Objective c 我如何画垂直线？

如何为每个日期画一条垂直线

y轴工作正常，但为什么x轴不行

x轴的代码：

CPTMutableLineStyle *majorGridLineStyle = [CPTMutableLineStyle lineStyle];
majorGridLineStyle.lineWidth = 2;
majorGridLineStyle.lineColor = [CPTColor redColor];

CPTXYAxisSet *axisSet = (CPTXYAxisSet *)graph.axisSet;

CPTXYAxis *x = [axisSet xAxis];
x.axisLineStyle = nil;
x.majorTickLineStyle = majorGridLineStyle;

[x setLabelingPolicy:CPTAxisLabelingPolicyNone];
x.majorGridLineStyle = majorGridLineStyle;

NSArray *subjectsArray = [self getSubjectTitlesAsArray];
[x setAxisLabels:[NSSet setWithArray:subjectsArray]];

y轴的代码：

CPTXYAxis *y = axisSet.yAxis;
y.axisLineStyle = nil;
y.majorTickLineStyle = nil;
y.minorTickLineStyle = nil;
y.majorIntervalLength = CPTDecimalFromString(@"500");
y.orthogonalCoordinateDecimal = CPTDecimalFromString(@"0");

y.majorGridLineStyle = gridLineStyle;

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我的错误是什么？

核心图将在主要刻度位置绘制网格线。确保日期值与勾号位置相对应，并且

gridLineStyle

是在白色背景下显示的样式。

谢谢Eric

当然，还有一些更优雅的编码方法，但我是这样解决的：

    NSMutableSet *xMajorLocations = [NSMutableSet set];
[xMajorLocations addObject:[NSNumber numberWithFloat:0.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:1.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:2.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:3.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:4.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:5.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:6.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:7.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:8.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:9.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:10.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:11.0f]];
[xMajorLocations addObject:[NSNumber numberWithFloat:12.0f]];

x.majorTickLocations = xMajorLocations;