继续上一期《绘图实例之统计图2》，继续讲解如何绘制饼图：

当按下“饼图”按钮时，调用三个函数，分别是绘制饼图、显示到窗口，由于不需要坐标轴，所以这里不再绘制坐标轴：

    Private Sub btnPie_Click(sender As Object,e As EventArgs) Handles btnPie.Click
        Call DrawPie()
        Call DrawToForm()
    End Sub

DrawToForm()在之前已经介绍，以下是DrawPie的代码：

    '绘制饼图
    Private Sub DrawPie()
        '标注每个季度
        Dim seasonValue(3) As Integer
        seasonValue(0) = nudSeason1.Value
        seasonValue(1) = nudSeason2.Value
        seasonValue(2) = nudSeason3.Value
        seasonValue(3) = nudSeason4.Value
        Dim seasonName() As String = {"一季度","二季度","三季度","四季度"}
        '我们要获得4个季度总的盈利
        Dim seasonSum As Integer = 0
        For i As Integer = 0 To 3
            seasonSum += seasonValue(i)
        Next
        '根据总赢利情况，来获得每个季度在饼图中所占的份额（角度）
        '为了简化起见，这里直接取整数
        Dim seasonAngle(4) As Integer
        seasonAngle(0) = 0
        seasonAngle(1) = seasonValue(0) * 360 \ seasonSum
        seasonAngle(2) = seasonValue(1) * 360 \ seasonSum + seasonAngle(1)
        seasonAngle(3) = seasonValue(2) * 360 \ seasonSum + seasonAngle(2)
        seasonAngle(4) = 360
        '分别用4种颜色表示不同季度的盈利--http://blog.csdn.net/uruseibest
        Dim seasonColor() As Color = {Color.Red,Color.Blue,Color.Green,Color.GreenYellow}
        For i As Integer = 0 To 3
            g.FillPie(New SolidBrush(seasonColor(i)),New Rectangle(100,100,200,200),seasonAngle(i),seasonAngle(i + 1) - seasonAngle(i))
            '饼图中特别需要说明每个季度对应的颜色
            g.FillRectangle(New SolidBrush(seasonColor(i)),New Rectangle(360,i * 50 + 80,60,40))
            '标出每个季度
            g.DrawString(seasonName(i),New Font("宋体",12),New SolidBrush(Color.Black),New Point(450,i * 50 + 90))
        Next

    End Sub

按下“饼图”按钮时，如下图所示：

需要强调的是FillPie()最后两个关于角度的参数：
第1个角度参数（startAngle）：扇形起始角度，是构成扇形的第一条边从x轴方向按照顺时针旋转的角度。
第2个角度参数（sweepAngle）：扇形第二条边从第一条边按照顺时针方向旋转的角度

由于.net平台下C#和vb.NET很相似，本文也可以为C#爱好者提供参考。

学习更多vb.net知识，请参看 vb.net 教程 目录