从 VB.NET 对象数组列表中检索数据 [英] Retrieving data from a VB.NET arraylist of objects

问题描述

我正在尝试从对象的 ArrayList (.NET 1.1 Framework) 中检索正确的值:

I am trying to retrieve the correct value from an ArrayList of objects (.NET 1.1 Framework):

我定义了以下内容:

Public AlList As New ArrayList

Public Class ItemInfo
    Public ItemNo As Int16
    Public ItemType As String
    Public Reports As Array
    Public PDFs As Array
End Class

form_load 事件代码包含:

The form_load event code contains:

Dim AnItemObj As New ItemInfo

然后是一个包含以下内容的循环:

Then a loop that includes:

AnItemObj.ItemNo = AFile.RecordId
AnItemObj.ItemType = temp
AlList.Add(AnItemObj)

所以我现在应该有这些对象的 ArrayList，但是如果我尝试检索数据:

So I should now have an ArrayList of these objects, however if I try to retrieve the data:

MsgBox(AlList(5).ItemNo)

我总是得到列表中最后一个值的 ItemNo.

I always get the ItemNo of the last value in the list.

我错过了什么?

推荐答案

放入如下代码:

Dim AnItemObj As New ItemInfo

inside 将 AnItemObj 添加到列表的循环.

inside the loop which adds AnItemObj to the list.

当您向列表添加引用类型时，您只是添加了引用，而不是值.

When you add a reference type to a list, you are only adding the reference, not the value.

这意味着如果您将 10 次相同的实例添加到列表中，它将向列表添加 10 次相同的引用.但是如果之后你仍然有这个实例的引用，你可以修改它的属性，因为列表中的所有 10 个条目都指向内存中的同一个引用，所有 10 个条目都将被修改.

This means that if you add 10 times the same instance to a list, it will add 10 times the same reference to the list. But if afterward you still have a reference to this instance you can modify its properties and as all 10 entries in the list point to the same reference in memory, all 10 entries will be modified.

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