继续上一期《绘图实例之统计图1》，继续讲解如何绘制折线图：

当按下“折线图”按钮时，调用三个函数，分别是绘制坐标轴、绘制折线、显示到窗口：

    Private Sub btnLineChart_Click(sender As Object,e As EventArgs) Handles btnLineChart.Click
        Call DrawAxis()
        Call DrawLine()
        Call DrawToForm()
    End Sub

DrawAxis()和DrawToForm()在上一期中已经介绍，以下是DrawLine的代码：

    '绘制折线
    Private Sub DrawLine()
        '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"}

        '先要获得每个值所在的坐标点
        '为了显眼，绘制点的显示为一个直径为8的蓝色圆形
        Dim signX,signY As Integer
        '将每个坐标点存入数组，画折线时候需要
        Dim pointSign() As Point
        ReDim pointSign(3)
        For i As Integer = 0 To 3
            signX = (i + 1) * 80
            '不要忘了比例1：3--http://blog.csdn.net/uruseibest
            signY = 320 - seasonValue(i) * 3
            pointSign(i) = New Point(signX,signY)
            '请注意画园时候的Rectangle位置
            g.FillEllipse(New SolidBrush(Color.Blue),New Rectangle(signX - 4,signY - 4,8,8))
        Next
        '使用红色画折线
        Dim penSign As New Pen(Color.Red,2)
        '将四个坐标点连接起来，注意画的是三条线
        For i As Integer = 0 To 2
            g.DrawLine(penSign,pointSign(i),pointSign(i + 1))
        Next

        '标出每个季度
        Dim strX,strY As Integer
        For i As Integer = 0 To 3
            strX = (i + 1) * 80 - 15
            strY = 325
            g.DrawString(seasonName(i),New Font("黑体",10),New SolidBrush(Color.Blue),New Point(strX,strY))
        Next
    End Sub

按下“折线图”按钮时，如下图所示：

最后强调一下关于绘制矩形、圆形等时候需要注意的起点位置：

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