（五）如何自定义ChartDirector的数据点标签

为图表上的数据点加上标签，可以起到注释的作用，能提高图表的可读性。本示例就为你演示如何在Web图表控件ChartDirector绘制的散点图上加上自定义标签。

主要有以下几个步骤：

• 本例中的红色玻璃球来自一个散射层，由 XYChart.addScatterLayer创建
• 自定义标签放在一个数组变量中，用Layer.addExtraField将标签作为图表的附加字段
• Layer.setDataLabelFormat设置数据标签格式，并显示附加字段
• 用Layer.setDataLabelStyle将数据标签的字体设置为8磅大小的Arial Bold字体
• Layer.setDataLabelStyle返回一个TextBox对象，表示数据标签的原型。在本例中，TextBox对象用于自定义数据标签的背景颜色、3D边框、位置移动和对齐

散点图上的数据点标签：

在ChartDirector图表上自定义数据点标签源代码：

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#include "chartdir.h"   int main(int argc, char *argv[]) {     // The XY points for the scatter chart     double dataX[] = {150, 400, 300, 1500, 800};     double dataY[] = {0.6, 8, 5.4, 2, 4};       // The labels for the points     const char *labels[] = {"Nano\n100", "SpeedTron\n200 Lite", "SpeedTron\n200",         "Marathon\nExtra", "Marathon\n2000"};       // Create a XYChart object of size 450 x 400 pixels     XYChart *c = new XYChart(450, 400);       // Set the plotarea at (55, 40) and of size 350 x 300 pixels, with a light grey     // border (0xc0c0c0). Turn on both horizontal and vertical grid lines with light     // grey color (0xc0c0c0)     c->setPlotArea(55, 40, 350, 300, 0xffffff, -1, 0xc0c0c0, 0xc0c0c0, -1);       // Add a title to the chart using 18 pts Times Bold Itatic font.     c->addTitle("Product Comparison Chart", "timesbi.ttf", 18);       // Add a title to the y axis using 12 pts Arial Bold Italic font     c->yAxis()->setTitle("Capacity (tons)", "arialbi.ttf", 12);       // Add a title to the x axis using 12 pts Arial Bold Italic font     c->xAxis()->setTitle("Range (miles)", "arialbi.ttf", 12);       // Set the axes line width to 3 pixels     c->xAxis()->setWidth(3);     c->yAxis()->setWidth(3);       // Add the data as a scatter chart layer, using a 15 pixel circle as the symbol     ScatterLayer *layer = c->addScatterLayer(DoubleArray(dataX, (int)(sizeof(dataX) /         sizeof(dataX[0]))), DoubleArray(dataY, (int)(sizeof(dataY) / sizeof(dataY[0])         )), "", Chart::GlassSphereShape, 15, 0xff3333, 0xff3333);       // Add labels to the chart as an extra field     layer->addExtraField(StringArray(labels, (int)(sizeof(labels) / sizeof(labels[0])         )));       // Set the data label format to display the extra field     layer->setDataLabelFormat("{field0}");       // Use 8pts Arial Bold to display the labels     TextBox *textbox = layer->setDataLabelStyle("arialbd.ttf", 8);       // Set the background to purple with a 1 pixel 3D border     textbox->setBackground(0xcc99ff, Chart::Transparent, 1);       // Put the text box 4 pixels to the right of the data point     textbox->setAlignment(Chart::Left);     textbox->setPos(4, 0);       // Output the chart     c->makeChart("scatterlabels.png");       //free up resources     delete c;     return 0; }

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