VB.NET 重载 () 运算符

Question

我是 VB.NET 的新手，正在寻找一种方法来复制 DataRow 的行为，例如。
在 VB.NET 中，我可以这样写:

Dim table As New DataTable
'assume the table gets initialized
table.Rows(0)("a value") = "another value"

现在如何使用方括号访问我的类(class)成员？我以为我可以重载 () 运算符，但这似乎不是答案。

Answer 1

它不是重载运算符，这被称为 default property .

"A class, structure, or interface can designate at most one of its properties as the default property, provided that property takes at least one parameter. If code makes a reference to a class or structure without specifying a member, Visual Basic resolves that reference to the default property." - MSDN -

两者 DataRowCollection类和 DataRow类有一个名为 Item 的默认属性.

            |       |
table.Rows.Item(0).Item("a value") = "another value"

这允许您在不指定 Item 的情况下编写代码。成员:

table.Rows(0)("a value") = "another value"

下面是一个带有默认属性的自定义类的简单示例:

Public Class Foo

    Default Public Property Test(index As Integer) As String
        Get
            Return Me.items(index)
        End Get
        Set(value As String)
            Me.items(index) = value
        End Set
    End Property

    Private ReadOnly items As String() = New String(2) {"a", "b", "c"}

End Class

Dim f As New Foo()
Dim a As String = f(0)

f(0) = "A"

给定上面的示例，您可以使用 string 类的默认属性来获取指定位置的字符。

f(0) = "abc"
Dim c As Char = f(0)(1) '<- "b" | f.Test(0).Chars(1)