VB.NET：通过将处理程序函数指定为变量来实现“AddHandler”

Question

我正在为 Autodesk Inventor（一个 3D CAD 程序）编写一个插件。该插件向 Inventor 添加了一系列内部命令，并为每个命令创建了一个工具栏按钮。我需要将每个命令的 Execute 事件连接到加载项中的处理程序函数。

我创建了一个“MyCommand”类，其中包含定义命令所需的所有信息。我还创建了一个 List(Of MyCommand) ，其中包含每个命令的定义。最后，我可以遍历每个命令并创建内部 Inventor 命令定义，以及将按钮添加到工具栏。但是，我不知道该怎么做是将命令与其 Handler 函数在 loop 内关联起来。

下面的示例代码说明了我所追求的：

Sub CreateCommands()
    Dim oCommands As New List(Of MyCommand)

    oCommands.Add(New MyCommand("DrawLogoCmd", "Draw Logo", "DrawLogoSub"))
    oCommands.Add(New MyCommand("PublishDrawingCmd", "Publish Drawing", "PublishDrawingSub"))
    ' [Dozens more commands]

    For Each oCommand As MyCommand In oCommands
        ' Code for adding internal command definition and button to Inventor. This is working fine.
        Dim oCommandDef As Inventor.CommandDefinition = InventorApp.CommandDefinitions.Add(oCommand.InternalDefinitionName, oCommand.DisplayName)
        InventorApp.ToolbarButtons.Add(oCommandDef)

        ' Associate command definition with handler function
        ' ===== THIS IS THE LINE I NEED TO FIGURE OUT =====
        AddHandler oCommandDef.OnExecute, AddressOf oCommand.HandlerSubName
    Next
End Sub

Sub DrawLogoSub()
    ' [My add-in's code to draw logo in Inventor]
End Sub

Sub PublishDrawingSub()
    ' [My add-in's code to publish drawing in Inventor]
End Sub

Class MyCommand
    Public InternalDefinitionName As String
    Public DisplayName As String
    Public HandlerSubName As String

    Sub New(InternalDefinitionName As String, DisplayName As String, HandlerSubName As String)
        With Me
            .InternalDefinitionName = InternalDefinitionName
            .DisplayName = DisplayName
            .HandlerSubName = HandlerSubName
        End With
    End Sub
End Class

那么，这可能吗？有什么方法可以使用其名称作为字符串来获取我的函数的“AddressOf”？或者，是否有某种方法可以在 MyCommand 类中存储对函数本身的引用，并将其传递给 AddressOf 运算符？

或者，除了“AddHandler/AddressOf”之外还有其他方法可以使用吗？

任何建议表示赞赏。

Answer 1

是的，您可以使用反射按名称找到该方法，但我不推荐它。该AddHandler命令通常给出的AddressOf一个方法，但它也可以采取委托，只要它符合事件的签名。所以，除非你有一些需要通过字符串来做，否则我建议你做这样的事情。假设事件匹配普通EventHandler委托：

Sub CreateCommands()
    Dim oCommands As New List(Of MyCommand)

    oCommands.Add(New MyCommand("DrawLogoCmd", "Draw Logo", AddressOf DrawLogo))
    oCommands.Add(New MyCommand("PublishDrawingCmd", "Publish Drawing", AddressOf PublishDrawing))
    ' [Dozens more commands]

    For Each oCommand As MyCommand In oCommands
        ' Code for adding internal command definition and button to Inventor. This is working fine.
        Dim oCommandDef As Inventor.CommandDefinition = InventorApp.CommandDefinitions.Add(oCommand.InternalDefinitionName, oCommand.DisplayName)
        InventorApp.ToolbarButtons.Add(oCommandDef)

        ' Associate command definition with handler function
        AddHandler oCommandDef.OnExecute, oCommand.Handler
    Next
End Sub

Sub DrawLogo(sender As Object, e As EventArgs)
    ' [My add-in's code to draw logo in Inventor]
End Sub

Sub PublishDrawing(sender As Object, e As EventArgs)
    ' [My add-in's code to publish drawing in Inventor]
End Sub

Class MyCommand
    Public InternalDefinitionName As String
    Public DisplayName As String
    Public Handler As EventHandler

    Sub New(InternalDefinitionName As String, DisplayName As String, Handler As EventHandler)
        With Me
            .InternalDefinitionName = InternalDefinitionName
            .DisplayName = DisplayName
            .Handler = Handler
        End With
    End Sub
End Class

如果你真的需要通过字符串来做，你可以使用这样的反射（请注意，我使用NameOf而不是将方法名称硬编码为字符串文字，只是为了使其更安全）：

Sub CreateCommands()
    Dim oCommands As New List(Of MyCommand)

    oCommands.Add(New MyCommand("DrawLogoCmd", "Draw Logo", NameOf(DrawLogo)))
    oCommands.Add(New MyCommand("PublishDrawingCmd", "Publish Drawing", NameOf(PublishDrawing)))
    ' [Dozens more commands]

    For Each oCommand As MyCommand In oCommands
        ' Code for adding internal command definition and button to Inventor. This is working fine.
        Dim oCommandDef As Inventor.CommandDefinition = InventorApp.CommandDefinitions.Add(oCommand.InternalDefinitionName, oCommand.DisplayName)
        InventorApp.ToolbarButtons.Add(oCommandDef)

        ' Associate command definition with handler function
        AddHandler oCommandDef.OnExecute, Sub(sender As Object, e As EventArgs) CallMethod(oCommand.Handler)
    Next
End Sub

Private Sub CallMethod(name As String)
    Me.GetType().GetMethod(name).Invoke(Me, Nothing)
End Sub

Sub DrawLogo()
    ' [My add-in's code to draw logo in Inventor]
End Sub

Sub PublishDrawing()
    ' [My add-in's code to publish drawing in Inventor]
End Sub