vb代码如下：
Imports

Public Class Form1
    Enum DiceNames
        SNAKE_EYES = 2
        TREY = 3
        CRAPS = 7
        LUCK_SEVEN = 7
        YO_LEVEN = 11
        BOX_CARS = 12
    End Enum

    Const m_strFILE_PREFIX As String = "\imges\die"
    Const m_strFILE_SUFFIX As String = ".png"

    Dim m_intMyPoint As Integer = 0
    Dim m_objRandomObject As Random = New Random

    Private Sub btnPlay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPlay.Click
        m_intMyPoint = 0
        gbDisplay.Text = "Point"
        lblResult.Text = ""

        picDie3 = Nothing
        picDie4 = Nothing

        Dim intSum As Integer = RollDice()

        Select Case intSum
            Case DiceNames.LUCK_SEVEN, DiceNames.YO_LEVEN
                btnRoll.Enabled = False
                lblResult.Text = "你赢了！"
            Case DiceNames.SNAKE_EYES, DiceNames.TREY, _
                DiceNames.BOX_CARS
                btnRoll.Enabled = False
                lblResult.Text = "你输了！"
            Case Else
                m_intMyPoint = intSum
                gbDisplay.Text = "Point Is " & intSum
                lblResult.Text = "再来一次！"
               
                picDie3.Image = picDie1.Image//这个地方总是出错，错误提示为“未将对象引用设置到对象的实例”
                picDie4.Image = picDie2.Image
               
                btnPlay.Enabled = False
                btnRoll.Enabled = True
        End Select
    End Sub

    Private Sub btnRoll_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRoll.Click
        Dim intSum As Integer = RollDice()

        If intSum = m_intMyPoint Then
            lblResult.Text = "你赢了！"
            btnPlay.Enabled = True
            btnRoll.Enabled = False
        ElseIf intSum = DiceNames.CRAPS Then
            lblResult.Text = "你输了"
            btnRoll.Enabled = False
            btnPlay.Enabled = True
        End If
    End Sub

    Function RollDice() As Integer
        Dim intDie1 As Integer = m_objRandomObject.Next(1, 7)
        Dim intDie2 As Integer = m_objRandomObject.Next(1, 7)

        DisplayDie(picDie1, intDie1)
        DisplayDie(picDie2, intDie2)

        Return (intDie1 + intDie2)
    End Function

    Sub DisplayDie(ByRef picDie As PictureBox, ByRef intFace As Integer)
        picDie.Image = _
           Image.FromFile(Directory.GetCurrentDirectory & m_strFILE_PREFIX & intFace & m_strFILE_SUFFIX)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        btnRoll.Enabled = False
    End Sub
End Class
调试总是出错，哪位帮帮忙？？
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