继前一篇文章提到关于使用C#绘制条形图的思路之后，这里接着介绍绘制饼图的思路。本篇文章所涉及的源代码是在前面的基础上完成的，在本文的最后，将会提供本实例的完整代码下载地址，有兴趣的朋友可以下载。
    言归正传，开始介绍饼图的绘制。其实，饼图的绘制跟条形图的绘制有颇多相似之处，其大体亦经过以下几个步骤：
    （1）创建Graphics对象实例；
    （2）设置图形及文本属性；
    （3）设置画布及边框；
    （4）绘制标题文本；
    （5）循环绘制扇形图并最终组合成饼图，这里利用了FillPie方法；
    （6）绘制图例。
    饼图的绘制在类PieGraph中实现，以下为其代码示例：
using System; using System.Data; using System.Drawing; using System.Drawing.Text; using System.Drawing.Drawing2D; using System.Collections.Generic; namespace GraphDrawing { class PieGraph { #region Member fields /// <summary> /// The color list for each bar drawing /// </summary> private List<Color> m_colorList; /// <summary> /// The data for <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> drawing /// </summary> private DataTable m_dataTable; /// <summary> /// The width of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> private int m_width; /// <summary> /// The height of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> private int m_height; /// <summary> /// The legend width of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> private int m_legendWidth; #endregion #region Public properties /// <summary> /// The title of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> public <a class="tags" href="/tags/STRING.html" title=string>string</a> GraphTitle { get; set; } /// <summary> /// The font format of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> public <a class="tags" href="/tags/STRING.html" title=string>string</a> FontFormat { get; set; } #endregion /// <summary> /// Constructor with arguments /// </summary> /// <param name="width">the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> width</param> /// <param name="height">the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> height</param> /// <param name="legendWidth">the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> legend width</param> /// <param name="dataTable">the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> data</param> public PieGraph(int width, int height, int legendWidth, DataTable dataTable) { m_width = width; m_height = height; m_legendWidth = legendWidth; m_dataTable = dataTable; m_colorList = Utils.GetColorList(); } /// <summary> /// Generate Pie <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> /// <returns>bitmap</returns> public Bitmap DrawPieGraph() { int iPieDiameter = m_width < (m_height + 150) ? (m_width - 250) : (m_height - 150); // Calculate the sum <a class="tags" href="/tags/FLOAT.html" title=float>float</a> fSum = 0; foreach (DataRow row in m_dataTable.Rows) { fSum += Convert.ToSingle(row[1]); } // Create an object of Graphics Bitmap bitmap = new Bitmap(m_width, m_height); Graphics <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> = Graphics.FromImage(bitmap); // Set the attribute of bar and text <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.ScaleTransform(1, 1); <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.SmoothingMode = SmoothingMode.Default; <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.TextRenderingHint = TextRenderingHint.AntiAlias; // Set the canvas and the border <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.Clear(Color.White); <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.DrawRectangle(Pens.Green, 0, 0, m_width - 5, m_height - 5); // Draw the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> title <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.DrawString(GraphTitle, new Font(FontFormat, 14), Brushes.Black, new PointF(7, 35)); // Draw the pie <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> <a class="tags" href="/tags/FLOAT.html" title=float>float</a> fCurrentAngle = 0; <a class="tags" href="/tags/FLOAT.html" title=float>float</a> fTotalAngle = 0; for (int i = 0; i < m_dataTable.Rows.Count; i++) { fCurrentAngle = Convert.ToSingle(m_dataTable.Rows[i][1]) / fSum * 360; <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.FillPie(new SolidBrush(m_colorList[i]), 50, 75, iPieDiameter, iPieDiameter, fTotalAngle, fCurrentAngle); <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>.DrawPie(Pens.Black, 50, 75, iPieDiameter, iPieDiameter, fTotalAngle, fCurrentAngle); fTotalAngle += fCurrentAngle; } // Draw the legend of <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> bitmap = DrawLegend(bitmap); return bitmap; } /// <summary> /// Generate the legend /// </summary> /// <param name="<a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>"></param> /// <returns></returns> private Bitmap DrawLegend(Bitmap <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>) { Bitmap bitmap = new Bitmap(250, m_height); Graphics objGraphic = Graphics.FromImage(bitmap); Graphics <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>ic = Graphics.FromImage(<a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>); int i, x; for (i = 0, x = m_legendWidth; i < m_dataTable.Rows.Count; i++) { //Draw the bar SolidBrush brush = new SolidBrush(m_colorList[i]); objGraphic.FillRectangle(brush, 10, m_height - 90 - x, m_legendWidth, m_legendWidth); <a class="tags" href="/tags/STRING.html" title=string>string</a> drawString = m_dataTable.Rows[i][0].ToString() + " - " + m_dataTable.Rows[i][1].ToString(); Font drawFont = new Font(FontFormat, 8); SolidBrush drawBrush = new SolidBrush(Color.Black); objGraphic.DrawString(drawString, drawFont, drawBrush, m_legendWidth * 2, m_height - 90 - x); //x axis spacing by m_legendWidth + 5 x += m_legendWidth + 5; } // Draw the <a class="tags" href="/tags/STRING.html" title=string>string</a> and the rectangle for the legend <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>ic.DrawRectangle(new Pen(Color.Purple, 1), m_width - 180, m_height - 85 - x, 160, x + 10); <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>ic.DrawString("Legend", new Font(FontFormat, 11, FontStyle.Bold), Brushes.Purple, new PointF(m_width - 180, m_height - 110 - x)); <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>ic.DrawImage(bitmap, m_width - 180, 10); return (<a class="tags" href="/tags/GRAPH.html" title=graph>graph</a>); } } }

    同样，在WinForm中调用亦非常简单，代码示例如下：
/// <summary> /// Draw the pie <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> /// </summary> private void DrawPieGraph() { this.ReadInputData(); <a class="tags" href="/tags/STRING.html" title=string>string</a> strTitle = txtGraphTitle.Text; <a class="tags" href="/tags/STRING.html" title=string>string</a> strFont = "Courier"; int iWidth = picPieGraph.Width; int iHeight = picPieGraph.Height; int iLegendWidth = (iWidth - 200) / (m_dataTable.Rows.Count * 2); PieGraph pieGraph = new PieGraph(iWidth, iHeight, iLegendWidth, m_dataTable); pieGraph.GraphTitle = strTitle; pieGraph.FontFormat = strFont; // Output the <a class="tags" href="/tags/GRAPH.html" title=graph>graph</a> to the picture box picPieGraph.Image = pieGraph.DrawPieGraph(); }

    最终的饼图绘制界面效果如下图所示：

    整个绘图程序的源代码可以从以下地址下载：http://download.csdn.net/source/2386682。到此，利用C#的GDI+绘制条形图和饼图就介绍到这里，这里介绍的都是很基本的方法，并未作深入探讨，更深层次的研究有待日后继续。绘图，就是如此简单。