Please have a look at the code below:
Public Delegate Sub TestButtonClick(ByVal test As Integer)
Public Class Person
Private Name As String
Private ID As Integer
Public Event ButtonClick As TestButtonClick
Public Sub DelegateTest1(ByVal Test As Integer)
MsgBox(Test)
End Sub
Public Sub ChangeName()
RaiseEvent ButtonClick(1)
End Sub
Public Sub DelegateTest2()
MsgBox("Delegate Test 2")
End Sub
Public Sub DelegateTest3()
MsgBox("Delegate Test 3")
End Sub
End Class
Public Class Form1
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim p1 As Person = New Person
AddHandler p1.ButtonClick, AddressOf p1.DelegateTest1
AddHandler p1.ButtonClick, AddressOf p1.DelegateTest2
AddHandler p1.ButtonClick, AddressOf p1.DelegateTest3
p1.ChangeName()
End Sub
End Class
The output is:
1
DelegateTest2
DelegateTest3
I do not understand why this application compiles i.e. the delegate accepts an integer in its signature but Person.DelegateTest2 and Person.DelegateTest3 do not.
If I change Person.DelegateTest2() to the following then I do get an error as I would expect:
Public Sub DelegateTest2(ByVal Test As Integer, ByVal Test2 As Integer)
MsgBox("Delegate Test 2")
End Sub
Why does the Delegate allow you to pass zero arguments when it has arguments i.e. an integer in my case?
Don't forget that VB.NET inherits all the legacy baggage from the beloved VB. You could make it strict by putting the following to the top of your file so that it behaves as a real .NET programming language and not some hybrid crap:
Option Strict On
Also I would recommend you setting this to be the default option so that you don't find yourself in the wilderness.
Related
I want some values in a class to decrease whenever the timer in the main form ticks. I am creating multiple instances of the same class as my program is a simulation application and I am not storing these instances in an array or any list in that matter. I simply declare them and add their picture box to the controls on the main form. However I am hoping to have a sub routine inside the class that triggers whenever the timer in the main form ticks. I thought of something like this:
Public Class Jimmy
Dim _a As Integer = 10
Sub decreseNum(sender As Object, e As EventArgs) Handles mainapp.tmrLog.Tick
_a -= 1
End Sub
End Class
with mainapp being the name of the main form and tmrLog being the timer I want to associate my sub routine with. However the above code doesn't work
You could try defining a local reference to the timer in the Jimmy class:
Public Class Jimmy
Dim _a As Integer = 10
Private WithEvents tmr As Timer
Public Sub New(ByRef MainTmr As Timer)
tmr = MainTmr
End Sub
Sub decreseNum(sender As Object, e As EventArgs) Handles tmr.Tick
_a -= 1
End Sub
End Class
If you want all your classes react to timer.elapsed event, just sign up for it. The program below is fully operational. It is example what you can do to have your children to react to timer events of single parent/timer
Imports System
imports system.timers
Public Module Module1
Public Sub Main()
dim mc as new MainClass()
mc.CreateChildren(5)
System.Threading.Thread.Sleep(60000) ' wait and monitor output of childern
mc.Stop()
Console.WriteLine("All should stop now...")
Console.Read()
End Sub
End Module
public class MainClass 'This class could be your form
private _timer as new Timer(5000)
public sub CreateChildren(count as integer)
For i as integer = 1 to count
dim c as new Child(i)
Addhandler _timer.Elapsed, addressof c.DoWhentimerTicks
next
Console.WriteLine("timer should run now...")
_timer.Start()
end sub
public sub [Stop]()
_timer.Stop()
End Sub
End class
public class Child
private _myNO as integer
public sub new (no as integer)
_myNo = no
end sub
public sub DoWhentimerTicks(sender as object , e as ElapsedEventArgs)
Console.WriteLine(string.format("Child #{0} just ticked. Time = {1}", _myNo, e.signaltime))
end sub
End class
I found my solution, posting here for further reference.
My situation was trying to have my timer in the mainform triggering a sub in a class, and I used the following solution.
Class:
Sub addHandlesToSub
AddHandler Form1.Timer1.Tick, AddressOf subToBeTriggered
End Sub
Sub subToBeTriggered(sender As Object, e As EventArgs)
'My code
End Sub
The parameters in subToBeTriggered are useful when you want to remove the handler with
RemoveHandler Form1.Timer1.Tick, AddressOf subToBeTriggered
Otherwise, there will be an error without the parameters.
Thanks for all the answers though.
Public Class MainWindow
Private Sub MainWindow_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
Me.x(1)
End Sub
Public Sub x(ByVal x As String)
MessageBox.Show(x)
End Sub
End Class
If I want a Interface in sub x as example Public sub x(Byval IPerson) it also accept every type without an error.
In VS2013 under Debug/Debugging/Projects and Solutions/VB Defaults is an option to turn Option Strict to on.
Research tells me that raising an event from the constructor itself is not feasible as the object may not be fully initialised... so where can I fire an event from as soon as the constructor has fired?
One thing you can do is add a method to handle additional post ctor tasks:
Friend Class FooBar
Public Sub New
' your code here
End Sub
Public Sub Create
' do anything you want
End Sub
End Class
Elsewhere:
Friend WithEvents Foo As Foobar
' ...
Foo = New FooBar ' Foo doesnt exist until ctor code executes and the
' code returns to here.
Foo.Create ' do whatever you like, as long as any other
' objects referenced have been created.
The reason calling a sub from the ctor to raise an event wont work with a class is this:
Private Sub SomeEvent(sender As Object, e As EventArgs) Handles Foo.SomeEvent
Console.Beep()
End Sub
the key is Handles Foo.SomeEvent
There is no Foo yet to handle the event. It doesnt crash and there event is raised, but there is no object for the listener to catch/handle the event. Enough of a form is created in InitializeComponents, that it does work with a form.
There might also be an Interface to implement something like this, I know of some for Components, but not classes.
You could use the Load or Show events from the Shown.
Private Sub myForm_Shown(sender As Object, e As EventArgs) Handles Me.Shown
End Sub
or
Private Sub myForm_Load(sender As Object, e As EventArgs) Handles Me.Load
End Sub
You can accomplish this by adding an Action(Of T) parameter to your constructor and invoke the delegate on the very last line.
Public Class Foo
Public Sub New(ByVal action As Action(Of Foo))
'...
'...
'...
If (Not action Is Nothing) Then action.Invoke(Me)
End Sub
End Class
Example
Public Class Form1
Private Sub Button1_Click(sender As Object, ev As EventArgs) Handles Button1.Click
Dim foo1 As New Foo("foo1", AddressOf Me.HandleFooCtor)
Dim foo2 As New Foo("foo2", Sub(f As Foo) MessageBox.Show(f.Name))
End Sub
Private Sub HandleFooCtor(f As Foo)
MessageBox.Show(f.Name)
End Sub
Public Class Foo
Public Sub New(name As String, Optional ByVal action As Action(Of Foo) = Nothing)
'...
'...
'...
Me.Name = name
If (Not action Is Nothing) Then action.Invoke(Me)
End Sub
Public ReadOnly Name As String
End Class
End Class
I am having an issue when trying to delete ListView Items from a second form.
For example, if I use the following command on Form1 it works:
Listview1.SelectedItems(0).Remove
However, if I attempt to remove from Form2 like so:
Form1.Listview1.SelectedItems(0).Remove
I get the following error:
"Invalid argument=value of '0' is not valid for 'index'. Parameter name: index"
I then tried to get a count of items from the listview on Form2 and it gives me a return of 0
Form1.Listview1.Items.Count
I'm not sure what my problem is.
Update
I have posted a brief example of my code (using your suggestion as I can understand it):
frmShowMessages
Private Sub ViewMessage()
Dim frm As New frmViewMailMessage
frm.Show()
End Sub
Public Sub DeleteItem(ByVal index As Integer)
lsvReceivedMessages.Items(index).Remove()
End Sub
frmViewMessage
Private instanceForm as frmShowMessages
Private Sub frmViewMailMessage_Load(sender As Object, e As EventArgs) Handles MyBase.Load
instanceForm = New frmShowMessages()
End Sub
Private Sub cmdDelete_Click(sender As Object, e As EventArgs) Handles cmdDelete.Click
instanceForm.DeleteItem(_index)
End Sub
Hopefully my code can help identify where my issue is.
In VB.net usually you get a default Form instance for each of your Form. Probably you are creating an instance of Form1 and then you are trying to access ListView1 of default instance.
E.g.
Sub ButtonClick()
Dim f As New Form1()
f.Show()
' at this point if you access f's ListView you will get correct count
f.ListView1.Items.Count
' however if you try to access default instance it will NOT have any item
Form1.ListView.Items.Count
End Sub
It means your instance f is NOT equal to default Form1 instance.
Solution can be, make the f variable as class level variable and use it everywhere. Or if Form1 will have only 1 instance, then you can use the default instance everywhere.
Personally I would NOT go with direct control accessing over forms. I would create a Public method which should return the data as list to the caller, in this case your Form2.
UPDATED-2:
As per your given scenario, I am simplifying things for you, and doing implementation using Event.
Public Class frmShowMessages
Private Sub btnOpenMessage_Click(sender As System.Object, e As System.EventArgs) Handles btnOpenMessage.Click
Dim frmView As New frmViewMessage(Me.ListView1.SelectedItems(0).Index)
AddHandler frmView.MessageDeleted, AddressOf DeleteMessageHandler
frmView.Show()
End Sub
Private Sub DeleteMessageHandler(sender As Object, e As frmViewMessage.MessageDeletedEventArgs)
Me.ListView1.Items.RemoveAt(e.MessageIndex)
End Sub
End Class
Public Class frmViewMessage
' a class which will be used for Event communication
Public Class MessageDeletedEventArgs
Inherits EventArgs
Public Property MessageIndex As Integer
Public Sub New(ByVal iIndex As Integer)
MyBase.New()
Me.MessageIndex = iIndex
End Sub
End Class
' main event which will alert the parent that a message deletion should be done
Public Event MessageDeleted As EventHandler(Of MessageDeletedEventArgs)
' private variable that will hold the MessageIndex
Private Property MessageIndex As Integer
' method that is responsible to raise event
Protected Overridable Sub OnMessageDeleted()
RaiseEvent MessageDeleted(Me, New MessageDeletedEventArgs(Me.MessageIndex))
End Sub
' we want to create this Form using the MessageIndex of ListView
Public Sub New(ByVal iMessageIndex As Integer)
Me.InitializeComponent()
Me.MessageIndex = iMessageIndex
End Sub
' the delete button will raise the event to indicate parent that
' a deletion of message should be done
Private Sub btnDelete_Click(sender As System.Object, e As System.EventArgs) Handles btnDelete.Click
Me.OnMessageDeleted()
End Sub
End Class
One way or another I need to link groupID (and one other integer) to the button I am dynamically adding.. any ideas?
What I can do;
AddHandler mybutton.Click, AddressOf PrintMessage
Private Sub PrintMessage(ByVal sender As System.Object, ByVal e As System.EventArgs)
MessageBox.Show("Dynamic event happened!")
End Sub
What I can't do, but want to;
AddHandler mybutton.Click, AddressOf PrintMessage(groupID)
Private Sub PrintMessage(ByVal groupID as Integer)
MessageBox.Show("Dynamic event happened!" & groupID .tostring)
End Sub
There is no way to do this with AddressOf itself. What you're looking for is a lambda expression.
