如何为AddressOf CalledBack添加代表？

Question

尝试添加一个代理...unsuccesfully。

   Public Function CallbackAddress() As Integer
  'UPGRADE_WARNING: Add a delegate for AddressOf CalledBack Click for more: 'ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?keyword="E9E157F7-EF0C-4016-87B7-7D7FBBC6EE08"'
    CallbackAddress = GetAddress(AddressOf CalledBack)
    End Function

    Private Function GetAddress(ByVal address As Integer) As Integer
        'GetAddress = address
        Return address
    End Function

以下是添加委托的失败(不完全或完全错误)尝试：

  Public Delegate Sub CalledBackDelegate(ByVal param As Integer)

  Public Function CallbackAddress() As Integer
        Dim myCalledBackDelegate As CalledBackDelegate = New CalledBackDelegate(AddressOf CalledBack)
        CallbackAddress = GetAddress(myCalledBackDelegate)  // << This doesn't work! 
    End Function

仍然有一个错误：

myCalledbackDegate不能转换为整数。

我遗漏了什么？

Answer 1

这三个提议的函数都是返回整数的函数。当然，虽然有一个返回委托的函数是可能的，但是有一个返回固定的委托的函数将是毫无意义的。

委托是对函数的引用，用于调用在调用站点不知道要调用的方法的函数。现在更常用的是lambda函数。下面是一个完整的应用程序，它展示了委托和lambdas (一种特定类型的委托)是如何被普遍使用的。您的例子缺少用法，因此我们无法真正帮助您。希望这有助于澄清这一概念。(请原谅布局，使用iPad)。

imports System

Public Module Module1
  Public Sub Main()

    console.Write("Enter a number:")
    Dim x as integer = if(integer.tryparse(console.ReadLine().trim, x), x, x)
    console.Write("Enter another number:")
    dim y as integer = if(integer.tryparse(console.ReadLine().trim, y), y, y)

    console.Write("Enter a plus or minus sign:")

    dim operation = console.ReadLine().Trim()

    dim op as func(Of integer, integer, integer)

    select case operation
        case "+"
            op = addressof add
        case "-"
            op = addressof minus
    end Select
    Dim result = op(x, y)


    console.WriteLine($"Result of {x} {operation} {y} is {result}")

    dim lambda as func(of integer)

    select case operation
        case "+"
            lambda = function() x + y
        case "-"
            lambda = function() x - y
    end select 

    result =lambda()
    console.writeline($"Result of {x} {operation} {y} is {result}")

  End Sub
  public Function Add(x as integer, y as integer) as integer

    return x + y

  end Function

  public function Minus(x as integer, y as integer) as integer
    return x - y
  end function
End Module