Visual Studio 2017中DrawArc抛出System.ArgumentException问题求助

我正在开发四冲程循环仿真程序，在Visual Studio 2017中调试时触发了System.ArgumentException异常，不知如何解决。

相关代码（已替换$exception为Mygraphics） #

Private Sub Animation(q2)
    Dim MyGraphics As Graphics
    MyGraphics = Me.CreateGraphics
    Dim Mycolor As Color = Color.FromArgb(0, 255, 0)
    Dim MyPen As New Pen(Color.Green, 1)
    Dim ox, oy, ax, ay, bx, by, crank_length, conrod_length
    Dim k
    Dim q, r As Integer
    MyGraphics.Clear(Color.WhiteSmoke)
    Call position_analysis(q2)
    k = 800
    crank_length = r2 * k
    conrod_length = r3 * k
    '------------------
    ox = 150
    oy = 300
    ax = ox + crank_length * Math.Cos(q2)
    ay = oy - crank_length * Math.Sin(q2)
    bx = ax + conrod_length * Math.Cos(q3)
    by = oy
    '------------------
    r = crank_length
    q = q2 * 180 / pi
    If q > 360 Then q = q - 360
    q = 360 - q
    MyGraphics.DrawArc(MyPen, ox - r, oy - r, 2 * r, 2 * r, q, 90)
    '-------------------
    LineShape1.X1 = ox
    LineShape1.Y1 = oy
    LineShape1.X2 = ox + crank_length + conrod_length + 100
    LineShape1.Y2 = oy
    LineShape2.X1 = ox
    LineShape2.Y1 = ox
    LineShape2.X2 = ax
    LineShape2.Y2 = ay
    LineShape3.X1 = ax
    LineShape3.Y1 = ay
    LineShape3.X2 = bx
    LineShape3.Y2 = by
    OvalShape1.Location = New Point(ox - OvalShape1.Width / 2, oy - OvalShape1.Height / 2)
    OvalShape2.Location = New Point(ax - OvalShape2.Width / 2, ay - OvalShape2.Height / 2)
    OvalShape3.Location = New Point(bx - OvalShape3.Width / 2, by - OvalShape3.Height / 2)
    RectangleShape1.Location = New Point(bx - RectangleShape1.Width / 2, by - RectangleShape1.Height / 2)
End Sub

异常相关截图信息 #

• 截图1：调试时触发System.ArgumentException，提示“参数无效”，异常指向MyGraphics.DrawArc代码行
• 截图2：显示异常的详细调用栈，确认异常源自GDI+绘图操作的参数错误

问题排查与解决步骤 #

核心问题分析 #

System.ArgumentException在DrawArc触发，通常是因为参数不符合GDI+要求：

1. 绘图矩形的宽度/高度（第4、5个参数）为非正数
2. 角度参数超出合法范围或类型不匹配
3. 变量未正确初始化导致数值异常

具体修复措施 #

• 明确变量类型，避免Variant隐患：
  原代码大量变量未声明类型，默认是Variant，容易引发类型转换错误。修改变量声明：

  Dim ox As Integer, oy As Integer, ax As Double, ay As Double, bx As Double, by As Integer
  Dim crank_length As Double, conrod_length As Double
  Dim k As Integer = 800
  Dim q As Single, r As Integer
  

• 修复LineShape2的坐标错误：
  原代码LineShape2.Y1 = ox是明显错误，应该改为oy，否则控件位置异常可能间接引发问题：

  LineShape2.Y1 = oy
  

• 确保DrawArc参数合法：

  • 检查r2、r3在position_analysis(q2)执行后是否被赋值为正数，否则crank_length会为非正数，导致2*r无效
  • 将角度变量q改为Single类型（匹配DrawArc的参数要求），避免整数转换丢失精度：

    q = CSng(q2 * 180 / Math.PI)
    

  • 添加参数合法性判断，避免无效绘图：

    If r > 0 Then
        MyGraphics.DrawArc(MyPen, ox - r, oy - r, 2 * r, 2 * r, q, 90)
    End If
    

• 优化GDI资源管理：
  使用Using语句自动释放Pen资源，避免内存泄漏：

  Using MyPen As New Pen(Color.Green, 1)
        MyGraphics.DrawArc(MyPen, ox - r, oy - r, 2 * r, 2 * r, q, 90)
        ' 其他使用MyPen的绘图操作也放在这里
    End Using
  

• 验证MyGraphics对象有效性：
  添加非空判断，避免空引用异常：

  If MyGraphics IsNot Nothing Then
      MyGraphics.Clear(Color.WhiteSmoke)
      ' 后续绘图操作
  End If
  

内容的提问来源于stack exchange，提问作者IJH