vb.net Get and Set question

Question

0.00/5 (No votes)

See more:

I am new to OOP and vb.net, up till now i have been coding in VBA. I am really having a hard time understanding the difference between the Class Get/Set vs. just using a public function with a private variable. What is porpoise of Get/Set. The code below is what i do when i need to get a private variable.

VB

Public Class Dog
    Private DogRunning as Boolean


    Public Function IsDogRunning()
       'Find Out if Dog is Running
       If DogIsRunning then 
            DogRunning = True
       Else
            DogRunning = False
       End If

       Return DogRunning
    End Function
End Class

Thank you in advance,

-J

Posted 18-May-12 14:02pm

juno101

Add a Solution

4 solutions

Solution 4

Adding to what has already been said, a Property DOES create two Functions 'under the hood'.
When looking at the generated IL (Intermediate Language[^], this is the language that both VB and C# are translated into when compiled and that actually runs your application) you'll see that a Property such as the following:

VB

' Sample code from VJ Reddy's answer.
Private mBodyColor As Color
Public Property BodyColor() As Color
    Get
        'Do some work
        Return mBodyColor
    End Get
    Set(ByVal Value As Color)
        mBodyColor = Value
        'Do some validation and any other relevant work
    End Set
End Property

Generates two functions in IL, get_BodyColor and set_BodyColor.
So basically a Property is a call to a get and set function.
Why you should use a Property in .NET instead of a Public field has already been said I think. For me the most important reason is Encapsulation[^]. If, for some reason, you would have to validate values or set some other values when a field changes this can only be done through Properties or Functions. However, had you not chosen to have a Property or Function and only have a Public field then this is not possible anymore (or it would require a 'breaking change'). So why Properties instead of Functions? Properties force the programmer into an accepted and recognizable coding style where Functions do not.

Posted 19-May-12 7:37am

Sander Rossel

v2

Comments

VJ Reddy 20-May-12 0:27am

Good addition. 5!

Sander Rossel 20-May-12 5:15am

Thank you :)

Solution 2

quote

VB

Public Class Car1
    Private mBodyColor As Color
    Public Property BodyColor() As Color
        Get
            'Do some work
            Return mBodyColor
        End Get
        Set(ByVal Value As Color)
            mBodyColor = Value
            'Do some validation and any other relevant work
        End Set
    End Property
End Class

Posted 18-May-12 20:07pm

miwuawen

Updated 18-May-12 20:09pm

v2

Comments

Sander Rossel 19-May-12 13:25pm

How is simply copying the above answer a valid answer?

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

VJ Reddy · Accepted Answer · 2012-05-18T15:03:00

I have read somewhere that before introducing properties (Get/Set) in .NET, the architects of .NET have thought whether it is necessary to introduce properties, as the similar function can be obtained from the methods. Finally the properties have been introduced in .NET.
As I understand the purpose of Get/Set (Property) is as follows:

A property describes an attribute of an object. Say Color of a Car, whether the car has AC like so.

The Setter and Getter blocks are cohesively encapsulated into a single member of the object i.e. the Property
For eg.

VB

Public Class Car1
    Private mBodyColor As Color
    Public Property BodyColor() As Color
        Get
            'Do some work
            Return mBodyColor
        End Get
        Set(ByVal Value As Color)
            mBodyColor = Value
            'Do some validation and any other relevant work
        End Set
    End Property
End Class
Public Class Car4
    Private mBodyColor As Color
    Public Function GetBodyColor() As Color
        'Do some work
        Return mBodyColor
    End Function
    Private Sub SetBodyColor(ByVal value As Color)
        mBodyColor = value
        'Do some work
    End Sub
End Class

In the above example in Car1 class the property is used which has both Get and Set methods.
Using methods for the same purpose we have to manually name the methods like Get... and Set... so that we can recognize them together as used in Car4 class. So, there is a chance of missing if the name is not given in the above format.

With properties it is easy to designate a Property as ReadOnly or WriteOnly as below:

VB

Public Class Car2
    Private mBodyColor As Color
    Public ReadOnly Property BodyColor() As Color
        Get
            Return mBodyColor
        End Get
    End Property
End Class
Public Class Car3
    Private mBodyColor As Color
    Public WriteOnly Property BodyColor() As Color
        Set(ByVal Value As Color)
            mBodyColor = Value
        End Set
    End Property
End Class

Same thing can be accomplished using the methods but it is not intuitive.

Where an action is to be performed like Drive car, ChangeGear etc. then a method is used and where an attribute like Color of the car, has AC etc. are required a property is used
Validation and other actions can be performed in the Get and Set blocks of a property before returning a value and setting a value.
In some cases the dividing line between using a Property and a Method is fine and is based on experience.

I think you may get more detailed explanation from the documentation and other references. I tried to put here what I understand

[Edit]

For the case given in the question, IsDogRunning only queries the state of the Object I think the Property as below is suitable

VB

Public Class Dog
    Private mIsDogRunning as Boolean
    Public Property IsDogRunning() as Boolean
       Get
           Return mIsDogRunning
       End Get
       Set (ByVal Value as Boolean)
           mIsDogRunning = Value
       End Set
    End Property
End Class

Sangramsingh Pawar · Accepted Answer · 2012-05-19T00:11:00

Properties, internally, are nothing but a pair of methods. They basically evaluate to a get and set accessor method.

You should use properties, unless the property is going to cause some unexpected, potentially long running side effect, or there is some other good reason to use a method.

For details, I suggest reading the Property Usage Guidelines on MSDN . In particular, use a method when:

The operation is a conversion, such as Object.ToString.
The operation is expensive enough that you want to communicate to the user that they should consider caching the result.
Obtaining a property value using the get accessor would have an observable side effect.
Calling the member twice in succession produces different results.
The order of execution is important. Note that a type's properties should be able to be set and retrieved in any order.
The member is static but returns a value that can be changed.
The member returns an array.
Otherwise, I'd use a property. Brad Abram's blogged some other details, including good reasons why certain API functions use methods (mostly because they could cause cross-computer communication, which would fall into the "side effect" category).