无法在CorePlot的X轴上绘制NSDate。

Question

我是新手，想在使用coreplot绘制的柱状图的x轴上显示NSdate（年份或月份或日），我已经查看了一些示例来绘制NSDate沿着x轴。但是我无法绘制...

请问有人可以提供绘制NSDate沿x轴的代码吗？ 谢谢

我尝试了stackoverflow上的以下代码，但无法在x轴上显示标签。

// If you make sure your dates are calculated at noon, you shouldn't have to 
// worry about daylight savings. If you use midnight, you will have to adjust
// for daylight savings time.
NSDate *refDate = [NSDate dateWithTimeIntervalSinceReferenceDate:31556926 * 10];
NSTimeInterval oneDay = 24 * 60 * 60;

// Invert graph view to compensate for iOS coordinates
//CGAffineTransform verticalFlip = CGAffineTransformMakeScale(1,-1);
// self.view.transform = verticalFlip;

 // allocate the graph within the current view bounds
graph = [[CPTXYGraph alloc] initWithFrame: self.view.bounds];

// assign theme to graph
CPTTheme *theme = [CPTTheme themeNamed:kCPTDarkGradientTheme];
[graph applyTheme:theme];

// Setting the graph as our hosting layer
CPTGraphHostingView *hostingView = [[CPTGraphHostingView alloc] initWithFrame:self.view.bounds];

[self.view addSubview:hostingView];

hostingView.hostedGraph = graph;

graph.paddingLeft = 20.0;
graph.paddingTop = 20.0;
graph.paddingRight = 20.0;
graph.paddingBottom = 150.0;

// setup a plot space for the plot to live in
CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)graph.defaultPlotSpace;
NSTimeInterval xLow = 0.0f;
// sets the range of x values
plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(xLow)
                                               length:CPTDecimalFromFloat(oneDay*5.0f)];
// sets the range of y values
plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.0) 
                                               length:CPTDecimalFromFloat(5)];

// plotting style is set to line plots
CPTMutableLineStyle *lineStyle = [CPTMutableLineStyle lineStyle];
lineStyle.lineColor = [CPTColor blackColor];
lineStyle.lineWidth = 2.0f;

// X-axis parameters setting
CPTXYAxisSet *axisSet = (id)graph.axisSet;
axisSet.xAxis.majorIntervalLength = CPTDecimalFromFloat(oneDay);
axisSet.xAxis.minorTicksPerInterval = 0;
axisSet.xAxis.orthogonalCoordinateDecimal = CPTDecimalFromString(@"1"); //added for date, adjust x line
axisSet.xAxis.majorTickLineStyle = lineStyle;
axisSet.xAxis.minorTickLineStyle = lineStyle;
axisSet.xAxis.axisLineStyle = lineStyle;
axisSet.xAxis.minorTickLength = 5.0f;
axisSet.xAxis.majorTickLength = 7.0f;
axisSet.xAxis.labelOffset = 3.0f;

// added for date
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
dateFormatter.dateStyle = kCFDateFormatterShortStyle;
CPTTimeFormatter *timeFormatter = [[[CPTTimeFormatter alloc] initWithDateFormatter:dateFormatter] autorelease];
timeFormatter.referenceDate = refDate;
axisSet.xAxis.labelFormatter = timeFormatter;

// Y-axis parameters setting    
axisSet.yAxis.majorIntervalLength = CPTDecimalFromString(@"0.5");
axisSet.yAxis.minorTicksPerInterval = 2;
axisSet.yAxis.orthogonalCoordinateDecimal = CPTDecimalFromFloat(oneDay); // added for date, adjusts y line
axisSet.yAxis.majorTickLineStyle = lineStyle;
axisSet.yAxis.minorTickLineStyle = lineStyle;
axisSet.yAxis.axisLineStyle = lineStyle;
axisSet.yAxis.minorTickLength = 5.0f;
axisSet.yAxis.majorTickLength = 7.0f;
axisSet.yAxis.labelOffset = 3.0f;


// This actually performs the plotting
CPTScatterPlot *xSquaredPlot = [[[CPTScatterPlot alloc] init] autorelease];

