Question

大家好我的项目中有一行代码得到一个空引用运行时错误，但是如果我断点它然后单步执行它一切正常。任何想法

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim checkbox_l As String = "CheckBox"
    Dim checkbox_i As string
    For i As Integer = 1 To id Step 1
        checkbox_i = checkbox_l + i.ToString
        Try
            If CType(Panel1.Controls(checkbox_i), CheckBox).Checked = True Then
                My.Settings.name = Panel1.Controls("CheckBox" & i).Text
                Call installer_properties()
                Call start_install()
            End If
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    Next
End Sub

代码用于检查是否已选中动态创建的复选框，然后相应地继续，但是我在行中出错

If CType(Panel1.Controls(checkbox_i), CheckBox).Checked = True Then

Answer 1

使用Debug.Assert来捕捉它

Dim c as Control = Panel1.Controls(checkbox_i)
Debug.Assert(c IsNot Nothing)
Dim cb as CheckBox = TryCast(c, CheckBox)
If cb isNot Nothing Then
   If cb.Checked = True Then
      My.Settings.name = cb.Text
      Call installer_properties()
      Call start_install()
   End If
End If

Answer 2

如果选中则获得结果1和0 - 如果不是，则可以写下：

textbox1.text = Microsoft.VisualBasic.Right（Panel1.Controls（＆＃34; CheckBox＆＃34;＆amp; i）.ToString，1）

空引用异常运行时错误

2 个答案: