x轴上带有月份的核心图（iphone）

Question

我想在 iphone 上使用 coreplot 绘制一个 XY 图，x 轴为日期，y 轴为一些值。参考与 coreplot SDK 一起提供的 DatePlot 示例，我能够在 x 轴上按月绘制带有日期的图表（即 x 范围从一个月的 1 个日期到最后一个日期）。现在我想要一个年度规模，即我想在 x 轴上显示所有月份名称（Jan、Feb、Mar 等），并将我的刻度间隔显示为一个月时间。

我使用以下代码来显示每月的值

oneXUnit        =   60 * 60 * 24;
x.majorIntervalLength    =  CPDecimalFromFloat((float) oneXUnit);
NSDateFormatter *dateFormatter   =   [[[NSDateFormatter alloc] init]autorelease];
NSString *dateString        =   @"0";
[dateFormatter setDateFormat:@"MM"];
CPTimeFormatter *timeFormatter  =   [[CPTimeFormatter alloc]initWithDateFormatter:dateFormatter];
timeFormatter.referenceDate =   [dateFormatter dateFromString:dateString];
x.labelFormatter    =   timeFormatter;

现在对于年度模式，x 刻度间隔需要为一个月。我尝试了下面的代码，但没有工作

oneXUnit        =   60 * 60 * 24 * 30;
x.majorIntervalLength    =  CPDecimalFromFloat((float) oneXUnit);
NSDateFormatter *dateFormatter   =   [[[NSDateFormatter alloc] init]autorelease];
NSString *dateString        =   @"Jan";
[dateFormatter setDateFormat:@"MMM"];
CPTimeFormatter *timeFormatter  =   [[CPTimeFormatter alloc]initWithDateFormatter:dateFormatter];
timeFormatter.referenceDate =   [dateFormatter dateFromString:dateString];
x.labelFormatter    =   timeFormatter;   

我认为这个逻辑失败了，因为每个月的天数不同。现在月份在 x 轴上显示，但它显示为

1 月、3 月、4 月、5 月、5 月、6 月、7 月、8 月、9 月、10 月、11 月、12 月。

您可以看到没有 2 月，而 5 月有 2 个条目。我的刻度间隔如何与每个月的天数相关。有什么解决办法吗？ 感谢和问候，

Answer 1

我遇到了同样的问题。我的快速而肮脏的解决方案是进行自定义标签，循环整个月并将时间戳添加到数组中。

x.labelingPolicy = CPAxisLabelingPolicyNone;

NSMutableArray *customLabels = [NSMutableArray arrayWithCapacity:12];
NSMutableArray *customMajorTickLocations = [NSMutableArray arrayWithCapacity:12];
NSMutableArray *customMinorTickLocations = [NSMutableArray arrayWithCapacity:12];
NSDate* dateCurrentMonth = [[NSDate date] dateAtStartOfYear];

for (NSUInteger iMonth = 0; iMonth < 12; iMonth++)
{
    NSNumber* numMajorTickLocation = [NSNumber numberWithDouble:[dateCurrentMonth timestampAtMidnight]];
    NSNumber* numMinorTickLocation = [NSNumber numberWithDouble:[dateCurrentMonth timestampAtMidnight]+14*oneDay];

CPAxisLabel *newLabel = [[CPAxisLabel alloc] initWithText:[dateFormatter stringFromDate:dateCurrentMonth] textStyle:x.labelTextStyle];
newLabel.tickLocation = [numMinorTickLocation decimalValue];
newLabel.offset = x.labelOffset + x.majorTickLength;

dateCurrentMonth = [[dateCurrentMonth dateByAddingDays:32] dateAtStartOfMonth];

[customLabels addObject:newLabel];
[customMajorTickLocations addObject:numMajorTickLocation];
[customMinorTickLocations addObject:numMinorTickLocation];
[newLabel release];

}

// add a last major tick to close the range
[customMajorTickLocations addObject:[NSNumber numberWithDouble:[dateCurrentMonth timestampAtMidnight]]];

x.axisLabels = [NSSet setWithArray:customLabels];
x.majorTickLocations = [NSSet setWithArray:customMajorTickLocations];
x.minorTickLocations = [NSSet setWithArray:customMinorTickLocations];

