Change color plot symbol at index - CorePlot

问题

I try add label of plot symbol when user touch at plot symbol. How to change color this plot symbol,too. Here i my code to add label of plot symbol

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

if(symbolTextAnnotation) {
    [graph.plotAreaFrame.plotArea removeAnnotation:symbolTextAnnotation];
    [symbolTextAnnotation release];
    symbolTextAnnotation = nil;
}
if ([(NSString *)plot.identifier isEqualToString:@"TOTAL"]) {

    // Setup a style for the annotation
    CPTMutableTextStyle *hitAnnotationTextStyle = [CPTMutableTextStyle textStyle];
    hitAnnotationTextStyle.color    = [CPTColor whiteColor];
    hitAnnotationTextStyle.fontSize = 14.0f;
    hitAnnotationTextStyle.fontName = @"SourceSansPro-Bold";

    // Determine point of symbol in plot coordinates
    NSNumber *x          = [[plotData objectAtIndex:index] valueForKey:@"x"];
    NSNumber *y          = [[plotData objectAtIndex:index] valueForKey:@"y"];
    NSArray *anchorPoint = [NSArray arrayWithObjects:x, y, nil];

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

    // Now add the annotation to the plot area
    CPTTextLayer *textLayer = [[[CPTTextLayer alloc] initWithText:[[currencySymbol objectAtIndex:index] stringByAppendingFormat: yString] style:hitAnnotationTextStyle] autorelease];
    symbolTextAnnotation              = [[CPTPlotSpaceAnnotation alloc] initWithPlotSpace:graph.defaultPlotSpace anchorPlotPoint:anchorPoint];
    symbolTextAnnotation.contentLayer = textLayer;
    symbolTextAnnotation.displacement = CGPointMake(0.0f, 20.0f);

    [graph.plotAreaFrame.plotArea addAnnotation:symbolTextAnnotation];

}

回答1:

Implement the -symbolForScatterPlot:recordIndex: method in your datasource. Return a plot symbol for each index that you want to have a special appearance or nil to draw the standard plot symbol (the plotSymbol property) at that index. Call -reloadData on the plot whenever you need to update the plot symbols.

来源：https://stackoverflow.com/questions/13236871/change-color-plot-symbol-at-index-coreplot