需要動態創建實現相同接口的對象（使用Activator.CreateInstance）

Question

我無法弄清楚這一點。我想傳入一個GenreID並獲得相應類型的對象列表，即如果我傳入MyGenre.RockAndRoll，我想要一個RockAndRoll對象列表。

公共枚舉MyGenre 替代= 0 rockAndRoll = 1個 國家= 2 結束枚舉

 Public Interface IGenre 
      Inherits IDisposable 
      Property title As String 
      Property artist As String 
      Property duration As Decimal 
      Property rating As Integer 
      Sub Listen() 
     End Interface 

     Public Class RockAndRoll 
      Implements IGenre 

      Public Property artist As String Implements IGenre.artist 

      Public Property duration As Decimal Implements IGenre.duration 

      Public Property rating As Integer Implements IGenre.rating 

      Public Property title As String Implements IGenre.title 

      Public Sub Listen() Implements IGenre.Listen 
       '... 
      End Sub 
#Region "IDisposable Support" 
'... 
#End Region 

     End Class 

     Public Class Country 
      Implements IGenre 

      Public Property artist As String Implements IGenre.artist 

      Public Property duration As Decimal Implements IGenre.duration 

      Public Property rating As Integer Implements IGenre.rating 

      Public Property title As String Implements IGenre.title 

      Public Sub Listen() Implements IGenre.Listen 
       '... 
      End Sub 
#Region "IDisposable Support" 
    '... 
#End Region 

     End Class 


     Public Function GetAlternativeList() As IEnumerable(Of IGenre) 
      Return GetIGenreList(MyGenre.alternative) 
     End Function 

     Public Function GetrockAndRollList() As IEnumerable(Of IGenre) 
      Return GetIGenreList(MyGenre.alternative) 
     End Function 

     Public Function GetIGenreList(p_MyGenre As MyGenre) As IEnumerable(Of IGenre) 
      Using db As New OracleDataContext 
       Return (From s In db.SongList 
         Where s.Genre= MyGenre _ 
         Select CType(Activator.CreateInstance(p_MyGenre.GetGenreType, 
                   New With {.title = s.title, .artist = p1.artist, etc etc etc}), p_MyGenre.GetGenreTyp)).ToList 
      End Using 
     End Function 


     <Extension()> _ 
     Private Function GetGenreType(p_formatID As MyGenre) As Type 
      Select Case p_formatID 
       Case MyGenre.rockAndRoll 
        Return GetType(RockAndRoll) 
       Case MyGenre.country 
        Return GetType(PlayawayView) 
       Case Else 
        Return Nothing 
      End Select 
     End Function 

＃

EDIT

＃

我想添加爲了清楚另外的實例。第一個令人困惑。讓我們從格式的角度來看這個。

我想返回一個產品列表（DVD，CD，藍光等），每種格式都有它自己的內部類（用於藝術品大小，處理，合法性原因等）。

Class CD -> Implments IProduct 
Class DVD -> Implements IProduct 
Class BLURAY -> Implements IProduct 

i.e. dim MyList = (from p in MyProductTable select p).tolist 


returns 4 records. 
(0) 
    title: Motown Unmixed 
    artist: Various 
    duration: 36:25 
    format: CD 
    upc: 024543246157 
(1) 
    title: Classical Bytes - Bach 
    artist: Various 
    duration: 54:32 
    format: CD 
    upc: 709387901743 
(2) 
    title: Star Wars: Episode VI - Return of the Jedi 
    artist: null 
    duration: 136.00 
    format: DVD 
    upc: 883928446172 
(3) 
    title: Perfect Stranger 
    artist: null 
    duration: 95.36 
    format: BLU 
    upc: 043215190627 

我想要的是一個列表IPRODUCT。這可以通過點擊數據庫3次（對於每種格式類型）來完成。並將結果附加到IPRODUCT列表中。

dim MyProductList as new List(of IProduct) 

MyProductList.addrange((from p in MyProductTable where p.format = "CD" select new CD with {.title = p.title, etc etc etc}).tolist) 

MyProductList.addrange((from p in MyProductTable where p.format = "DVD" select new DVD with {.title = p.title, etc etc etc}).tolist) 

MyProductList.addrange((from p in MyProductTable where p.format = "BLU" select new BLURAY with {.title = p.title, etc etc etc}).tolist) 

我想將上面的3個查詢合併爲一個查詢。該查詢將返回CD，DVD和BLURAY對象的列表。

Answer 1

我更簡單的方法是將接口放在一邊，然後製作一個類型類型的枚舉，然後您只需要一個類來選擇每個類的類型。

Dim query = db.Songlist.Where(Function(s) s.genre = genre).ToList