Answer 2

刚刚回答了一个相关问题。使用 CPTCalendarFormatter 而不是 CPTTimeFormatter，这在您必须以秒为单位设置时间间隔偏移量（例如小时 = 60*60，日 = 24*60*60）时很好，但月份的天数/秒数（30* 24*60*60 或 31*24*60*60, 28, 闰年 ecc.)。 CPTCalendarFormatter 让您决定标签上日期计算的日历单位。这样，固定了参考日期和参考日历单位，在数据源方法中，您将必须返回从参考日期开始的这些单位的数量。

这是完整的代码，享受吧。

在您的 viewDidLoad 或其他地方初始化图表：

[...]

// Graph host view
CPTGraphHostingView* hostView = [[CPTGraphHostingView alloc] initWithFrame:self.view.frame];
[self.view addSubview: hostView];

// Your graph
CPTGraph* graph = [[CPTXYGraph alloc] initWithFrame:hostView.bounds];
hostView.hostedGraph = graph;
CPTXYAxisSet *axisSet = (CPTXYAxisSet *)[graph axisSet];    

// xAxis configuration
CPTXYAxis *xAxis = [axisSet xAxis];
[xAxis setLabelingPolicy:CPTAxisLabelingPolicyFixedInterval];
// Prepare dateFormat for current Locale, we want "JAN 2014" "FEB 2014" and so on
NSString *dateComponents = @"MMMYY";
NSString *localDateFormat = [NSDateFormatter dateFormatFromTemplate:dateComponents options:0 locale:[NSLocale currentLocale]];
NSDateFormatter *labelDateFormatter=[[NSDateFormatter alloc] init];
labelDateFormatter.dateFormat=localDateFormat;    
// Set xAxis date Formatter
CPTCalendarFormatter *xDateYearFormatter = [[CPTCalendarFormatter alloc] initWithDateFormatter:labelDateFormatter];
//Keep in mind this reference date, it will be used to calculate NSNumber in dataSource method
xDateYearFormatter.referenceDate = [NSDate dateWithTimeIntervalSince1970:0];
xDateYearFormatter.referenceCalendarUnit=NSMonthCalendarUnit;    
[xAxis setLabelFormatter:xDateYearFormatter];

// yAxis configuration
CPTXYAxis *yAxis = [axisSet yAxis];
[yAxis setMajorIntervalLength:CPTDecimalFromFloat(_YOURYINTERVAL_)];
[yAxis setLabelingPolicy:CPTAxisLabelingPolicyFixedInterval];
[yAxis setLabelFormatter:_YOURYFORMATTER_];
[yAxis setAxisConstraints:[CPTConstraints constraintWithLowerOffset:0.0]]

// Get the (default) plotspace from the graph so we can set its x/y ranges
CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *) graph.defaultPlotSpace;
NSDate *startDate=_YOURSTARTINGDATE_
//Number of months since the reference date
NSInteger xStart=[[[NSCalendar currentCalendar] components: NSCalendarUnitMonth
                                 fromDate: xDateYearFormatter.referenceDate
                                   toDate: _YOURSTARTINGDATE_
                                  options: 0] month];    
[plotSpace setXRange: [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(xStart)     length:CPTDecimalFromInteger(_YOURDATESARRAY_.count-1)]];
[plotSpace setYRange: [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.0) length:CPTDecimalFromFloat(_YOURMAXYVALUE_)]];

[...]

在轴上返回值的数据源方法：

 -(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index
{
    switch (fieldEnum) {

        case CPTScatterPlotFieldX: {

            NSInteger monthsOffset=[[[NSCalendar currentCalendar] components: NSCalendarUnitMonth  fromDate: [NSDate dateWithTimeIntervalSince1970:0] toDate: [_YOURDATESARRAY_ objectAtIndex:index] options: 0] month];                
            NSNumber *val = [NSNumber numberWithInteger:monthsOffset];    
            return val;
            break;
        }
        case CPTScatterPlotFieldY: {
            NSNumber *val=_YOURVALUEFORYAXIS_;
            return val;
            break;
        }
        default:
            break;
    }

    return nil;
}