71 lines
2.6 KiB
VB.net
71 lines
2.6 KiB
VB.net
Public Class MyVirtualizingElement(Of T As FrameworkElement)
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Inherits FrameworkElement
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Private Initializer As Func(Of T)
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Public Sub New(Initializer As Func(Of T))
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Me.Initializer = Initializer
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LazyLoadBehavior.OnFirstEnterScrollViewerViewport(Me, AddressOf Init)
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End Sub
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''' <summary>
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''' 实例化此控件。
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''' </summary>
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Public Function Init() As T
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Dim Element As T = Initializer()
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If Parent IsNot Nothing Then
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If TypeOf Parent IsNot Panel Then Throw New Exception("MyVirtualizingElement 的父级必须是一个 Panel")
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Dim ParentPanel As Panel = Parent
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Dim CurrentIndex As Integer = ParentPanel.Children.IndexOf(Me)
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ParentPanel.Children.RemoveAt(CurrentIndex)
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ParentPanel.Children.Insert(CurrentIndex, Element)
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End If
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Return Element
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End Function
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Public Shared Widening Operator CType(Virtualized As MyVirtualizingElement(Of T)) As T
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Return Virtualized.Init()
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End Operator
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End Class
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'非泛型形式
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Public Class MyVirtualizingElement
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Inherits FrameworkElement
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Private Initializer As Func(Of FrameworkElement)
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Public Sub New(Initializer As Func(Of FrameworkElement))
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Me.Initializer = Initializer
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LazyLoadBehavior.OnFirstEnterScrollViewerViewport(Me, AddressOf Init)
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End Sub
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''' <summary>
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''' 实例化此控件。
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''' </summary>
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Public Function Init() As FrameworkElement
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Dim Element As FrameworkElement = Initializer()
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If Parent IsNot Nothing Then
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If TypeOf Parent IsNot Panel Then Throw New Exception("MyVirtualizingElement 的父级必须是一个 Panel")
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Dim ParentPanel As Panel = Parent
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Dim CurrentIndex As Integer = ParentPanel.Children.IndexOf(Me)
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ParentPanel.Children.RemoveAt(CurrentIndex)
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ParentPanel.Children.Insert(CurrentIndex, Element)
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End If
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Return Element
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End Function
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''' <summary>
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''' 获取实例化后的控件。
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''' 如果该控件没有实例化，则会立即实例化。
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''' 如果类型错误，则返回原值。
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''' </summary>
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Public Shared Function TryInit(Element As FrameworkElement) As FrameworkElement
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If GetType(MyVirtualizingElement(Of )).IsInstanceOfGenericType(Element) Then
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Return CType(Element, Object).Init()
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ElseIf TypeOf Element Is MyVirtualizingElement Then
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Return CType(Element, MyVirtualizingElement).Init()
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Else
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Return Element
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End If
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End Function
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End Class
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