Array of Structs

[mk48]

I am trying to create and initialize an array of structs of a fixed size. Each struct will be populated when a button is clicked. Here is an example of my struct:

public structure buttonStruct

dim x() as Boolean
dim y() as Boolean
dim z as Boolean
dim q as integer

Public Sub Initialize()

Me.x = New Boolean(32) {}
Me.y = New Boolean(32) {}
Me.z = New Boolean
Me.q = New integer
End Sub

end structure

In my form_load function I am declaring the array of structs and:

Dim BtnStruct(15) As ButtonStruct
BtnStruct(0).Initialize()
BtnStruct(1).Initialize()
.
.
BtnStruct(15).Initialize()

Whenever a specific button is clicked, I am trying to collect data and store it in the respective struct and so for example, if button 1 is clicked then I will store the data associated with button 1 into BtnStruct(0). The position of the button is stored in a public variable called BtnNum. If I attempt to store information in the struct inside another function as follows, I receive an error

BtnStruct(BtnNum).x(pos - 1) = temp

"btnstruct is not declared. it may not be inaccessible due to its protection level"

Any ideas?

[Niya]

Dim BtnStruct(15) As ButtonStruct

The above should be at the form level, you declared it in Form_Load

[mk48]

Thanks for the response. I knew it was something silly. Do you have any recommendations regarding how to initialize all of the elements within the struct array? Is my approach okay as far as using an Initialize function:

BtnStruct(0).Initialize()
BtnStruct(1).Initialize()

Is it better to initialize each struct element when the data is going to be stored in the struct instead of initializing all of the struct elements in the form_load?

[Niya]

Thats about the only way you can initialize a structure, however if you declared it as a class instead you could do this:-

Public Class buttonStruct
 
        Dim x() As Boolean
        Dim y() As Boolean
        Dim z As Boolean
        Dim q As Integer
 
        Public Sub New()
 
            Me.x = New Boolean(32) {}
            Me.y = New Boolean(32) {}
            Me.z = New Boolean
            Me.q = New Integer
        End Sub
 
    End Class

Note that classes are reference types and structures are value types so if you decide to change it, be aware of this important difference.

[Shaggy Hiker]

I was going to write that your code won't work because of this line:

BtnStruct(BtnNum).x(pos - 1) = temp

but it actually should, though only because x is a reference type (an array). If you try something like that with z or q, then it will fail, because when this part runs:

BtnStruct(BtnNum)

it will return a copy of the structure, and the rest of the line makes changes to the copy and not to the instance that is in the array. However, since you are making changes to a reference type in the copy, then it will work because the copy holds a copy of the reference, not a copy of the array. Otherwise, if you use structures in that way, what you have to do is this:

Dim tempButtonStruct = BtnStruct(BtnNum)

'make your changes on tempButtonStruct

BtnStruct(BtnNum) = tempButtonStruct

In other words, make a copy, change the copy, then save the copy back into the array, thereby replacing the structure that is in there.

[jmcilhinney]

when this part runs:

BtnStruct(BtnNum)

it will return a copy of the structure.

I used to think that too but, as it turns out, arrays are a little different to what you might expect in that indexing gives you the actual value, not a copy. Try this code to see that in action:

Public Class Form1

    Private Structure X
        Public Y As Integer
    End Structure

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim a(0) As X

        'This will create a copy.
        Dim b = a(0)

        'This won't.
        a(0).Y = 100

        MessageBox.Show(a(0).Y.ToString())
        MessageBox.Show(b.Y.ToString())
    End Sub

End Class

[techgnome]

Where you get into the problem with copy vs actual structure is with iterators ... for each and the like.... stepping through an array with index though should be safe.

-tg