Question

我有一个对象数组，我通过索引找到项目，分配一个值，但然后查看数组，该项目没有显示更新的值。

Public Structure Cheque
    Public Id As String
    Public Status As Byte
    Public Amount As String
    Public WarrantNo As String
End Structure

Public Class ChequeCollection

    Private chequeColl() As Cheque 'This is populated ok

Public Sub UpdateChequeAmount(ByVal Id As String, ByVal Amount As String)
        SyncLock lockObject
            Dim idx As Integer = Get_idx(Id) 'Finds it ok
            If idx <> -1 Then
                Dim cheque As Cheque = chequeColl(idx)
                cheque.Amount = Amount 'Updates value ok but if you look in chequeColl the value isn't there
            End If
        End SyncLock
    End Sub

End Class

Answer 1

因为值类型被复制到所使用的任何地方 - 你正在更新check变量中的值类型的副本，而不是数组中的副本。

您需要更新数组中的副本：

            Dim cheque As Cheque = chequeColl(idx)
            cheque.Amount = Amount 'Updates value ok but if you look in chequeColl the value isn't there
            chequeColl(idx) = cheque

当然，总是值得阅读Lippert先生的"The Truth About Value Types"

Answer 2

Dim cheque As Cheque = chequeColl(idx)
cheque.Amount = Amount

使用：

chequeColl(idx).Amount = Amount

它是如何运作的？

为什么数组中的项目不会更新？

2 个答案: