I've global variables in module level with below COM-interface types.
Imports System.IO
Imports simpackcomslvLib
Imports simpackcompostLib
Module Globals
Public Srv As SpckCOMApp
Public Mdl As IScrModel
Public Post As PostComApp
Public Res As PostComProject
End Module
In another classes some of my procedures change their object values. I'd like to run some of my procedures which made some changes on my tool's GUI when the for example Mdl value is changed.
I tried with below method which made for an integer type parameter but i didnt succeded for my case, i think because of their object(I types belongs to COM-interface.
Public Class myVar
Private mValue As Integer
Public Event VariableChanged(ByVal mvalue As Integer)
Public Property Variable() As Integer
Get
Variable = mValue
End Get
Set(ByVal value As Integer)
mValue = value
RaiseEvent VariableChanged(mValue)
End Set
End Property
End Class
Usage of above code in an example
Public Class Form1
Private WithEvents test As New myVar
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
test.Variable = CInt(TextBox1.Text)
End Sub
Private Sub VariableChanged(ByVal NewValue As Integer) Handles test.VariableChanged
MessageBox.Show(NewValue)
End Sub
End Class
Is there anyway to implement my below variables in a module such a way also using in module level is wrong should i move them under the class?
Module Globals
Public Srv As SpckCOMApp
Public Mdl As IScrModel
Public Post As PostComApp
Public Res As PostComProject
End Module
Related
Let's assume following example below:
When I call Form2 from Form1 and pass _name of Form1 value. When I show Form1's _name = Alex? I didn't change pname in Form2 and constructor doesn't contains ByRef.
Example code:
Public Form1
Public _name as String
Sub New
_name = "John"
Dim bla as New Form2(_name)
'now _name=Alex !!
End Sub
End Class
Public Form2
Property _name2 as String
Sub New(pname as String) 'no ByVal !!
_name2 = pname 'even if would be ByVal no pname changed !
_name2 = "Alex"
End Sub
End Class
Why is that happening?
Use Shared in variable _name:
Class Form1
Public Shared _name As String
Public Sub New()
_name = "John"
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' Message "John"
MessageBox.Show(_name)
Dim bla As New Form2()
bla.Show()
' Message "Alex"
MessageBox.Show(_name)
End Sub
End Class
Public Class Form2
Property _name2 As String
Sub New()
_name2 = "Alex"
Form1._name = _name2
End Sub
Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' message Alex
MessageBox.Show(_name2)
' message Alex
MessageBox.Show(Form1._name)
End Sub
End Class
Or
When the modifier is not entered in the signature of a constructor (method), the default is byVal. If you want to change the value of the variable in form2 you must inform byref in the form2 constructor signature:
Sub New (byref _name as String)
To change the underlying value of an argument you must use the ByRef modifer:
Specifies that an argument is passed in such a way that the called procedure can change the value of a variable underlying the argument in the calling code.
This differs slightly from ByVal:
Specifies that an argument is passed in such a way that the called procedure or property cannot change the value of a variable underlying the argument in the calling code.
By not specifying a modifier in VB.NET the compiler by default will use ByVal.
It would be good to note here that although VB.NET uses ByVal by default if not specified, VBA does not and instead by default uses ByRef. Beware of this should you ever port code from one to the other.
Furthermore you are changing name2 when instead you should be changing pname if you want to change the underlying value.
Have a look at the following code based on your example:
Public Class Form1
Private _name As String
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
_name = "John"
Dim bla As New Form2(_name)
bla.Show()
Debug.WriteLine(_name)
End Sub
End Class
Public Class Form2
Private Property _name2 As String
Public Sub New(ByRef pname As String)
InitializeComponent()
_name2 = pname
pname = "Alex"
End Sub
End Class
Before passing the value to Form2 the name is "John":
At this point I am changing the value of pname to "Alex":
Note that although I have changed the value of pname To "Alex", _name2 is still set to "John".
Notice how the value of _name changes to "Alex" because of the change made to pname:
I'm not sure what it is you're trying to achieve here but hopefully this example gives you a better understanding. The alternative way would be to use a shared variable as explained in the other answer.
I am using VS2008/.net fw 3.5sp1 and back into the coding life - and a little rusty to say the least :) Any help on the below would be great please.
I need to gather a list of input from a user, that I will work with later (pass to a teradata DWH with some other values). The input list involves two parts, a BSB ID and an Account ID. After some research it looks like the best option would be to create a class for the accounts, a list of accounts and bind that to a datagridview - of which I have done - but it looks like I can't add/edit. I have added a new button/add button to alter the data grid and get an error that I cannot programmatically add.
When I use accountList.AllowNew() = TRUE -- Error -- constructor on type bankaccount not found - but - I thought the constructor is the "new" sub in the class?
When I try accountsBindingSource.IsFixedSize = False it advises the property is read only.
For this - I've cut all the other code out to just this section, which requires one form (frmAccountLoad), with a datagridview dgvAccounts and a button btnNewLine.
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Data.Common
Imports System.Diagnostics
Imports System.Drawing
Imports System.Data.SqlClient
Imports System.Windows.Forms
'--------------------------------------------------------------------
Public Class frmAccountLoad
' This BindingSource binds the list to the DataGridView control.
Private accountsBindingSource As New BindingSource()
Private Sub frmAccountLoad_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'Create list to hold accounts
Dim accountList As New BindingList(Of BankAccount)
accountList.AllowNew() = True
'accountList.AllowEdit = True
accountsBindingSource.DataSource = accountList
dgvAccounts.DataSource = accountsBindingSource
'dgvAccounts.Columns(0).HeaderText = "BSB"
'dgvAccounts.Columns(1).HeaderText = "Account"
End Sub
Private Sub btnNewLine_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNewLine.Click
'accountsBindingSource.IsFixedSize = False
accountsBindingSource.AddNew()
End Sub
End Class
'--------------------------------------------------------------------
Public Class BankAccount
'----------------------------------------------------------
'a bank account has both a BSB and an account number
Private m_BSB As String
Private m_Account As String
'----------------------------------------------------------
'Public Property
Public Property BSB() As String
Get
Return m_BSB
End Get
Set(ByVal value As String)
m_BSB = value
End Set
End Property
Public Property Account() As String
Get
Return m_Account
End Get
Set(ByVal value As String)
m_Account = value
End Set
End Property
'----------------------------------------------------------
Public Sub New(ByVal new_Bsb As String, ByVal new_Account As String)
m_BSB = new_Bsb
m_Account = new_Account
End Sub
End Class
To be able to call AddNew on your BindingList the BankAccount should have a parameter-less constructor.
You need to have a public parameter-less constructor if you need some initialization, or just remove any constructor if you don't need initialization, then the default parameter-less constructor will be used.
Public Class BankAccount
Public Property BSB As String
Public Property Account As String
Public Sub New()
'Do initialization here if you need
'Or Remove the constructor if you don't need any initialization.
End Sub
End Class
Also you don't need to set accountList.AllowNew = True. It's enough to use a BindingList(Of T) as DataSource.
Private accountList As BindingList(Of BankAccount)
Private Sub frmAccountLoad_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
accountList = New BindingList(Of BankAccount)
dgvAccounts.DataSource = BS
End Sub
Then you can call accountList.AddNew() wherever you need.
I'm making my own message box class (called MessageBoxC, whatever), and like System.Windows.Forms.MessageBox, I want to make my class with no constructors and no possibility to declare a new instance of it.
E.g.:
Public Class MessageBoxC
Public Overloads Sub Show(ByVal message As String)
Me.Message = message
ProcessData() '(*)
Me.ShowDialog()
End Sub
End Class
Public Class Form1
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
System.Windows.Forms.MessageBox.Show("Hello World!") 'works fine
MessageBoxC.Show("Hello World!") 'works fine
Dim msgBox As New System.Windows.Forms.MessageBox 'and you'll get an error message here (**)
Dim msgBoxC As New MessageBoxC 'no error message
End Sub
End Class
(*) Not important. It just calculates text size (width and height in pixels) to correct form size if needed and the corresponding label gets value of Me.Message property.
(**) This one is what I mean. You cannot make a new instance of a MessageBox class, you'll get following error-message: "Type System.Windows.Forms.MessageBox has no constructors."
Well, my class has also no constructors, but it's possible to declare an instance of it. What's the trick here?
Thanks a lot!
Solved. Thanks to OneFineDay.
Public Class MessageBoxC
Private Sub New()
'Empty
End Sub
Public Overloads Shared Function Show(ByVal message As String) As System.Windows.Forms.DialogResult
Return Show(message, Constants.MyAppName, Constants.messageTitle, MessageBoxCButtons.OK, MessageBoxCIcon.Undefined)
End Function
Public Overloads Shared Function Show(ByVal message As String, _
ByVal caption As String, _
ByVal title As String, _
ByVal buttons As Library.MessageBoxCButtons, _
ByVal icon As Library.MessageBoxCIcon) As System.Windows.Forms.DialogResult
Dim msgBoxC As New CBox(message, caption, title, buttons, icon)
msgBoxC.ShowDialog()
Return msgBoxC.DialogResult
End Function
Private Class CBox
Inherits System.Windows.Forms.Form
Sub New(ByVal message As String, _
ByVal caption As String, _
ByVal title As String, _
ByVal buttons As Library.MessageBoxCButtons, _
ByVal icon As Library.MessageBoxCIcon)
MyBase.New()
InitializeComponent()
Me.Message = message
Me.Text = caption
Me.Title = title
Me.Buttons = buttons
Me.Icon64 = icon
Me.OptimizeMe()
End Sub
End Class
End Class
Public Class Form1
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
Dim dialogResult As New DialogResult
dialogResult = MessageBoxC.Show("This is a simple message.")
MessageBox.Show(dialogResult.ToString)
End Sub
End Class
If you don't declare any constructors, a default constructor is automatically created (this is a public constructor with no parameters).
To prevent anyone creating an instance of your class, you can create a private constructor, like so:
Public Class MessageBoxC
Private Sub New()
' Prevents anyone creating an instance of this class.
End Sub
End Class
Note that your Show method will need to be declared Shared, otherwise you won't be able to call it. In fact, it would need to be Shared, even with the code you provided.
Here is one way to hide the constructor - mainly because the class in question is not accessible.
Public Class Form1
Private Sub meLoad() Handles Me.Load
'Usage
FooBar.Show("Hi")
End Sub
'...
End Class
Public Class FooBar
Private Sub New()
End Sub
Public Shared Sub Show(message As String)
Dim mbc As New MessageBoxC(message)
mbc.ShowDialog()
End Sub
'MessageBoxC is not exposed outside of Foobar which is the entry point
Private Class MessageBoxC : Inherits Form
'define cTor's as needed
Public Sub New(message As String)
Me.Text = message
End Sub
'define content
End Class
End Class
What I have is an object that contains a list of objects that each contain another list of objects that have properties and such.
Currently I use pass-through methods to be able to add to those nested objects, like in this extremely simplified example:
Public Class clsA
Private objB As List(Of clsB) = New List(Of clsB)
Public Sub New()
objB.Add(New clsB)
End Sub
Public Sub AddInt(ByVal BIndex As Int32, ByVal CIndex As Int32, ByVal Number As Int32)
objB(BIndex).AddInt(CIndex, Number)
End Sub
End Class
Public Class clsB
Private objC As List(Of clsC) = New List(Of clsC)
Public Sub New()
objC.Add(New clsC)
End Sub
Public Sub AddInt(ByVal CIndex As Int32, ByVal Number As Int32)
objC(CIndex).AddInt(Number)
End Sub
End Class
Public Class clsC
Private lstNum As List(Of Int32) = New List(Of Int32)
Public Sub AddInt(ByVal Number As Int32)
lstNum.Add(Number)
End Sub
End Class
It seems like proper coding standards would tell me this is correct compared to:
Public Class clsD
Public objE As List(Of clsE) = New List(Of clsE)
Public Sub New()
objE.Add(New clsE)
End Sub
End Class
Public Class clsE
Public objF As List(Of clsF) = New List(Of clsF)
Public Sub New()
objF.Add(New clsF)
End Sub
End Class
Public Class clsF
Public lstNum As List(Of Int32) = New List(Of Int32)
End Class
Are there some instances where either method would be acceptable? Or would the pass-through setup always be preferred?
Public Class Form1
Dim oA As clsA = New clsA
Dim oD As clsD = New clsD
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
oA.AddInt(0, 0, 3)
oD.objE(0).objF(0).lstNum.Add(3)
End Sub
End Class
Think about how it's done throughout the .NET Framework. The collection should be assigned to a private field and exposed via a public read-only property.
Public Class Thing
Private _stuff As New List(Of Thing)
Public ReadOnly Property Stuff() As List(Of Thing)
Get
Return _stuff
End Get
End Property
End Class
The caller can then access the collection directly to call its Add method, etc, but cannot assign a whole new collection. There are examples everywhere: Control.Controls, ListBox.Items, ComboBox.Items, ListView.Items, DataSet.Tables, DataSet.Relations, DataTable.Rows, Datatable.Columns, etc, etc, etc.
can we have a single global variable which can be manipulated by multiple forms
In short, yes. You can have a global variable in a module (.mod) file or a class (.vb) file.
Module Module2
Public variable As String = "Testing"
End Module
Declare a variable like this:
Public Shared myVariable as Type
and access it from any form.
You can access a single variable from any form, if it is declared as public.
If you are defining it in form1 and want to use it in form2, then from inside form2 you can call the variable as - form1.<variable_name>
Take an example-
Form1 code
Public Class Form1
Public a As Integer = 10
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Form2.Show()
End Sub
End Class
Form 2 code
Public Class Form2
Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
MsgBox(Form1.a)
End Sub
End Class
Yes, it can be done. If you declare it as shared it will exist in only one instance.
Public Class SomeClass
Public Shared SomeField As String
End Class
I would, however, recommend to wrap access to the field into a property:
Public Class SomeClass
Private Shared _someValue As String
Public Shared Property SomeProperty() As String
Get
Return _someValue
End Get
Set(ByVal value As String)
_someValue = value
End Set
End Property
End Class
By wrapping it into a property you will make it easier to troubleshoot problems around the value in case such scenarios would appear in the future.
What you are looking for is the "singleton pattern".
But first, you should ask yourself if you really need it. Maybe this variable could be passe as a parameter to a function or a property.
Use
Public x As Integer
On any Of the Forms and then when you want to use that variable on other form then you can type the form name and then a dot and then the variable name
like this
form1.x
Cheers!!!