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考虑以下代码:

公共类 CrewDatabaseForm

Public Shared CrewList As List(Of String)

Private Sub CrewDatabaseForm_FormClosed(sender As Object, e As FormClosedEventArgs) Handles Me.FormClosed
    Dim CL As New List(Of String)
    If DataGridView1.Rows.Count = 2 Then CL.Add(DataGridView1.Rows(0).Cells(0).Value)
    If DataGridView1.Rows.Count > 2 Then
        For i As Integer = 0 To (DataGridView1.Rows.Count - 2)
            CL.Add(DataGridView1.Rows(i).Cells(0).Value.ToString)
        Next
    End If
    MessageBox.Show(DataGridView1.Rows.Count.ToString)


End Sub


Private Sub CrewDatabaseForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

End Sub

结束类

--这个表格只是一个datagridview。每当我退出表单并开始 if 和 for 语句时,如果我在第一列中输入了一个值并且没有按下输入,则会发生错误:

“Stage Tally.exe 中发生了‘System.NullReferenceException’类型的异常,但未在用户代码中处理

附加信息:对象引用未设置为对象的实例。

如果有这个异常的处理程序,程序可以安全地继续。”

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