[2005] Partial Class

[danasegarane]

Hi all,
I have a partial Class as given below

'File1
Partial Public Class Employee

    Public Sub getdata(ByVal sname As String, ByVal sage As Integer)
        'What has to written
    End Sub


End Class
'File2
Partial Public Class Employee
    Private m_name As String
    Private m_age As Integer

    Private Sub setdata(ByVal sname As String, ByVal sage As Integer)
        Me.m_name = sname
        Me.m_age = sage
    End Sub


End Class

And I am creating a instance for the class as

 Dim clsEmployee As New Employee
        clsEmployee.setdata("Dam", 1)

what method i have to write to get the data from class in getData method

[alex_read]

Think of this as one single class. All the Partial specifier/keyword does is allow you to spread the class' code over several files really, so think of this as "how would I retreive those values if this class was contained in 1 file":

   Public Sub getdata(ByVal sname As String, ByVal sage As Integer)
        MessageBox.Show(m_name)
        MessageBox.Show(m_age)
    End Sub

[alex_read]

I don't know where your SetData call code is from your example above, but in order to test this from a separate class (form1 here), I needed to change the SetData scope from Private to similar to Public.

You might also want to look at using the ByRef keyword to retreive your data, or defining a structure and returning this from a GetData method which is a function as opposed to a sub. One example is like this:

File 1 Code:

Partial Public Class Employee

    Private m_name As String
    Private m_age As Integer

    Public Sub setdata(ByVal sname As String, ByVal sage As Integer)
        Me.m_name = sname
        Me.m_age = sage
    End Sub

End Class

File 2 code:

Partial Public Class Employee

    Public Sub getdata(ByRef sname As String, ByRef sage As Integer)
        sname = m_name
        sage = m_age
    End Sub

End Class

Startup Form1 file code:

Public Class Form1

    Private Sub Form1_Load(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles Me.Load
        Dim clsEmployee As New Employee
        clsEmployee.setdata("Dam", 1)

        Dim theSetSNameValue As String = String.Empty
        Dim theSetSAgeValue As Integer
        clsEmployee.getdata(theSetSNameValue, theSetSAgeValue)

        MessageBox.Show(theSetSNameValue)
        MessageBox.Show(theSetSAgeValue.ToString)
        Me.Dispose()
    End Sub

End Class

[danasegarane]

Thanks for the code alex..

How can retrive the value as a object and recast it ?

[alex_read]

I'm not too sure what you mean here, but I will guess at something like this perhaps:

    Private m_age As Object

    Public Sub setdata(ByVal sname As String, ByVal sage As Object)
        ... 
        Me.m_age = sage
    End Sub

    ...

    Public Sub getdata(ByRef sname As String, ByRef sage As Object)
        sage = m_age
    End Sub

However it is always far more efficient to use a pre-defined data type as the 1st example. If you then needed to cast this, you can use any of the following after the value has been retrieved:

1. theSetSAgeValue.ToString()
2. Convert.ToString(theSetSAgeValue)
3. Ctype(theSetSAgeValue, String)
4. DirectCast(theSetSAgeValue, String)

[danasegarane]

Any other suggestions ?

[jmcilhinney]

What's the problem? You declare a couple of variables, call GetData, pass the variables in and when the method returns those variables contain the values from the object.

That said, I can't see why you'd be using a method to get that data. Why wouldn't you just declare two properties and get each value individually?

As for partial classes, why would you use them here? I've only ever found two reasons to use partial classes:

1. I was extending a TableAdapter class that was auto-generated by the IDE, so I couldn't edit the main code file for the class.

2. I needed to use late-binding so I turned Option Strict On for the project, as I always do, then create a partial class and turned Option Strict Off for that file only. I then put all code that required late-binding in that file.

It's usually said that partial classes are good for allowing more than one person to work on the same class at the same time but I'd say that that is generally a bad idea anyway.

As for how to use them, you really don't need any practice because there's really nothing to do. You just have two or more class definitions with the same name and all, or all but one, of them must include the Partial key word in the declaration. That's it. In every other way they are exactly the same as any other class. Think about it. When you create a form the controls are all declared in a partial class. Do you have to do anything special to access them in code? No, you don't. A class is a class, whether it's declared in multiple parts or not.

[alex_read]

Thanks for posting that JMC! I attended some sort of "what's new in 2005" event ages ago where MS really plugged this feature but have never found a use for it myself. It's pretty cool to hear of some real life situation usages of the partial classes after all this time!

@danasegarane: I'd second that, not sure what you really mean by "Any other suggestions ?" here. The property suggestion is the best, or rather most professional, OOP design to go for in relation to your original sample code.