VB.NET 中的 WPF AttachedCommandsBehavior

Question

谁能给我一个如何实现 AttachedCommands 的例子？

C# 中有一些示例，我认为它与 C# 非常相似，但我在将代码转换为 VB.NET 时遇到了问题。

目前我尝试将 C# AttachedCommand-Class 转换为 VB.net 看起来像这样:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports System.Windows
Imports System.Windows.Input
Imports System.Reflection

Public Class AttachedCommand
    Inherits DependencyObject

#Region "CommandParameter-Class"

    Private NotInheritable Class CommandParameter

    Public Shared ReadOnly Property DefaultCP() As CommandParameter
        Get
            Return New CommandParameter()
        End Get
    End Property



    Private _command As ICommand
    Public Property Command() As ICommand
        Get
            Return _command
        End Get
        Set(ByVal value As ICommand)
            _command = value
        End Set
    End Property


    Private _eventName As String
    Public Property EventName() As String
        Get
            Return _eventName
        End Get
        Set(ByVal value As String)
            _eventName = value
        End Set
    End Property


    Private _callBack As [Delegate]
    Public Property Callback() As [Delegate]
        Get
            Return _callBack
        End Get
        Set(ByVal value As [Delegate])
            _callBack = value
        End Set
    End Property

End Class

#End Region

#Region "Properties"

Private Shared _parameter As IDictionary(Of DependencyObject, CommandParameter)
Private Shared Property Parameter() As IDictionary(Of DependencyObject, CommandParameter)
    Get
        Return _parameter
    End Get
    Set(ByVal value As IDictionary(Of DependencyObject, CommandParameter))
        _parameter = value
    End Set
End Property




Public Property Command() As ICommand
    Get
        Return GetValue(CommandProperty)
    End Get

    Set(ByVal value As ICommand)
        SetValue(CommandProperty, value)
    End Set
End Property

Public Shared ReadOnly CommandProperty As DependencyProperty = _
                       DependencyProperty.Register("Command", _
                       GetType(ICommand), GetType(AttachedCommand), _
                       New UIPropertyMetadata(AddressOf CommandChanged))

Public Property EventName() As String
    Get
        Return GetValue(EventNameProperty)
    End Get

    Set(ByVal value As String)
        SetValue(EventNameProperty, value)
    End Set
End Property

Public Shared ReadOnly EventNameProperty As DependencyProperty = _
                       DependencyProperty.Register("EventName", _
                       GetType(String), GetType(AttachedCommand), _
                       New UIPropertyMetadata(AddressOf EventNameChanged))


#End Region

#Region "Event-Handler"

Public Shared Sub CommandChanged(ByVal dependencyObject As DependencyObject, ByVal args As DependencyPropertyChangedEventArgs)
    If Not Parameter.ContainsKey(dependencyObject) Then
        Parameter.Add(dependencyObject, CommandParameter.DefaultCP)
    End If

    If (Not Parameter(dependencyObject).Callback = Nothing) AndAlso (Not args.OldValue = Nothing) Then
        _RemoveEventHandler(dependencyObject)
    End If

    Parameter(dependencyObject).Command = CType(args.NewValue, ICommand)

    _AttachEventHandler(dependencyObject)

End Sub

Public Shared Sub EventNameChanged(ByVal dependencyObject As DependencyObject, ByVal args As DependencyPropertyChangedEventArgs)
    If Not Parameter.ContainsKey(dependencyObject) Then
        Parameter.Add(dependencyObject, CommandParameter.DefaultCP)
    End If
End Sub

#End Region


#Region "Helper"

Private Shared Sub _RemoveEventHandler(ByVal dependencyObject As DependencyObject)
    If dependencyObject Is Nothing Then
        Throw New ArgumentNullException("DependencyObject is null.")
    End If

    If Not Parameter.ContainsKey(dependencyObject) Then
        Exit Sub
    End If

    Dim param As CommandParameter = Parameter(dependencyObject)

    If param.Callback Is Nothing Then
        Throw New InvalidProgramException("Cannot remove Callback. Callback is null.")
    End If

    Dim eventInfo As EventInfo = dependencyObject.GetType().GetEvent(param.EventName)
    If eventInfo Is Nothing Then
        Throw New InvalidProgramException(String.Format("Cannot find an event with the name <{0}>", param.EventName))
    End If

    eventInfo.RemoveEventHandler(dependencyObject, param.Callback)

End Sub

Private Shared Sub _AttachEventHandler(ByVal dependencyObject)
    If dependencyObject Is Nothing Then
        Throw New ArgumentNullException("DependencyObject is null")
    End If

    If Not Parameter.ContainsKey(dependencyObject) Then
        Exit Sub
    End If

    Dim param As CommandParameter = Parameter(dependencyObject)

    If param.Command Is Nothing Or String.IsNullOrEmpty(param.EventName) Then
        Exit Sub
    End If

    Dim eventInfo As EventInfo = dependencyObject.GetType.GetEvent(param.EventName)
    If eventInfo Is Nothing Then
        Throw New InvalidProgramException(String.Format("Cannot find an event with the name <{0}>", param.EventName))
    End If



    eventInfo.AddEventHandler(dependencyObject, param.Callback)

End Sub

Private Shared Sub _CommandExecutAction(ByVal parameter As CommandParameter)
    parameter.Command.Execute(Nothing)
End Sub

Private Shared Function _CreateHandler(ByVal eventInfo As EventInfo, ByVal method As Action) As [Delegate]
    If eventInfo Is Nothing Then
        Throw New ArgumentNullException("EventInfo is null")
    End If

    If method Is Nothing Then
        Throw New ArgumentNullException("Action-method is null")
    End If

    Dim handlerType = eventInfo.EventHandlerType
    Dim eventParams = handlerType.GetMethod("Invoke").GetParameters()

    Dim parameters = eventParams.[Select](Function(p) System.Linq.Expressions.Expression.Parameter(p.ParameterType, "x"))
    Dim body = System.Linq.Expressions.Expression.[Call](System.Linq.Expressions.Expression.Constant(method), method.[GetType]().GetMethod("Invoke"))
    Dim lambda = System.Linq.Expressions.Expression.Lambda(body, parameters.ToArray())

    Return [Delegate].CreateDelegate(handlerType, lambda.Compile(), "Invoke", False)

End Function
#End Region

#Region "INIT"

Public Sub New()
    Parameter = New Dictionary(Of DependencyObject, CommandParameter)()
End Sub

#End Region

End Class

但现在我遇到了问题，GetValue() 和 SetValue() 方法不可用。有任何想法吗？

感谢您的帮助..

Answer 1

一个 AttachedCommandBehaviour只不过是一个 ICommand 类型的依赖属性，它 Hook 了一些事件。

查看 Dr. WPFs VB-snippets其中包括依赖属性的片段。

如果您使用包含属性更改处理程序的处理程序，则可以使用此处理程序来 Hook 您想要的事件。在事件处理程序中，您调用附加的命令。

如果您仍然无法使其工作，请发布一些代码。