VB.NET from beginner to advanced programmer Part 19 - Enumerations

[Vswe]

Welcome to the VB.NET tutorial series: "VB.NET from beginner to advanced programmer" which will take you from the very beginning to be a good programmer. VB.NET is a good first language for new programmers so this 21 part long series is written for completely beginners but it will also works perfectly fine if you already know another programming language.


VB.NET from beginner to advanced programmer

1. Introduction and Installation
2. Objects and Events
3. Variables
4. The basic data types
5. Logical Operators
6. Relational Operators
7. If statements Then
8. Arithmetical Operators
9. Loops Part 1
10. Arrays
11. Loops Part 2
12. Try Catch statements
13. Subs and Functions
14. Difference between Scopes
15. Select Statements
16. Multidimensional arrays
17. Structures
18. Classes
19. Enumerations
20. Advanced Comments
21. Compiling Directives

In this part it's time for something called Enums which is short for Enumerations. Enums is used when you have some unchanging values which is related to each other in some way or another. So then you "group" them together and give them a name.

You create an Enum like this:

Private Enum MyEnum
    Member1
    Member2
    Member3
End Enum

So here we created an Enum called MyEnum with the three members: Member1 (which got the value 0), Member2 (value 1) and Member3 (Value 2).

We can also give the members specific values:

Private Enum MyEnum
    Member1 = 10
    Member2 = 15
    Member3
End Enum

Since we haven't given Member3 any value it will get the value of the member above + 1(16).




I understands if you didn't understood how, when and why to use Enumerations. I show you an example to explain it better:



Without Enums:

With an ID of an animal/object we uses a function to get the number of legs it have. We have to remember all IDs to get it right.

    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        MessageBox.Show(Legs(1))
    End Sub


    Private Function Legs(ByVal animal As Integer)

        Select Case animal
            Case 0 'Snake
                Return 0
            Case 1 'Dog
                Return 4
            Case 2 'Human
                Return 2
            Case 3 'Three legged table
                Return 3
            Case 4 'Cat
                Return 4

        End Select

    End Function

With Enums


Now instead we'll create an Enum called Animals, we've changed the parameter to be of the type Animals, and changed the Select Case statements' values too:

    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        MessageBox.Show(Legs(Animals.Dog))
    End Sub


    Private Function Legs(ByVal animal As Animals)

        Select Case animal
            Case Animals.Snake
                Return 0
            Case Animals.Dog
                Return 4
            Case Animals.Human
                Return 2
            Case Animals.Table
                Return 3
            Case Animals.Cat
                Return 4

        End Select

    End Function



        Private Enum Animals
        Snake
        Dog
        Human
        Table
        Cat
    End Enum

That was the version which looked liked the one without Enums but were a lot easier to read and use. But we can completely remove the Select Case statement and the function, like so:

    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        MessageBox.Show(Animals.Dog)
    End Sub


    Private Enum Animals
        Snake = 0
        Dog = 4
        Human = 2
        Table = 3
        Cat = 4
    End Enum

In the code above I gave all members in the Enum the value we wanted. Then I just show "Animals.Dog" in a messagebox. The output was 4.




A very good thing with Enums is that you'll have a list of all the values as you can see in the example below. That example is showing all members of the Enum DialogResult which is used to see which button that was pressed on a messagebox. So now you also got an example on an inbuilt Enum.






That was pretty much it. Hope you understood how, when and why to use Enumerations. In the next part I'll teach you about some more advanced commenting. Till then.

[Jordan]

Very cool and useful! +rep