我有一个核心图线图，显示如下（为清楚起见，背景视图为红色）：
我在底部有 0 填充，并且配置了带有标签的 x 轴。不过，该图被挤压到视图的底部。如果我增加底部填充，我会在底部得到一个灰色条，结果相同。
为了从视图底部向上移动图形并显示轴，我需要更改什么？
代码很长，但这里有一些摘录：
self->graph = [[CPTXYGraph alloc] initWithFrame:hostView.bounds];
hostView.hostedGraph = graph;
self->graph.paddingLeft = 0.0f;
self->graph.paddingTop = 10.0f;
self->graph.paddingRight = 0.0f;
self->graph.paddingBottom = 0.0f;
...
[plotSpace scaleToFitPlots:[NSArray arrayWithObjects:p1, p2, p3, nil]];
CPTMutablePlotRange *xRange = [plotSpace.xRange mutableCopy];
[xRange expandRangeByFactor:CPTDecimalFromCGFloat(1.1f)];
plotSpace.xRange = xRange;
CPTMutablePlotRange *yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.0f) length:CPTDecimalFromFloat(500.0f)];
plotSpace.yRange = yRange;
...
CPTXYAxisSet *axisSet = (CPTXYAxisSet *) self->graph.axisSet;
CPTAxis *x = axisSet.xAxis;
x.axisLineStyle = axisLineStyle;
x.labelingPolicy = CPTAxisLabelingPolicyNone;
x.majorTickLineStyle = axisLineStyle;
x.majorTickLength = 4.0f;
x.tickDirection = CPTSignNegative;
...
x.axisLabels = xLabels;
x.majorTickLocations = xLocations;