CPTMutableLineStyle *dataLineStyle = [CPTMutableLineStyle lineStyle];
//xSquaredPlot.identifier = @"X Squared Plot";
xSquaredPlot.identifier = @"Date Plot";

dataLineStyle.lineWidth = 1.0f;
dataLineStyle.lineColor = [CPTColor redColor];
xSquaredPlot.dataLineStyle = dataLineStyle;
xSquaredPlot.dataSource = self;

CPTPlotSymbol *greenCirclePlotSymbol = [CPTPlotSymbol ellipsePlotSymbol];
greenCirclePlotSymbol.fill = [CPTFill fillWithColor:[CPTColor greenColor]];
greenCirclePlotSymbol.size = CGSizeMake(2.0, 2.0);
xSquaredPlot.plotSymbol = greenCirclePlotSymbol;  

// add plot to graph
[graph addPlot:xSquaredPlot];

// Add some data
NSMutableArray *newData = [NSMutableArray array];
NSUInteger i;
for ( i = 0; i < 5; i++ ) {
    NSTimeInterval x = oneDay*i;
    id y = [NSDecimalNumber numberWithFloat:1.2*rand()/(float)RAND_MAX + 1.2];
    [newData addObject:
     [NSDictionary dictionaryWithObjectsAndKeys:
      [NSDecimalNumber numberWithFloat:x], [NSNumber numberWithInt:CPTScatterPlotFieldX], 
      y, [NSNumber numberWithInt:CPTScatterPlotFieldY], 
      nil]];
    NSLog(@"%@",newData);
}
plotData = [newData retain];

}

#pragma mark - Plot Data Source Methods
-(NSUInteger)numberOfRecordsForPlot:(CPTPlot *)plot
{
return plotData.count;
}

-(NSNumber *)numberForPlot:(CPTPlot *)plot field:(NSUInteger)fieldEnum recordIndex:     (NSUInteger)index
 {
NSDecimalNumber *num = [[plotData objectAtIndex:index] objectForKey:[NSNumber numberWithInt:fieldEnum]];
return num;
}

- Lakshmi Reddy

---

如果您已经查看了Core Plot中包含的DatePlot和Plot Gallery示例，但仍然遇到问题，请编辑您的问题以解释您迄今为止尝试过的内容（包括代码）。 - Eric Skroch

Answer 1

如果您想做类似这样的事情...（对于图片的大小我很抱歉，我不熟悉如何为SO调整图片大小），您需要为X轴定义自定义标签。请考虑以下代码片段（取自生成上述图像的代码）：

/* --Define some custom labels for the data elements-- */
// Note that x is defined as: CPTXYAxisSet *axisSet = (CPTXYAxisSet*)self.graph.axisSet;
//                                      CPTXYAxis *x = axisSet.xAxis;
x.labelingPolicy = CPTAxisLabelingPolicyNone; // This allows us to create custom axis labels for x axis
NSMutableArray *ticks = [NSMutableArray arrayWithCapacity:1];
for(unsigned int counter = 0; counter < [_axisLabelStrings count];counter++) {
    // Here the instance variable _axisLabelStrings is a list of custom labels
    [ticks addObject:[NSNumber numberWithInt:counter]];
}
NSUInteger labelLocation = 0;
NSMutableArray* customLabels = [NSMutableArray arrayWithCapacity:[_axisLabelStrings count]];
@try {
    for (NSNumber *tickLocation in ticks) {
        CPTAxisLabel *newLabel = [[CPTAxisLabel alloc] initWithText: [_axisLabelStrings objectAtIndex:labelLocation++] textStyle:x.labelTextStyle];
        newLabel.tickLocation = [tickLocation decimalValue];
        newLabel.offset = 3.0f;//x.labelOffset + x.majorTickLength could be useful here.
        newLabel.rotation = M_PI/3.5f;
        [customLabels addObject:newLabel];
        [newLabel release];
    }
}
@catch (NSException * e) {
    NSLog(@"An exception occurred while creating date labels for x-axis");
}
@finally {
    x.axisLabels =  [NSSet setWithArray:customLabels];  
}
x.majorTickLocations = [NSSet setWithArray:ticks];

请注意，_axisLabelStrings需要进行处理和排序。您需要获取NSDate，对其进行排序，并为标签生成NSString。

简而言之，这就是如何创建自定义标签。

- Dream Lane

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请问您能提供此问题的示例代码吗？我也遇到了同样的问题。谢谢。 - Programming Learner