VB.net對象數組拋出異常

Question

運行以下代碼時出現異常。

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 

我得到行錯誤：

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

我得到一個未捕獲的異常，說：「未將對象引用設置到對象的實例」

這首歌對象有：

Public Sub new(By Val filename as String) 

...子，設置一個變量，並獲取文件信息（此代碼）

任何幫助，將不勝感激！

Answer 1

嘗試使用列表：

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

應指定數組大小

昏暗i設定爲整數= dir.GetFiles（）。計數或dir.FilesCount（）

昏暗songsInDir（I）的樂曲=無

或您可以使用動態數組

，就把這行你在for循環

使用ReDim保留songsInDir（I）

Answer 3

你的問題是，數組需要一個規模時，他們正在初始化，將其設置爲沒有給你這一點。給數組一個大小，不要將它設置爲Nothing。此外，還有更簡潔的方法來做到這一點。

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