错误：在不是结构或联合的东西中请求成员“界限”

Question

使用 core-plot 框架编译 iPhone 应用程序时出现上述错误。我将此视图控制器的视图链接到 IB 中的 CPLayerHostingView。这是 viewDidLoad() 函数的示例代码。

- (void)viewDidLoad {
    [super viewDidLoad];

    graph = [[CPXYGraph alloc] initWithFrame: self.view.bounds];

    CPLayerHostingView *hostingView = (CPLayerHostingView *)self.view;
    hostingView.hostedLayer = graph;


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


    CPXYPlotSpace *plotSpace = (CPXYPlotSpace *)graph.defaultPlotSpace;
    plotSpace.xRange = [CPPlotRange plotRangeWithLocation:CPDecimalFromFloat(-6)
                                                   length:CPDecimalFromFloat(12)];
    plotSpace.yRange = [CPPlotRange plotRangeWithLocation:CPDecimalFromFloat(-5)
                                                   length:CPDecimalFromFloat(30)];

    CPLineStyle *lineStyle = [CPLineStyle lineStyle];
    lineStyle.lineColor = [CPColor blackColor];
    lineStyle.lineWidth = 2.0f;

    CPXYAxisSet *axisSet = (CPXYAxisSet *)graph.axisSet;
    axisSet.xAxis.majorIntervalLength = [[NSDecimalNumber decimalNumberWithString:@"5"] decimalValue];
    axisSet.xAxis.minorTicksPerInterval = 4;
    axisSet.xAxis.majorTickLineStyle = lineStyle;
    axisSet.xAxis.minorTickLineStyle = lineStyle;
    axisSet.xAxis.axisLineStyle = lineStyle;
    axisSet.xAxis.minorTickLength = 5.0f;
    axisSet.xAxis.majorTickLength = 7.0f;
    axisSet.xAxis.axisLabelOffset = 3.0f;

    axisSet.yAxis.majorIntervalLength = [[NSDecimalNumber decimalNumberWithString:@"5"] decimalValue];
    axisSet.yAxis.minorTicksPerInterval = 4;
    axisSet.yAxis.majorTickLineStyle = lineStyle;
    axisSet.yAxis.minorTickLineStyle = lineStyle;
    axisSet.yAxis.axisLineStyle = lineStyle;
    axisSet.yAxis.minorTickLength = 5.0f;
    axisSet.yAxis.majorTickLength = 7.0f;
    axisSet.yAxis.axisLabelOffset = 3.0f;

    CPScatterPlot *xSquaredPlot = [[[CPScatterPlot alloc] initWithFrame:graph.defaultPlotSpace.bounds] autorelease];
    xSquaredPlot.identifier = @"X Squared Plot";
    xSquaredPlot.dataLineStyle.lineWidth = 1.0f;
    xSquaredPlot.dataLineStyle.lineColor = [CPColor redColor];
    xSquaredPlot.dataSource = self;
    [graph addPlot:xSquaredPlot];

    CPPlotSymbol *greenCirclePlotSymbol = [CPPlotSymbol ellipsePlotSymbol];
    greenCirclePlotSymbol.fill = [CPFill fillWithColor:[CPColor greenColor]];
    greenCirclePlotSymbol.size = CGSizeMake(2.0, 2.0);

    [xSquaredPlot setPlotSymbol:greenCirclePlotSymbol];

    CPScatterPlot *xInversePlot = [[[CPScatterPlot alloc] initWithFrame:graph.defaultPlotSpace.bounds] autorelease];
    xInversePlot.identifier = @"X Inverse Plot";
    xInversePlot.dataLineStyle.lineWidth = 1.0f;
    xInversePlot.dataLineStyle.lineColor = [CPColor blueColor];
    xInversePlot.dataSource = self;
    [graph addPlot:xInversePlot];
}

问题线如下：

CPScatterPlot *xSquaredPlot = [[[CPScatterPlot alloc] initWithFrame:graph.defaultPlotSpace.bounds] autorelease];
CPScatterPlot *xInversePlot = [[[CPScatterPlot alloc] initWithFrame:graph.defaultPlotSpace.bounds] autorelease];

这是说 graph.defaultPlotSpace 没有“界限”。有人也遇到过这种情况吗？

Answer 1

用括号语法尝试这些调用。

CPScatterPlot *xSquaredPlot = [[[CPScatterPlot alloc] initWithFrame:[[graph defaultPlotSpace] bounds]] autorelease];
CPScatterPlot *xInversePlot = [[[CPScatterPlot alloc] initWithFrame:[[graph defaultPlotSpace] bounds]] autorelease];

Answer 2

作为图形的 defaultPlotSpace 返回的 CPXYPlotSpace 是 CPPlotSpace 的子类，它只是 NSObject 的子类。这些类都没有定义边界属性。相反，CPXYPlotSpace 让您通过 CPPlotRange 对象设置范围，正如您在检索 defaultPlotSpace 后的前两行中看到的那样。

做你想做的事情的正确方法是分配地块并只使用-init，而不是-initWithFrame:。当这些图被添加到图中时，我相信它们会根据绘图空间自动调整大小。或者，您可以使用 -initWithFrame: 并使用图形的框架。

如果您想查看从 CPXYPlotSpace 返回边界的便捷方法，请在mailing list 中告诉我们。

Answer 3

如果没有包含 Quartzcore 框架，则通过添加 Quartzcore 框架来解决此错误的问题。