AddHandler myButton.Click, Function(sender, e) PrintMessage(groupId)
Private Sub PrintMessage(ByVal groupID as Integer)
MessageBox.Show("Dynamic event happened!" & groupID .tostring)
End Sub
You can create your own button class and add anything you want to it
Public Class MyButton
Inherits Button
Private _groupID As Integer
Public Property GroupID() As Integer
Get
Return _groupID
End Get
Set(ByVal value As Integer)
_groupID = value
End Set
End Property
Private _anotherInteger As Integer
Public Property AnotherInteger() As Integer
Get
Return _anotherInteger
End Get
Set(ByVal value As Integer)
_anotherInteger = value
End Set
End Property
End Class
Since VB 2010 you can simply write
Public Class MyButton
Inherits Button
Public Property GroupID As Integer
Public Property AnotherInteger As Integer
End Class
You can access the button by casting the sender
Private Sub PrintMessage(ByVal sender As Object, ByVal e As EventArgs)
Dim btn = DirectCast(sender, MyButton)
MessageBox.Show( _
String.Format("GroupID = {0}, AnotherInteger = {1}", _
btn.GroupID, btn.AnotherInteger))
End Sub
These new properties can even be set in the properties window (under Misc).
The controls defined in the current project automatically appear in the toolbox.
Use the Tag property of the button.
Button1.Tag = someObject
AddressOf gets the address of a method, and thus you cannot pass parameters to it.
You can use delegate which very clear for your code follow as:
Define a delegate
Public Delegate Sub ControlClickDelegate(ByVal sender As Object, ByVal e As EventArgs)
Custom button class
Public Class CustomButton
Inherits System.Windows.Forms.Button
#Region "property delegate"
Private controlClickDelegate As ControlClickDelegate
Public Property ClickHandlerDelegate As ControlClickDelegate
Get
Return controlClickDelegate
End Get
Set(ByVal Value As ControlClickDelegate)
controlClickDelegate = Value
End Set
End Property
#End Region
Public Sub RegisterEventHandler()
AddHandler Me.Click, AddressOf OnClicking
End Sub
Private Sub OnClicking(ByVal sender As Object, e As System.EventArgs)
If (Me.controlClickDelegate IsNot Nothing) Then
Me.controlClickDelegate(sender, e)
End If
End Sub
End Class
MainForm
Public Class MainForm
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Me.CusButton1.ClickHandlerDelegate = AddressOf Me.btnClick
Me.CusButton1.RegisterEventHandler()
End Sub
Private Sub btnClick(ByVal sender As Object, ByVal e As EventArgs)
Me.TextBox1.Text = "Hello world"
End Sub
End Class
The below worked for me:
Dim bStart = New Button With {.Text = "START"}
AddHandler bStart.Click, Function(sender, e) TriggerProcess(any Long value)
Private Function TriggerProcess(ByVal paramName As Long) As Boolean
' any processing logic
Return True
End Function
My solution:
AddHandler menuItemYear.Items(i).MouseUp, Sub() menu_year(2019)
Private Sub menu_year(ByVal intYear As Integer)
'do something
End Sub
There are few ways to do that depending of the complexity and number of parameters required.
1. Use Tag for adding a complex structure
2. Inherit the the Button class and add the values as class members then populate them before using it. That gives you a lot more flexibility.
If you are using web version
3. You cannot add it to Tag, but for simple values assign it to index use .Attributes.Add("name"). This gets added to the HTML tags and not the Server side. You can then use the index to access a server side structure for complex systems.
4. Use sessions to store values and store the session reference to Name attribute as described above (#3).
No problem ;-)
For example:
Private ComboActionsOnValueChanged As New Dictionary(Of ComboBox, EventHandler)
'somewhere in function
dim del = Sub(theSender, eventArgs)
MsgBox(CType(theSender, ComboBox).Name & " test")
End Sub
ComboActionsOnValueChanged.Add(myCombo, del)
'somewhere else
Dim delTest = ComboActionsOnValueChanged(myCombo)
RemoveHandler myCombo.SelectedValueChanged, delTest
myCombo.DataSource = someDataSource
AddHandler myCombo.SelectedValueChanged, delTest
as we expect, event won't fire after DataSource change in this place