vb.net对象数组丢失值-处理对象的集合

Question

我希望下面是完整的代码。

Q1：为什么两次调试写入产生不同的值？

第一个Debug Write可以正确执行，但是第二个Debug Write显示数组中的每个对象与在For Each循环中创建的最后一个对象具有相同的值。

问题2：除了数组以外，还有更好的方法来处理对象集合吗？

最后的测试值。

谢谢你的帮助。

码：

Public Class Form1

    Public facilities() As Facility


    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        Dim FileToImport As String = GetFileName("Select Facility Import File")
        Dim facility As New Facility
        Dim counter As Integer = 0
        Dim words() As String
        Dim i As Integer

        'Sample line format: FacID<TAB>FacSingleChar<TAB>ParentFacID

        Try
            If File.Exists(FileToImport) Then

                For Each line As String In File.ReadLines(FileToImport)

                    words = line.Split(vbTab)

                    With facility
                        .FacilityID = words(0)
                        .FacilitySingleCharID = words(1)
                        .ParentFacilityID = words(2)
                    End With

                    ReDim Preserve facilities(counter)

                    facilities(counter) = facility

                    Debug.WriteLine("First Print: " & facilities(i).FacilityID & vbTab & facilities(i).ParentFacilityID & facilities(i).FacilitySingleCharID)

                    counter = counter + 1

                Next line


                For i = 1 To facilities.GetUpperBound(0)

                    Debug.WriteLine("Second Print: " & facilities(i).FacilityID & vbTab & facilities(i).ParentFacilityID & facilities(i).FacilitySingleCharID)

                Next

            End If

        Catch ex As Exception

            MsgBox(ex.Message & vbTab & ex.ToString)

        End Try


    End Sub

    Private Function GetFileName(ByVal DialogTitle As String, Optional ByVal FileFilter As String = "All Files (*.*)|*.*") As String

        Dim oDlg As New OpenFileDialog()
        Dim FileName As String = ""

        Try

            With oDlg
                .Title = DialogTitle
                .Filter = FileFilter
                .ShowDialog()
                FileName = .FileName
            End With

            Return FileName

        Catch ex As Exception

            Return ""

        End Try

    End Function
End Class

Public Class Facility


    Private m_FacilityID As String = Space(4)
    Private m_ParentFacilityID As String = Space(4)
    Private m_FacilitySingleCharID As String = Space(1)


    Public Property FacilityID As String
        Get
            Return m_FacilityID
        End Get
        Set(ByVal value As String)
            m_FacilityID = value.PadRight(4)

        End Set
    End Property

    Public Property ParentFacilityID As String
        Get
            Return m_ParentFacilityID
        End Get
        Set(ByVal value As String)
            m_ParentFacilityID = value.PadRight(4)
        End Set
    End Property

    Public Property FacilitySingleCharID As String
        Get
            Return m_FacilitySingleCharID
        End Get
        Set(ByVal value As String)
            If Len(value) = 1 Then
                m_FacilitySingleCharID = value
            Else
                m_FacilitySingleCharID = "?"
            End If
        End Set
    End Property


End Class

导入文件的测试数据：

导入文件应具有3个制表符分隔的列：

（条目之间不应有空格，这是使它们在此处可读的唯一方法）

APC A NCT

BAB B NCT

BABG C NCT

CCR D NCT

Answer 1

这里有几个问题在起作用。

最直接的是在第二个打印循环中，For..Next循环索引变量i以1作为起始值，应为0。

第二个比较复杂。

您将创建一个新的设施对象，并且每次循环都要为该对象分配新的值，并将该对象分配给数组中新创建的最后一个元素。

问题在于对象如何工作以及如何使用它们

每次循环时，您只需将新值分配给同一对象，然后将该对象存储在数组的每个元素中。 但是，代码在后台执行的操作并不是每次都使用新值存储新对象，而是在每个元素中存储对同一对象的引用，并在每次循环中更改值。 这就是为什么数组中所有值都相同的原因。

您需要做的就是移动生产线

Dim facility As New Facility

进入循环，以便在每次通过循环时创建一个新对象

像这样

For Each line As String In File.ReadLines(FileToImport)
    Dim facility As New Facility
    words = line.Split(vbTab.ToCharArray)
    With facility
       .FacilityID = words(0)
       .FacilitySingleCharID = words(1)
       .ParentFacilityID = words(2)
    End With
    ReDim Preserve facilities(counter)
    facilities(counter) = facility
    Debug.WriteLine("First Print: " & facilities(counter).FacilityID & vbTab & facilities(counter).ParentFacilityID & facilities(counter).FacilitySingleCharID)
    counter = counter + 1
Next line

最初，对象可能会令人困惑，但请看一下引用类型和值类型以及变量范围。