Testing to see if enumeration variable has been populated

  • Thread starter Thread starter mrchillisauce
  • Start date Start date
M

mrchillisauce

I have an class that has a member that is an enumeration.

When the property that exposes this is accessed I want to check if it has a
value and if not assign it a default one.

private _EnumX as EnumX

public readonly property XXXX as EnumX
Get
If _EnumX is Nothing then
_EnumX= EnumX.AnItemInTheEnum
End If
Return _EnumX
End Get

As Enums are value type this cannot be done...

What is the best way to do this?

Thanks
 
The wasy I see of acheiving this is by setting the defaukt in the private
variable declaration. I was just wondering if the is a statement analagous to
the If enumX is nothing,
 
The wasy I see of acheiving this is by setting the defaukt in the private
variable declaration. I was just wondering if the is a statement analagousto
the If enumX is nothing,











- Show quoted text -
Click to expand...

Yes, the best way is to:

private _EnumX as EnumX = EnumX.AnItemInTheEnum

Public Readonly Property XXX as EnumX
Get
return _EnumX
End Get
End Property

When the class is instantiated, it will set the value of _EnumX to
EnumX.AnItemInTheEnum - hence it has a default value at creation time.
 
As an enum is a value type, it has a default value of 0. You cannot do an
Is Nothing test becuase the Is operator is for references only. You can
however do an = Nothing test, e.g If _EnumX = Nothing Then ...

If this class is exposed to a designer, such as a control or componenet,
then you want to set the default value attribute as well, eg:

Private m_XXXX As EnumX = EnumX.AnItemInTheEnum

<System.ComponentModel.DefaultValue(GetType(AcceptRejectRule),
"EnumX.AnItemInTheEnum")> _
Public Property XXXX() As EnumX
Get
Return m_XXXX
End Get
Set(ByVal value As EnumX)
m_XXXX = value
End Set
End Property
 
Hi Bill,

Why sometime does the obvious not occur to me :-)
I dont know why I didnt just think of = Nothing instead of Is Nothing

What does the AcceptRejectRule in the defaultvalue do? Intellisense is
telling me its to do with DataSets or DataTables...

Thanks
 
mrchillisauce said:
Hi Bill,

Why sometime does the obvious not occur to me :-)
I dont know why I didnt just think of = Nothing instead of Is Nothing

What does the AcceptRejectRule in the defaultvalue do? Intellisense is
telling me its to do with DataSets or DataTables...
Click to expand...


Sorry, my bad. It was a cut and paste error using an existing enum ;)
Should have read as:

Private m_XXXX As EnumX = EnumX.AnItemInTheEnum

<System.ComponentModel.DefaultValue(GetType(EnumX),
"EnumX.AnItemInTheEnum")> _
Public Property XXXX() As EnumX
Get
Return m_XXXX
End Get
Set(ByVal value As EnumX)
m_XXXX = value
End Set
End Property
 
mrchillisauce said:
Why sometime does the obvious not occur to me :-)
I dont know why I didnt just think of = Nothing instead of Is Nothing
Click to expand...

Just note that 'Nothing' does not mean "no value" for value types. It
simply means "default value", which is the value 0 for enums. However, this
value can be a named enum constant!
 
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