vb.net - VB / CLASS问题：所有记录仅显示最后一条记录

Question

我尝试获取每张专辑的歌曲列表。我创建了 2 个类：专辑和歌曲，所以我可以将它们组织如下：

Public Class Album
    Sub New()
        Entered = Now
    End Sub
    Public Entered As DateTime
    Public AlbumName As String = ""
    Public Artist As String = ""
    Public YearReleased As Integer = 1900
    Public Songs As New List(Of Song)
End Class

Public Class Song
    Public SongName As String = ""
    Public SongLength As String = ""
End Class

但是，当我将歌曲添加到专辑时，我总是得到最后一首输入的歌曲。这是一个输出结果的例子。

Protected Sub Test()
    Dim vAlbum As New Album
    Dim vsong As New Song

    vAlbum.AlbumName = "Test 01"
    vAlbum.Artist = "Jackie"
    vAlbum.YearReleased = 2012

    vsong.SongName = "Exit"
    vsong.SongLength = "1.5"
    vAlbum.Songs.Add(vsong)

    vsong.SongName = "Exit II"
    vsong.SongLength = "2.5"
    vAlbum.Songs.Add(vsong)

    For Each sSong As Song In vAlbum.Songs
        Response.Write(sSong.SongName + "<br>")
    Next
End Sub

输出 ：

出口二

出口二

我到处都有谷歌，但找不到所有歌曲的最新记录。

欢迎任何帮助。

谢谢，弗雷德

Answer 1

经典参考问题。您的 vsong 始终是同一个对象。您需要实例化一个新实例：

...
vAlbum.Songs.Add(vsong)
vsong = new Song()
vsong.SongName = "Exit II"
...

Answer 2

您添加了Song两次相同的内容，只是更改了它的字段。

你应该使用这样的东西：

Dim vAlbum As New Album

vAlbum.AlbumName = "Test 01"
vAlbum.Artist = "Jackie"
vAlbum.YearReleased = 2012

Dim vsong As New Song
vsong.SongName = "Exit"
vsong.SongLength = "1.5"
vAlbum.Songs.Add(vsong)

vsong As New Song ' create a new instance of Song
vsong.SongName = "Exit II"
vsong.SongLength = "2.5"
vAlbum.Songs.Add(vsong)

或者更好的是，使用对象初始化器或创建一个接受所有必要值的构造器：

Public Class Song

    Public SongName As String = ""
    Public SongLength As String = ""

    Public Sub new(name as String, length as String)
        SongName = name
        SongLength = length
    End Sub

End Class

...

vAlbum.Songs.Add(new Song("Exit", "1.5"))
vAlbum.Songs.Add(new Song("Exit II", "2.5"))