Passing a default property to a new class?

07-04-2012, 11:31 AM

Gruff

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Passing a default property to a new class?

Maybe I am overthinking this...

I am making a new class that requires a lot of input information.
Some of the properties need to be set to a default value, however I do not want to hard code them into the class.

What do you think would be the most efficient way to populate these properties?

I've been thinking of making a new class to hold all the default props and pass them as one object into the new class as a single argument but it seems kind of clunky.

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07-04-2012, 01:17 PM

AtmaWeapon

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That's actually one of the more convenient ways to go about it. If you do it that way, you can have several pre-configured instances of the configuration class to make it easier on yourself. Consider this approach using an imaginary BackgroundWorker class since it has 2 Boolean properties you might want to configure:

Code:

Class BackgroundWorkerConfiguration
    Public Property ReportsProgress As Boolean
    Public Property SupportsCancellation As Boolean

    Public Shared ReadOnly Property WithProgressAndCancellation As BackgroundWorkerConfiguration
        Get
            Dim value As New BackgroundWorkerConfiguration()
            value.ReportsProgress = True
            value.SupportsCancellation = True
            Return value
        End Get
    End Property
End Class

' somewhere in code:
Dim worker As New BackgroundWorker(BackgroundWorkerConfiguration.WithProgressAndCancellation)

An alternative is using a factory pattern. Make a class with methods that does the icky configuration for you:

Code:

Class BackgroundWorkerFactory

    Public Shared Function WithCancellation() As BackgroundWorker
        Dim value As New BackgroundWorker()
        value.SupportsCancellation = True
        Return value
    End Function
...

Either way, you end up having to do the icky typing work /somewhere/, but at least it's limited to one place.

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07-04-2012, 03:26 PM

Gruff

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My understanding of the backgroundworker is fuzzy at best so your example poses more questions than answers for me.

This is what I was thinking.

Code:

Public Class Form1()
  Private oCarDefaults as New VehicleDefaults(4,4,false)
  '...
  'Elsewhere in an event :  oCarDefaults = New VehicleDefaults(6,2,True)  Then create a slew based on these defaults. 

End Class

Public Class Vehicle
  Public Property Defaults = Nothing
  Public Property VehicleColor as color
  Public Property License as string = ""
  '...

  Public Sub New(defauits as vehicledefaults, vehiclecolor as color, license as string, ...)
    Defaults = defaults
    VehicleColor = vehiclecolor
    License = license
    '...
  End Sub
End Class

Public Class VehicleDefaults
  ' This class is created only once.
  ' Defaults are changed rarely if at all.

  Public Cylinders as integer = 0
  Public Seats as integer = 0
  Public Convertable as boolean = false
  '...
  Public Sub New(cylanders as integer, seats as integer, convertable as boolean)
    ' Set Props 
  End Sub
End Class

The idea is to reduce the number of parameters and the number of times you have to set them.

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