C# ActionCommand:ICommand 到 VB.net 的翻译

Question

我找到了一个 C# 类 ActionCommand，它实现了 ICommand 并基于 Execute 和 CanExecute 的委托。到目前为止对我来说看起来很完美。

  public class ActionCommand : ICommand
  {
    private readonly Action<object> _executeHandler;
    private readonly Func<object, bool> _canExecuteHandler;

    public ActionCommand(Action<object> execute, Func<object, bool> canExecute)
    {
      if (execute == null)
        throw new ArgumentNullException("Execute cannot be null");
      _executeHandler = execute;
      _canExecuteHandler = canExecute;
    }

    public event EventHandler CanExecuteChanged
    {
      add { CommandManager.RequerySuggested += value; }
      remove { CommandManager.RequerySuggested -= value; }
    }
    public void Execute(object parameter)
    {
      _executeHandler(parameter);
    }
    public bool CanExecute(object parameter)
    {
      if (_canExecuteHandler == null)
        return true;
      return _canExecuteHandler(parameter);
    }
  }

现在我将其转换为我需要的 VB.net 变体（使用代码翻译器和一些实际操作）

Public Class ActionCommand
  Implements ICommand

  Public Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged

  Private ReadOnly _executeHandler As Action(Of Object)
  Private ReadOnly _canExecuteHandler As Func(Of Object, Boolean)

  Public Sub New(ByVal execute As Action(Of Object),
                 ByVal canExecute As Func(Of Object, Boolean))
    If execute Is Nothing Then
      Throw New ArgumentNullException("Execute cannot be null")
    End If
    _executeHandler = execute
    _canExecuteHandler = canExecute
  End Sub

  Public Sub Execute(ByVal parameter As Object) Implements ICommand.Execute
    _executeHandler(parameter)
  End Sub

  Public Function CanExecute(ByVal parameter As Object) As Boolean Implements ICommand.CanExecute
    If (_canExecuteHandler Is Nothing) Then
      Return True
    End If
    Return _canExecuteHandler(parameter)
  End Function
End Class

我的问题是 CanExecuteChanged 以及将事件从 CommandManager.RequerySuggested 注册/映射到 CanExecuteChanged。在线代码翻译器建议如下：

Public Custom Event CanExecuteChanged As EventHandler
    AddHandler(ByVal value As EventHandler)
        CommandManager.RequerySuggested += value
    End AddHandler
    RemoveHandler(ByVal value As EventHandler)
        CommandManager.RequerySuggested -= value
    End RemoveHandler
End Event

但这不能满足 ICommand.CanExecuteChanged 有人可以帮忙翻译或解决这个问题吗？

Answer 1

Public Custom Event CanExecuteChanged As EventHandler
    AddHandler(ByVal value As EventHandler)
        AddHandler CommandManager.RequerySuggested, value
    End AddHandler
    RemoveHandler(ByVal value As EventHandler)
        RemoveHandler CommandManager.RequerySuggested, value
    End RemoveHandler
End Event

Answer 2

我认为您正在寻找的更像是：

    Public Custom Event CanExecuteChanged As EventHandler _
                   Implements ICommand.CanExecuteChanged
        AddHandler(ByVal value As EventHandler)
            AddHandler CommandManager.RequerySuggested, value
        End AddHandler

        RemoveHandler(ByVal value As EventHandler)
            RemoveHandler CommandManager.RequerySuggested, value
        End RemoveHandler

        RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
            CanExecute(sender)
        End RaiseEvent
    End Event

Answer 3

本文来自 MALIGUI .NET 博客 可能会有所帮助：

Public Custom Event CanExecuteChanged As EventHandler _
    Implements ICommand.CanExecuteChanged
        AddHandler(ByVal value As EventHandler)
            Dim handler2 As EventHandler
            Dim canExecuteCommand = __CanExecuteCommand
            Do
                handler2 = canExecuteCommand
                Dim handler3 = DirectCast(System.Delegate.Combine(handler2, value), EventHandler)
                canExecuteCommand = Interlocked.CompareExchange((__CanExecuteCommand), handler3, handler2)
            Loop While (Not canExecuteCommand Is handler2)
            __CanExecuteCommand = canExecuteCommand
        End AddHandler
        RemoveHandler(ByVal value As EventHandler)
            Dim handler2 As EventHandler
            Dim canExecuteCommand = __CanExecuteCommand
            Do
                handler2 = canExecuteCommand
                Dim handler3 = DirectCast(System.Delegate.Remove(handler2, value), EventHandler)
                canExecuteCommand = Interlocked.CompareExchange((__CanExecuteCommand), handler3, handler2)
            Loop While (Not canExecuteCommand Is handler2)
            __CanExecuteCommand = canExecuteCommand
        End RemoveHandler
        RaiseEvent(ByVal sender As Object, ByVal e As EventArgs)
            If (__CanExecuteCommand IsNot Nothing) Then
                __CanExecuteCommand.Invoke(sender, e)
            End If
        End RaiseEvent
    End Event