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Property help

Posted on 2006-07-11
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Last Modified: 2010-04-23
Don't ask me why - but I still struggle with GETs and SETs.
Anyone care to walk me through this - preferrably using semi-real-world scenarios?
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Question by:sirbounty
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Expert Comment

by:Fernando Soto
ID: 17083633
What question do you have properties, Set and Get?
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Author Comment

by:sirbounty
ID: 17083650
I get them confused.  I can't seem to get it straight which does what...
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Assisted Solution

by:Carl Tawn
Carl Tawn earned 200 total points
ID: 17083652
Set is used to assign a value to a property, Get is used to retrieve it:


    Public Property FirstName As String
        Get
            Return _firstName
        End Get
        Set
            _firstName = value             '// value is a keyword implicitly defined for properties
        End Set
    End Property
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LVL 67

Author Comment

by:sirbounty
ID: 17083658
Let's say I have a textbox control.
If I want to pass the user entered value to that textbox UserText property - would that be a set?
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Expert Comment

by:Carl Tawn
ID: 17083663
Yes.
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Author Comment

by:sirbounty
ID: 17083670
And I always "get" my property's value from the "set"?

So, if I've "set" UserText to be "John Doe" and I later want to retrieve the value, it runs through the "Get" which says
Return mstrUserName

but that process of 'returning' the value gets it from where?  Simply from the module-declared mstrUserName?

Am I kind of close?
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Assisted Solution

by:Carl Tawn
Carl Tawn earned 200 total points
ID: 17083705
Yup.

    Public Class Person

        Private _firstName As String

        Public Property FirstName As String
            Get
                Return _firstName
            End Get
            Set
                _firstName = value             '// value is a keyword implicitly defined for properties
            End Set
        End Property

    End Class
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Accepted Solution

by:
Shakti109 earned 200 total points
ID: 17083713

Public Class MyNewClass
    Private MyString as string

    Public Property TheString As string
        Get
            Return MyString
        End Get
        Set(ByVal Value As String)
            MyString = Value
        End Set
    End Property
end class

Ok, basically this has set up :

You have an object that is "internal" to this class : "MyString".
 You have an object that is "externally readable and set-able"  : "TheString"
   This object "TheString" is a reference to "MyString". It allows you to set the internal object with a publicly accessible   method.

In the "GET" portion of the class, you are simply returning the internal object "MyString" through the access property "TheString".

As an example of "getting" this item out of the class you would use :

Dim NewClass as MyNewClass
Textbox1.Text = NewClass.TheString

In the "SET" portion of the class, you are actually setting the internal object "MyString" by using the publicly accessible item "TheString", example :

Dim NewClass as MyNewClass
NewClass.TheString = "SomeValue"

When you go back and "Get" this, you will get that new value : "SomeValue".

Basically, you are turning the class into a "black box", for which the internal properties can only be modifed or viewed by the functions (get / set) you provide.

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Author Comment

by:sirbounty
ID: 17083738
I just hope it sticks.
Thanx for taking the time to explain it. :^)
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Expert Comment

by:Carl Tawn
ID: 17083755
You can also drop either the Set or Get to create read/write only properties. But if you do you need to explicitly tag them as such:

    Public WriteOnly Property Something() As String
        Set(ByVal Value As String)
            _something = Value
        End Set
    End Property

    Public ReadOnly Property SomethingElse() As String
        Get
            _somethingElse
        End Get
    End Property


Forgot the (ByVal value As String) bit in my last posts....to used to C# :o)
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