Convert String to custom Class Type in Vb.net

问题

Most of the search results I've found have turned up to be the opposite of what I'm looking for so here's my question:

I'm trying to convert System types into custom types of my own but as I mentioned, my search results have not been effective and give me the opposite of what i'm looking for.

Say I have a String of "mystringgoeshere" and a class like:

Class MyStringType

    Dim str As String

End Class
Dim s As MyStringType = "mystringgoeshere"

And i get this error {Value of type 'String' cannot be converted to 'Project1.MyStringType'.}

I don't have any code yet really because I have no idea how to achieve this, but essentially what I want to do is set the "s" object's "str" string using a method like what i have in the code block above. I've tried using a "new(data as String)" subroutine, but it doesn't work with what i am trying.

Any ideas? thx~

回答1:

Looking at this VBCity Article on creating Custom Types It is using the Widening Operator.

from last link:

Widening conversions always succeed at run time and never incur data loss. Examples are Single to Double, Char to String, and a derived type to its base type.

so try something like this

Public Class Form1

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        Dim s As MyStringType = "mystringgoeshere"
        Dim s1 As MyStringType = "Hello"
        Dim s2 As MyStringType = s1 + s
    End Sub
End Class

Class MyStringType
    Private _string As String
    Private Sub New(ByVal value As String)
        Me._string = value
    End Sub
    Public Shared Widening Operator CType(ByVal value As String) As MyStringType
        Return New MyStringType(value)
    End Operator
    Public Overrides Function ToString() As String
        Return _string
    End Function
    Public Shared Operator +(ByVal s1 As MyStringType, s2 As MyStringType) As MyStringType
        Dim temp As String = s1._string + s2._string
        Return New MyStringType(temp)
    End Operator
End Class

回答2:

just change ur code little bit like this :

Class MyStringType 
    Dim str As String 
    Sub New(ByVal str1 As String) 
         str = str 
    End Sub 
End Class

Dim s As New MyStringType("abhi")

回答3:

what you should do is

Class MyStringType

    Dim str As String

End Class
Dim s As MyStringType 
s.str = "mystringgoeshere"

回答4:

It sounds like you want to subclass System.String. This is a fundamental of OOP programming. Inheritance is PRETTY important.

http://en.m.wikipedia.org/wiki/Inheritance_(object-oriented_programming)

来源：https://stackoverflow.com/questions/13263524/convert-string-to-custom-class-type-in-vb-net

标签

vb.net

inheritance

subclassing