How to create a Property.subProperty?

[Smithy963]

Hi Guys,

My final goal is to have a property contain 2 values, the first value will be used the normal way you would in a property,
Eg.

myClass.myProperty = "myName"

dim str as String = myClass.myProperty

and the second value, will be metaData,
Eg.

myClass.myProperty.metaData = "mySurname"

dim str as string = myClass.myProperty.metaData

-----------------------------------------------------------

Here is where I'm up to + my problem...

Public Class clsMetaData
    Private m_metaData As String
    Public Property metaData() As String
        Get
            Return m_metaData
        End Get
        Set(ByVal value As String)
            m_metaData = value
        End Set
    End Property
End Class

Public Class myTester
    Private m_myProperty As New clsMetaData
    Public Property myProperty() As clsMetaData
        Get
            Return m_myProperty
        End Get
        Set(ByVal value As clsMetaData)
            m_myProperty = value
        End Set
    End Property
End Class

Public Class settings1
    Dim myClass1 As myTester
    Public Sub DoThis()
        myClass1.myProperty.metaData = "mySurname"
        myClass1.myProperty = "myName"
    End Sub
End Class

When I use [myClass1.myProperty.metaData = "mySurname"] - Hurray, it seems I have my meta data, until I try [myClass1.myProperty = "myName"] it wont allow me to do this because I am not initializing the property with a string variable.

I cannot seem to overload this property right either because if I add in the next code section, only the return types differ, thus errors.

    Private m_myPropertyValue As String
    Public Property myProperty() As String
        Get
            Return m_myPropertyValue
        End Get
        Set(ByVal value As String)
            m_myPropertyValue = value
        End Set
    End Property

Thanks in advance for any advice and ideas,

Smithy.

[Shaggy Hiker]

I would say that a better solution would be to make two members in the metadata class, one with the name, the other with the metadata. After all, for this to work in any way, it would need to have both of those members, so why not put them into the same class?

[Smithy963]

The trouble I have then is the property grid control wont be able to automate the way it accesses my list of properties.

I need to be able to do:

myClass.myProperty1
myClass.myProperty2

it is the myClass.myProperty.metaData I am flexible with to change.

[jmcilhinney]

First up, there's really no such thing as a subproperty. The fact that you're thinking as though there is probably making it harder to achieve your aim. If I do this:

var1 = myObject.MyProperty.MySubproperty

then MySubproperty has no direct relationship to myObject or its type at all. myObject has a property named MyProperty and that property returns an object. That object has a property of its own named MySubproperty. MySubproperty is NOT a member of myObject. That code above is equivalent to this:

var2 = myObject.MyProperty
var1 = var2.MySubproperty

Also, you cannot overload a property that doesn't have any parameters. What defines the difference between overloads is the number, type and order of its parameters. If a property has no parameters then it can't be overloaded. The only properties that generally get overloaded are those that index a collection, e.g. the DataColumnCollection.Item property is overloaded because you can specify a numeric index or a name string.

[Smithy963]

I already understand why its not working,

Thank you for your help, but is there no work around to achieve this some other way.

currently I have created a metaData class, and the meta data is accessible like so...

myClass.myProperty = "string"
myClass.MetaData.myproperty = "metaString"

This isnt really ideal as I'm now using 2 separate objects instead of an object in an object...

[Shaggy Hiker]

I don't believe there is any way to achieve what you want, as what I understand your needs to be is that you want myClass.myProperty to get/set a string, while myClass.myProperty.Metadata would require myProperty to get/set a metadata object. Since that would mean that myProperty would return different things in different cases, you have some pretty bad name collision.

Aside from the option you just showed, the closest I can come to would be to move the string down into the metadata class such that myClass.MyProperty would always return a metadata object and the two versions would be:

myClass.myProperty.myString
-and-
myClass.myProperty.MetaData

[Smithy963]

As I said before, I need to be able to access string properties directly so they are automated into my PropertyGrid control.

Perhaps I will understand what I really want and how to do it someday...

but for today I will have to deal with:
myClass.myProperty
-and-
myClass.metaData.myProperty (to retrieve my properties attached metadata)

Thanks a lot for your advice,

Muchos gracias,

Smithy.

[Pradeep1210]

You would usually do:
MyClass.MySubClass.MySubClassProperty

So instead of a property what you need is a sub-class and instead of sub-property you need a property in the sub-class.

[Pradeep1210]

Do something like this for what you are trying to achieve:

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim MyClassX As New Class2
        MyClassX.MyProperty.MySubProperty = "hello"
        MsgBox(MyClassX.MyProperty.MySubProperty)
 
    End Sub
End Class
 
Public Class Class2
    Private _MyProperty As New SubClass2
    Public Property MyProperty() As SubClass2
        Get
            Return _MyProperty
        End Get
        Set(ByVal value As SubClass2)
            _MyProperty = value
        End Set
    End Property
 
    Public Class SubClass2
        Private _MySubProperty As String
        Public Property MySubProperty() As String
            Get
                Return _MySubProperty
            End Get
            Set(ByVal value As String)
                _MySubProperty = value
            End Set
        End Property
    End Class
End Class

Pradeep

[Smithy963]

Theres always somebody to jump in and raise spirits when that last shred of hope dwindles....

