VB.net 对象数组抛出异常

Question

运行以下代码时出现异常。

Public Function getSongs() As Song()
   ' Dim dir As New DirectoryInfo(Application.ExecutablePath)
     Dim dir As New DirectoryInfo(directory)
     Dim songsInDir() As Song = Nothing
     Dim i As Integer = 0
     For Each file As FileInfo In dir.GetFiles()
        'only read ".mp3" files
        If file.Extension = ".mp3" Then
            songsInDir(i) = New Song(file.Name)
            i = +i
        End If
    Next
    Return songsInDir
End Function

我在网上遇到错误：

songsInDir(i) = New Song(file.Name)

我得到一个未捕获的异常，它说：

“对象引用未设置为对象的实例。”

歌曲对象有一个：

Public Sub new(By Val filename as String)

... 设置变量并检索文件信息的子程序（此代码有效）

任何帮助将不胜感激！

Answer 1

尝试使用列表：

Public Function getSongs() As Song()
  Dim dir As New DirectoryInfo(directory)
  Dim songsInDir() As New List(of Song)
  For Each file As FileInfo In dir.GetFiles()
    'only read ".mp3" files
    If file.Extension = ".mp3" Then
      songsInDir.Add(New Song(file.Name)
    End If
  Next
  Return songsInDir.ToArray()
End Function

Answer 2

您的问题是数组在初始化时需要一个大小，并将其设置为 Nothing 可以让您完全做到这一点。给数组一个大小，不要将其设置为 Nothing。此外，还有一种更清洁的方法。

Public Function getSongs() As Song()
    Dim songFiles As String() = Directory.GetFiles(directory, "*.mp3")
    Dim songsInDir(songFiles.Length) As Song
    Dim i As Integer = 0
    For Each file As String In songFiles
        songsInDir(i) = New Song(Path.GetFileName(file))
        i = +i
    Next
    Return songsInDir
End Function 

Answer 3

你应该指定数组大小

Dim i as Integer = dir.GetFiles().count 或 dir.FilesCount()

Dim songInDir(i) As Song = Nothing

或者你可以使用动态数组

将这一行放在你的 for 循环中

ReDim Preserve songInDir(i)