我正在为许多自定义控件开发Generic Undoclass，并且在尝试为多选列表框实现撤消时遇到困难。
撤消类：
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
和一些撤消代码。在自定义Listbox类中，我添加了：
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)
....
我遇到的问题是传递的＆＃34;项目＆＃34;没有公开与原始SelectedIndices属性相同的属性，因此CurrentValue.equals（item）测试总是失败。尽管vs helpfile明确指出selectedIndices是一个＆＃34; ListBox.SelectedIndexCollection，其中包含控件中当前所选项的索引＆＃34;我这样做的方式不起作用（它适用于我所有的其他控件，我只是将它们的.text值作为字符串传递或.Checked值作为布尔等...）。
我做错了什么？
答案 0 :(得分：0)
我想我找到了一种方法来解决它（只是一个测试例程，因此我使用函数返回测试信息而不是方法和短变量名称）：
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
我必须遍历'add'例程中的列表，因为相等运算符会创建对当前值的引用而不是复制内容
测试代码：
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)
输出：
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!
接下来，当selectedItem或SelectedValue作为基本变量传递时，我打算基于gettype.IsgenericType拆分操作。