I take my hat off to you, It's a little more work than I envisioned since I have around 100-200 properties, but this is so stupidly obvious I cannot believe I missed it.

/bow

Thank you.

Smithy

[VBDT]

I don't think what you have showed us is posible to do. Even the above example can not give you this (what you wanted in the first place).

myClass1.myProperty.metaData = "mySurname"
myClass1.myProperty = "myName"

In the Pradeep's example myProperty is a type of subClass and it is not a string type. Is this what you wanted? but your example above is not showing that.
If we go with the logic of your example, it tells us that the string data type has a property called metadata which is not true. Isn’t myProperty a string type that takes “myName”?

[Pradeep1210]

I don't think what you have showed us is posible to do. Even the above example can not give you this (what you wanted in the first place).

myClass1.myProperty.metaData = "mySurname"
myClass1.myProperty = "myName"

In the Pradeep's example myProperty is a type of subClass and it is not a string type. Is this what you wanted? but your example above is not showing that.
If we go with the logic of your example, it tells us that the string data type has a property called metadata which is not true. Isn’t myProperty a string type that takes “myName”?

Public Property myProperty() As clsMetaData

Isn't myProperty declared as a class?

[VBDT]

Public Property myProperty() As clsMetaData

Isn't myProperty declared as a class?

Pradeep, yes it is but from his example the “MyProperty” takes a string “myName” which means it spouse to be a string type. here there is a logic error. So if we let myProperty be of a type clsMetaData than how it is possible to assign to it “myName”?
Initially as I understand he wanted to overload the property and that is not possible with properties as Jmc told it already.

[Smithy963]

I hereby decree VBDT the bringer of bad news...

aw, VBDT your point inspired me to try out a few variations of Pradeep's solution hence my opening line

Do you think I could just overload the property and give it parameter:

    Public Property ServerName() As String
        Get
            Return m_HostName
        End Get
        Set(ByVal value As String)
            m_HostName = value

        End Set
    End Property

    Public Property ServerName(ByVal metaData As Boolean) As String
        Get
            Return m_HostName_metaData
        End Get
        Set(ByVal value As String)
            m_HostName_metaData = value
        End Set
    End Property

I could then give a special attribute to the Property to hide it from the PropertyGrid control...

Thanks for bouncing some great ideas off me guys.

Smithy

[VBDT]

yes, if your properties differe by the parameter they take. the first property would not conflict with the second one because the second one has a parameter and the first one doesn't. If this is good for you than it can work. Just make a use of the parmeter, let say metaData has a property and you get or set the value of that property through the second property.

[Pradeep1210]

Pradeep, yes it is but from his example the “MyProperty” takes a string “myName” which means it spouse to be a string type. here there is a logic error. So if we let myProperty be of a type clsMetaData than how it is possible to assign to it “myName”?
Initially as I understand he wanted to overload the property and that is not possible with properties as Jmc told it already.

Ohhh.. I see now.

myClass1.myProperty.metaData = "mySurname"
myClass1.myProperty = "myName"

This was something possible in VB6 using parameterless default properties. But in .NET, default properties can't be parameterless. You must provide atleast one parameter.

So the nearest you would come to is:

'Add this property to clsMetaData
Default Public Property Prop1(ByVal n As Integer) As String
    Get
        'get value 
    End Get
    Set(ByVal value As String)
        'set value
    End Set
End Property
 
'So then you can access it like this:
myClass1.myProperty.metaData = "mySurname"
myClass1.myProperty(0) = "myName"

The other and better way is to add a function which accepts your string and returns a clsMetaData object:

Public Class clsMetaData
    Private m_metaData As String
    Public Property metaData() As String
        Get
            Return m_metaData
        End Get
        Set(ByVal value As String)
            m_metaData = value
        End Set
    End Property
 
    Public Shared Function Parse(ByVal s As String) As clsMetaData
 
        'resolve your string to object of type clsMetaData class here
 
        Dim obj As New clsMetaData
        Return obj
    End Function
 
End Class
 
Public Class myTester
    Private m_myProperty As New clsMetaData
    Public Property myProperty() As clsMetaData
        Get
            Return m_myProperty
        End Get
        Set(ByVal value As clsMetaData)
            m_myProperty = value
        End Set
    End Property
End Class
 
Public Class settings1
    Dim myClass1 As myTester
    Public Sub DoThis()
        myClass1.myProperty.metaData = "mySurname"
        myClass1.myProperty = clsMetaData.Parse("myName")
    End Sub
End Class

Pradeep

[Shaggy Hiker]

That's true, as long as you are willing to have one version take a parameter and the other take no parameter, then you can overload as much as you like. It makes the code a bit obscure, though, because the parameter is meaningless.