Question

这就是发生的事情：在我的应用程序的表单加载中，我创建了一个后台工作程序来绑定我的控件上的集合（来自数据集中填充的数据库的记录）。但问题是当我更新数据库上的记录时，如果我再次运行此程序，则会抛出错误。

    If xControl.InvokeRequired Then
        Dim MyDelegate As New InitializeDataBinding_Delegate(AddressOf InitializeDataBinding)
        Invoke(MyDelegate, New Object() {xControl, xQuery, xPrimaryKey}) ' ERROR HERE SAYING: Collection was modified; enumeration operation may not execute.
    Else
        Using ds As DataSet = New DataSet()
            Using dbAdapter As MySqlDataAdapter = New MySqlDataAdapter(xQuery, ConnectionClass.ConnectionString)
                dbAdapter.Fill(ds)
            End Using

            Dim dvm As DataViewManager = New DataViewManager(ds)
            Dim iDataList As DataView = dvm.CreateDataView(ds.Tables(0))
            For Each iBind As Binding In xControl.DataBindings
                xControl.DataBindings.Remove(iBind)
            Next
            xControl.DataBindings.Add("EditValue", iDataList, xPrimaryKey)
            xControl.Properties.DataSource = iDataList
            xControl.EditValue = Nothing
            txtStatus.Text = "Ready"
        End Using
    End If

Answer 1

使用For Each迭代时，必须避免集合中的更新。使用简单的For循环而不是For Each。

Answer 2

您不能使用For Each循环从diction或KeyValuePair中删除项目，但您可以使用常规for循环，获取密钥并使用密钥从列表中删除该项目。

      For i As Integer = 0 To oDictionary.Count - 1
        Dim sKey = m_oDictionary.ElementAt(i).Key
        m_oDictionary.Remove(sKey)
      Next

Answer 3

通过添加：

解决

xControl.DataBindings.Clear()

If xControl.InvokeRequired Then
    Dim MyDelegate As New InitializeDataBinding_Delegate(AddressOf InitializeDataBinding)
    Invoke(MyDelegate, New Object() {xControl, xQuery, xPrimaryKey}) ' ERROR HERE SAYING: Collection was modified; enumeration operation may not execute.
Else
    Using ds As DataSet = New DataSet()
        Using dbAdapter As MySqlDataAdapter = New MySqlDataAdapter(xQuery, ConnectionClass.ConnectionString)
            dbAdapter.Fill(ds)
        End Using

        xControl.DataBindings.Clear() 'HERE

        Dim dvm As DataViewManager = New DataViewManager(ds)
        Dim iDataList As DataView = dvm.CreateDataView(ds.Tables(0))
        For Each iBind As Binding In xControl.DataBindings
            xControl.DataBindings.Remove(iBind)
        Next
        xControl.DataBindings.Add("EditValue", iDataList, xPrimaryKey)
        xControl.Properties.DataSource = iDataList
        xControl.EditValue = Nothing
        txtStatus.Text = "Ready"
    End Using
End If

Answer 4

        Dim index As Integer = 0
opnieuw:
        For Each F In openbestand.file
            If F.Contains("~$") Then
                openbestand.file.Remove(openbestand.file(index))
                openbestand.path.Remove(openbestand.path(index))
                GoTo opnieuw
            Else
                index = (index + 1)
            End If
    Next

Answer 5

如果要使用循环，则需要确保索引小于Count，因为每次删除关键元素时计数都会减少：

Dim i As Integer

For i = 0 To dictionary1.Count - 1
    If i <= dictionary1.Count - 1 Then
        Dim sKey = dictionary1.ElementAt(i).Key
        dictionary1.Remove(sKey)
    End If
Next

VBNet错误：集合被修改;枚举操作可能无法执行

5 个答案: