Listbox SelectedIndexCollection與SelectedIndices

Question

我正在爲一些自定義控件創建泛型Undoclass，並在嘗試實現多選列表框的撤消時陷入困境。

撤消類別：

Public Class UndoClass(Of T) 
    Private FirstValue As T 
    Private PrevValue As T 
    Private CurrentValue As T 
    Private HasValue As Boolean 
    Public Sub Add(ByVal Item As T) 
     If Not HasValue Then 
      FirstValue = Item 
      PrevValue = Item 
      HasValue = True 
     ElseIf Not CurrentValue.Equals(Item) Then 
      If Not CurrentValue.Equals(FirstValue) Then PrevValue = CurrentValue 
     End If 
     CurrentValue = Item 
    End Sub 

和一些撤銷代碼。在自定義列表框類我說：

dim undoing as new UndoClass(Of SelectedIndexCollection) 

Protected Overrides Sub OnEnter(e As EventArgs) 
    undoing.add(me.SelectedIndices) 
    .... 
Protected Overrides Sub OnSelectedIndexChanged(e As EventArgs) 
    if me.SelectedIndex>=0 then undoing.add(me.selectedIndices) 
    .... 

我遇到的問題是，通過「項目」，沒有相同的屬性作爲源將selectedIndices屬性，因此CurrentValue.equals（項目）測試總是失敗。儘管vs helpfile明確指出selectedIndices是一個「ListBox.SelectedIndexCollection，它包含了控件中當前選定項目的索引」，但我這樣做的方式並不起作用（它適用於所有其他控件，我只是通過它們的.text值作爲字符串或.Checked值作爲布爾等...）。

我做錯了什麼？

Answer 1

我想我找到了一種方法來解決它（只是一個測試程序，所以我用函數返回的測試信息，而不是方法和短變量名）：

Public Class TestListClass(Of T) 
    Dim Current As New List(Of T) 
    Dim Prev As New List(Of T) 
    Public Function add(T1 As List(Of T)) As String 
     Dim s As String = String.Empty 
     If T1.GetType.IsGenericType Then ' better safe then sorry and we'll need that in the final version 
      Dim ar As Type() = T1.GetType.GenericTypeArguments 
      s = ar(0).ToString 
     End If 
     If Current.Count = 0 Then 
      For Each X As T In T1 
       Current.Add(X) 
      Next 
      Return "created " & s & vbNewLine 
     Else 
      If Prev.Count > 0 Then Prev.Clear() 
       For Each X As T In Current 
        Prev.Add(X) 
       Next 
       Current.Clear() 
       For Each X As T In T1 
        Current.Add(X) 
       Next 
       Return "pushed " & s & vbNewLine 
      End If 
     End Function 
     Public Function Listing() As String 
      Dim S As String = String.Empty 
      If Prev.Count > 0 Then 
       S &= "Prev= " & Enumerate(Prev) & vbNewLine 
      End If 
      If Current.Count > 0 Then 
       S &= "Current= " & Enumerate(Current) & vbNewLine 
      End If 
      Return S 
     End Function 
     Private Function Enumerate(T1 As List(Of T)) As String 
      Dim s As String = String.Empty 
      For I = 0 To T1.Count - 1 
       s &= T1.Item(I).ToString & csComa 
      Next 
      Return s 
     End Function 
Public Function Compare(T1 As List(Of T)) As String 
    Dim s As String = Enumerate(T1) 
    If ListsSame(Current, T1) Then 
     s &= "is same as current! (" & Enumerate(Current) & ")" 
    ElseIf ListsSame(Prev, T1) Then 
     s &= "is same as Previous! (" & Enumerate(Prev) & ")" 
    Else 
     s &= "does not match!" 
    End If 
    Return s & vbNewLine 
End Function 
    Private Function ListsSame(T1 As List(Of T), T2 As List(Of T)) As Boolean 
     Dim ok As Boolean = False 
     If T1.Count > T2.Count Then 
      ok = T1.Except(T2).Any 
     Else 
      ok = T2.Except(T1).Any 
     End If 
     Return Not ok 
    End Function 
End Class 

我不得不通過在列表進行迭代「添加」例程作爲平等操作者將創建到的電流值的參考，而不是複製內容

測試代碼：

Dim t1 As New TestListClass(Of Integer), l1 As New List(Of Integer), t2 As New TestListClass(Of String), l2 As New List(Of String) 
Dim x1() As Integer = {1, 2, 3, 4, 5} 
l1.AddRange(x1) 
Me.txtResult.Text = t1.add(l1) 
Dim y1() As Integer = {6, 7, 8} 
Dim l11 As New List(Of Integer) 
l11.AddRange(y1) 
Me.txtResult.Text &= t1.add(l11) 
Me.txtResult.Text &= t1.Listing 
Me.txtResult.Text &= t1.Compare(l1) 
Me.txtResult.Text &= t1.Compare(l11) 
l11.Add(9) 
Me.txtResult.Text &= t1.Compare(l11) 
Dim x2() As String = {"10", "20", "30"} 
l2.AddRange(x2) 
Me.txtResult.Text &= t2.add(l2) 
Dim y2() As String = {"a", "b", "c"} 
Dim l22 As New List(Of String) 
l22.AddRange(y2) 
Me.txtResult.Text &= t2.add(l22) 
Me.txtResult.Text &= t2.Listing 
Me.txtResult.Text &= t2.Compare(l2) 
Me.txtResult.Text &= t2.Compare(l22) 
l22.Add("d") 
Me.txtResult.Text &= t2.Compare(l22) 

輸出：

created System.Int32 
pushed System.Int32 
Prev= 1, 2, 3, 4, 5, 
Current= 6, 7, 8, 
1, 2, 3, 4, 5, is same as Previous! (1, 2, 3, 4, 5,) 
6, 7, 8, is same as current! (6, 7, 8,) 
6, 7, 8, 9, does not match! 
created System.String 
pushed System.String 
Prev= 10, 20, 30, 
Current= a, b, c, 
10, 20, 30, is same as Previous! (10, 20, 30,) 
a, b, c, is same as current! (a, b, c,) 
a, b, c, d, does not match! 

接着我打算當將selectedItem或的SelectedValue作爲基本變量被傳遞到分割基於gettype.IsgenericType的操作。