如何对结构数组进行排序？答案

【问题标题】：How can I sort an array of a structure?如何对结构数组进行排序？
【发布时间】：2015-09-25 23:24:55
【问题描述】：

我有一个结构数组。它是这样声明的

Public SongsList as New List(Of Song)

“歌曲”是结构的名称。它有 2 个变量：路径和名称；我想知道如何按名称对这个数组进行排序。

Public Structure Song
  Public Path as String
  Public Name as String
End Structure

我试过了

ListBox1.Items.Clear()
Dim sorted = SongsList.OrderBy(Function(s) s.Name).ToList 
Dim i As Integer 
For i = 0 To sorted.Count - 1
    ListBox1.Items.Add(sorted(i).Name.ToString) 
Next

但它会抛出一个NullReferenceException。

这就是我向 SongsList 添加项目的方式

Dim open As New OpenFileDialog
open.Title = "Add songs"
open.Filter = "MP3 Files(*.mp3)|*.mp3"
open.Multiselect = True
ListBox1.Items.Clear()
If open.ShowDialog = DialogResult.OK Then
    For Each SelectedSong As String In open.FileNames
        i += 1
        Dim songToAdd As New Song
        songToAdd.Path = SelectedSong.ToString
        songToAdd.Name = GetSafeFileName(SelectedSong.ToString)
        SongsList.Add(songToAdd)
        ListBox1.Items.Add(SongsList(i).Path)
    Next
End If

【问题讨论】：

我编辑了您的问题以包含您在 OneFineDay 答案的 cmets 中提到的代码；但请下次尝试包含您尝试过的代码 - 即使它不起作用。现在，你能告诉我们你是如何填写SongsList的吗？
为什么对已经是字符串的变量调用.ToString？
What is a NullReferenceException and how do I fix it? 的副本

标签： arrays vb.net list sorting

【解决方案1】：

您可以使用 Lambda 表达式。它使用您在OrderBy 函数中选择的字段。让我们重写ToString 方法来告诉列表框要显示什么，然后您可以将列表设置为数据源。

班级：

Public Class Song
  Public Property Path as String
  Public Property Name as String
  Public Overrides Function ToString() As String
    Return Me.Path
  End If
End Class

用法：

Dim open As New OpenFileDialog
open.Title = "Add songs"
open.Filter = "MP3 Files(*.mp3)|*.mp3"
open.Multiselect = True
If open.ShowDialog = DialogResult.OK Then
  For Each SelectedSong As String In open.FileNames
    Dim songToAdd As New Song
    songToAdd.Path = SelectedSong
    songToAdd.Name = GetSafeFileName(SelectedSong.ToString)
    SongsList.Add(songToAdd)
   Next
End If
Listbox1.DataSource = SongsList.OrderBy(Function(s) s.Name).ToList

【讨论】：

我试过了，但没有用。这是代码： ListBox1.Items.Clear() Dim sorted = SongsList.OrderBy(Function(s) s.SongName).ToList Dim i As Integer For i = 0 To sorted.Count - 1 ListBox1.Items.Add(sorted (i).SongName.ToString) 下一个
NullReferenceException
您在上面写道，结构中是Name，而不是SongName。是哪一个？
没关系。我已经重写了代码，但我忘记了。对不起。使用“名称”。
是的。每次我运行程序都会清除的列表。

【解决方案2】：

*与 OneFineDay 的回答非常相似...

您不需要自定义类，只需使用List(Of FileInfo)：

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim open As New OpenFileDialog
    open.Title = "Add songs"
    open.Filter = "MP3 Files(*.mp3)|*.mp3"
    open.Multiselect = True
    If open.ShowDialog = DialogResult.OK Then
        ListBox1.DataSource = Nothing
        Dim songs As New List(Of FileInfo)
        For Each SelectedSong As String In open.FileNames
            songs.Add(New FileInfo(SelectedSong))
        Next
        songs = songs.OrderBy(Function(fi) fi.Name).ToList
        ListBox1.DataSource = songs
        ListBox1.DisplayMember = "Name"
        ListBox1.ValueMember = "FullName"
    End If
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    If ListBox1.SelectedIndex <> -1 Then
        Dim fi As FileInfo = DirectCast(ListBox1.SelectedItem, FileInfo)
        Dim name As String = fi.Name
        Dim fullPath As String = fi.FullName
        Debug.Print("name = " & name)
        Debug.Print("fullPath = " & fullPath)
    End If
End Sub

【讨论】：