核心图注释坐标返回 null

Question

我有一个工作核心图，这是我的第一个，目前正在尝试实现注释。我已记录注释以及 x 和 y 坐标，它们为空。谢谢

-(void)scatterPlot:(CPTScatterPlot *)plot plotSymbolWasSelectedAtRecordIndex:(NSUInteger)index
{
    //CPTGraph* graph = [graphs objectAtIndex:0];

    NSLog(@"add annotation called");

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

    // Setup a style for the annotation
    CPTMutableTextStyle *hitAnnotationTextStyle = [CPTMutableTextStyle textStyle];
    hitAnnotationTextStyle.color = [CPTColor whiteColor];
    hitAnnotationTextStyle.fontSize = 16.0f;
    hitAnnotationTextStyle.fontName = @"Helvetica-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];
    NSLog(@"x %@, y %@",[[plotData objectAtIndex:index] valueForKey:@"x"],y);

    // 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: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];   
    //[graph addAnnotation:symbolTextAnnotation];

    CPTAnnotation *annot = [graph.plotAreaFrame.plotArea.annotations objectAtIndex:0];
    NSLog(@"annot: %@", annot);
}

Answer 1

这是确定锚点的代码：

NSNumber *x = [[plotData objectAtIndex:index] valueForKey:@"x"];
NSNumber *y = [[plotData objectAtIndex:index] valueForKey:@"y"];
NSArray *anchorPoint = [NSArray arrayWithObjects:x, y, nil];

它假设您的绘图数据作为 NSNumber 对象存储在带有“x”和“y”键的字典数组中。如果您的数据以其他方式存储，您将必须以不同的方式提取值。重要的是将两个数字打包在 NSArray 中，首先是 x 值，然后是 y 值。