majorGridLineStyle = majorGridLineStyle;
        x.minorGridLineStyle = minorGridLineStyle;

        x.title = @"X Axis";
        x.titleOffset = 30.0;
        x.titleLocation = CPTDecimalFromString(@"1.25");

        // Label y with an automatic label policy. 
        CPTXYAxis *y = axisSet.yAxis;
        y.labelingPolicy = CPTAxisLabelingPolicyAutomatic;
        y.orthogonalCoordinateDecimal = CPTDecimalFromString(@"1.0");
        y.minorTicksPerInterval = 2;
        y.preferredNumberOfMajorTicks = 8;
        y.majorGridLineStyle = majorGridLineStyle;
        y.minorGridLineStyle = minorGridLineStyle;
        y.labelOffset = 10.0;

        y.title = @"Y Axis";
        y.titleOffset = 30.0;
        y.titleLocation = CPTDecimalFromString(@"1.0");

        // Rotate the labels by 45 degrees, just to show it can be done.
        labelRotation = M_PI * 0.25;

        // Set axes
        //graph.axisSet.axes = [NSArray arrayWithObjects:x, y, y2, nil];
        graph.axisSet.axes = [NSArray arrayWithObjects:x, y, nil];

        // Create a plot that uses the data source method
        CPTScatterPlot *dataSourceLinePlot = [[[CPTScatterPlot alloc] init] autorelease];
        dataSourceLinePlot.identifier = @"Data Source Plot";

        CPTMutableLineStyle *lineStyle = [[dataSourceLinePlot.dataLineStyle mutableCopy] autorelease];
        lineStyle.lineWidth = 3.0;
        lineStyle.lineColor = [CPTColor greenColor];
        dataSourceLinePlot.dataLineStyle = lineStyle;

        dataSourceLinePlot.dataSource = self;
        [graph addPlot:dataSourceLinePlot];

        // Auto scale the plot space to fit the plot data
        // Extend the y range by 10% for neatness
        [plotSpace scaleToFitPlots:[NSArray arrayWithObjects:dataSourceLinePlot, nil]];
        CPTPlotRange *xRange = plotSpace.xRange;
        CPTPlotRange *yRange = plotSpace.yRange;
        [xRange expandRangeByFactor:CPTDecimalFromDouble(1.3)];
        [yRange expandRangeByFactor:CPTDecimalFromDouble(1.3)];
        plotSpace.yRange = yRange;

        // Restrict y range to a global range
        CPTPlotRange *globalYRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.0f)
                                                                  length:CPTDecimalFromFloat(2.0f)];
        plotSpace.globalYRange = globalYRange;

        // set the x and y shift to match the new ranges
        CGFloat length = xRange.lengthDouble;
        //xShift = length - 3.0;
        length = yRange.lengthDouble;
        //yShift = length - 2.0;

        // Add plot symbols
        CPTMutableLineStyle *symbolLineStyle = [CPTMutableLineStyle lineStyle];
        symbolLineStyle.lineColor = [CPTColor blackColor];
        CPTPlotSymbol *plotSymbol = [CPTPlotSymbol ellipsePlotSymbol];
        plotSymbol.fill = [CPTFill fillWithColor:[CPTColor blueColor]];
        plotSymbol.lineStyle = symbolLineStyle;
        plotSymbol.size = CGSizeMake(10.0, 10.0);
        dataSourceLinePlot.plotSymbol = plotSymbol;

        // Set plot delegate, to know when symbols have been touched
        // We will display an annotation when a symbol is touched
        dataSourceLinePlot.delegate = self; 
        dataSourceLinePlot.plotSymbolMarginForHitDetection = 5.0f;

        // Add legend
        graph.legend = [CPTLegend legendWithGraph:graph];
        graph.legend.textStyle = x.titleTextStyle;
        graph.legend.fill = [CPTFill fillWithColor:[CPTColor darkGrayColor]];
        graph.legend.borderLineStyle = x.axisLineStyle;
        graph.legend.cornerRadius = 5.0;
        graph.legend.swatchSize = CGSizeMake(25.0, 25.0);
        graph.legendAnchor = CPTRectAnchorBottom;
        graph.legendDisplacement = CGPointMake(0.0, 12.0);
    }
    return self;
}

- (void)setTitleDefaultsForGraph:(CPTGraph *)graph withBounds:(CGRect)bounds
{
    graph.title = title;
    CPTMutableTextStyle *textStyle = [CPTMutableTextStyle textStyle];
    textStyle.color = [CPTColor grayColor];
    textStyle.fontName = @"Helvetica-Bold";
    textStyle.fontSize = round(bounds.size.height / 20.0f);
    graph.titleTextStyle = textStyle;
    graph.titleDisplacement = CGPointMake(0.0f, round(bounds.size.height / 18.0f)); // Ensure that title displacement falls on an integral pixel
    graph.titlePlotAreaFrameAnchor = CPTRectAnchorTop;    
}

- (void)setPaddingDefaultsForGraph:(CPTGraph *)graph withBounds:(CGRect)bounds
{
    float boundsPadding = round(bounds.size.width / 20.0f); // Ensure that padding falls on an integral pixel
    graph.paddingLeft = boundsPadding;

    if (graph.titleDisplacement.y > 0.0) {
        graph.paddingTop = graph.titleDisplacement.y * 2;
    }
    else {
        graph.paddingTop = boundsPadding;
    }

    graph.paddingRight = boundsPadding;
    graph.paddingBottom = boundsPadding;    
}

-(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plot
{
    return [plotData count];
}

-(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index
{
    NSNumber *num;
    if (fieldEnum == CPTPieChartFieldSliceWidth) {
        num = [plotData objectAtIndex:index];
    }
    else {
        return [NSNumber numberWithInt:index];
    }

    return num;
}

@end

Edit: You may note that this is from the CorePlot example SimpleScatterPlot.

Answer 1

Why is this code in a UIView? This code normally resides in a view controller (UIViewController). The Plot Gallery app that you pulled the example from is a little more complicated because it uses the plots in multiple places–in the main view area and also to make the thumbnail images for the list or browser view.

Do you ever set the layerHostingView? Is it in the view hierarchy and visible?

Check your datasource as @danielbeard suggested. The correct field names for scatter plots are CPTScatterPlotFieldX and CPTScatterPlotFieldY.