CODEWITHSUNDEEP
vb.netfunctionevents
user2733082
user2733082

Reputation:

VB.net Class event that raises when a shared function is called from another class/object?

How can I create or use an event that raises when you call a shared sub/function from another object or class?

I'll show an example: I have the class DataHost that access a database:

Class DataHost

Shared Sub addName().....
Shared Sub delName().....
Shared Function getNames()....

Shared Function askPassword()........

End Class

I want the program to ask for the password every time another class calls the subs/functions of DataHost to access the database.

I could add at the beginning of each function if askpass()=False Then return but in my code the functions are more than 20 and I would like to have a more intelligent solution.

So I am looking for something that calls askPassword() whenever you call another sub/function.

Upvotes: 3

Views: 4941

Answers (2)

WozzeC
WozzeC

Reputation: 2660

Alright this might not at all be what you are requesting, but I'll post the code for a shared event then you can see if you can use it in any way. (This is my log event so do overlook the naming)

Public Class Logging
    Public Shared Event LogEvent As EventHandler
    Public Shared Sub OnLogWrite(ByVal Sender As Object)
        RaiseEvent LogEvent(Sender, New EventArgs)
    End Sub
End Class

This is the shared event that you will have to listen to. You can add a handler to LogEvent wherever you want. And it will fetch all calls to this. Here you would be able to create a Shared Variable that keeps track of the Sender value. For example a List(of Object).

You raise the event anywhere (except from within a Shared method or function, since there is no instance) with:

Logging.OnLogWrite(Me)

And you can listen to the event anywhere with:

AddHandler Logging.LogEvent, AddressOf HandleLogEvent

The code for HandleLogEvent looks like this:

Private Sub HandleLogEvent()
    MessageBox.Show("Hello.")
End Sub

HandleLogEvent could for example be renamed to askPassword. Which means that if no check is made in the OnLogWrite Sub. Then Anytime the event is called, askPassword would be executed. Hope this helps you in some way.

Upvotes: 6

Rex
Rex

Reputation: 2140

i would suggest not to use shared methods for all the functions and allow them be called only through instances. Then limit the instantiation (constructor) process. a quick sample: 

Class DataHost
    Shared Function GetHost() As DataHost
        If askPassword() Then
            Return New DataHost()
        End If

        ' Or do something else instead of throw nothing
        Return Nothing
    End Function

    Shared Function askPassword() As Boolean
        ' ask for password?
    End Function

    ''' <summary>
    ''' Private constructor to avoid external instantiation - thus force external calls to go through factory: GetHost()
    ''' </summary>
    ''' <remarks></remarks>
    Private Sub New()
    End Sub

    Sub addName()

    End Sub


    Sub delName()

    End Sub

    Function getNames() As IEnumerable(Of String)

    End Function

End Class

here you can see to call GetNames(), the caller has to have an instance of the DataHost, however, due to the private constructor, the caller has to get an instance of the DataHost through factory method GetHost().

and if you don't want to have many copies of DataHost, you could use singleton as well and return it out in the GetHost() method when password is provided.

EDIT: if you really want an event raised out during the process, you could do so at the GetHost method as well: create a private method in the DataHost to raise an event, then after the DataHost is instantiated, call it to throw out the event:

    Shared Function GetHost() As DataHost
        If askPassword() Then
            dim host = New DataHost()
            host.RaiseSomeEvent() 
        End If

        ' Or do something else instead of throw nothing
        Return Nothing
    End Function

then externally the event could be subscribed and handled.

  • Tweak it according your needs.

Upvotes: 0

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