问核心图iOS从CPTPlotSpace点的数据中获取点

EN

-(void)scatterPlot:(CPTScatterPlot *)plot plotSymbolWasSelectedAtRecordIndex:(NSUInteger)index{

CPTXYGraph *graph = (self.graphs)[0];

if ( symbolTextAnnotation ) {
    [graph.plotAreaFrame.plotArea removeAnnotation:symbolTextAnnotation];
    symbolTextAnnotation = nil;
}

// Setup a style for the annotation
CPTMutableTextStyle *hitAnnotationTextStyle = [CPTMutableTextStyle textStyle];
hitAnnotationTextStyle.color    = [CPTColor whiteColor];
hitAnnotationTextStyle.fontSize = 16.0;
hitAnnotationTextStyle.fontName = @"Helvetica-Bold";

// Determine point of symbol in plot coordinates
NSDictionary *dataPoint = plotData[index];

NSNumber *x = dataPoint[@(CPTScatterPlotFieldX)];
NSNumber *y = dataPoint[@(CPTScatterPlotFieldY)];

NSArray *anchorPoint = @[x, y];

// Add annotation
// First make a string for the y value
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:2];
NSString *yString = [formatter stringFromNumber:y];

// Now add the annotation to the plot area
CPTTextLayer *textLayer = [[CPTTextLayer alloc] initWithText:yString style:hitAnnotationTextStyle] ;


CPTImage *background = [CPTImage imageForPNGFile:@"check"];
textLayer.fill          = [CPTFill fillWithImage:background];
textLayer.paddingLeft   = 2.0;
textLayer.paddingTop    = 2.0;
textLayer.paddingRight  = 2.0;
textLayer.paddingBottom = 2.0;

symbolTextAnnotation                    = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:graph.defaultPlotSpace anchorPlotPoint:anchorPoint];
symbolTextAnnotation.contentLayer       = textLayer;
symbolTextAnnotation.contentAnchorPoint = CGPointMake(0.5, 0.0);
symbolTextAnnotation.displacement       = CGPointMake(0.0, 10.0);
[graph.plotAreaFrame.plotArea addAnnotation:symbolTextAnnotation];
}