How do I avoid an event from being handled twice (if is the same handler?)
Module Module1
Sub Main()
Dim item As New Item
AddHandler item.TitleChanged, AddressOf Item_TitleChanged
AddHandler item.TitleChanged, AddressOf Item_TitleChanged
item.Title = "asdf"
Stop
End Sub
Private Sub Item_TitleChanged(sender As Object, e As EventArgs)
Console.WriteLine("Title changed!")
End Sub
End Module
Public Class Item
Private m_Title As String
Public Property Title() As String
Get
Return m_Title
End Get
Set(ByVal value As String)
m_Title = value
RaiseEvent TitleChanged(Me, EventArgs.Empty)
End Set
End Property
Public Event TitleChanged As EventHandler
End Class
Output:
Title changed!
Title changed!
Desired output:
Title changed!
I want the event manager to detect that this event is already handled by this handler and so it shouldn't rehandle (or readd) it.
You can also just always call RemoveHandler before AddHandler. I have found this practical in specific scenarios.
Wrapping the event handler list in a HashSet will make sure the handlers are not duplicate references, the following snippet replacement for the question's Item class will work under the above sample (it won't re-add the handler if it's already in the HashSet):
Public Class Item
Private m_Title As String
Public Property Title() As String
Get
Return m_Title
End Get
Set(ByVal value As String)
m_Title = value
RaiseEvent TitleChanged(Me, EventArgs.Empty)
End Set
End Property
Private handlers As New HashSet(Of EventHandler)
Public Custom Event TitleChanged As EventHandler
AddHandler(value As EventHandler)
handlers.Add(value)
End AddHandler
RemoveHandler(value As EventHandler)
handlers.Remove(value)
End RemoveHandler
RaiseEvent(sender As Object, e As System.EventArgs)
For Each handler In handlers.Where(Function(h) h IsNot Nothing)
handler(sender, e)
Next
End RaiseEvent
End Event
End Class
Related
I have a class that allows ToolStrip to have a NumericUpDown. I added a properties (Value, Minimum and Maximum). It is working but I want to remove the Text property since I added the Value property. Is there a way to do this?
Please see image where you can see the designer properties
Below is the class
<Windows.Forms.Design.ToolStripItemDesignerAvailabilityAttribute(Windows.Forms.Design.ToolStripItemDesignerAvailability.ToolStrip), DebuggerStepThrough()>
Public Class ToolStripNumericUpDown
Inherits Windows.Forms.ToolStripControlHost
Public Sub New()
MyBase.New(New System.Windows.Forms.NumericUpDown())
End Sub
Public ReadOnly Property ToolStripNumericUpDownControl() As Windows.Forms.NumericUpDown
Get
Return TryCast(Control, Windows.Forms.NumericUpDown)
End Get
End Property
Public Property Value() As Long
Get
Return ToolStripNumericUpDownControl.Value
End Get
Set(ByVal value As Long)
ToolStripNumericUpDownControl.Value = value
End Set
End Property
Public Property Minimum() As Long
Get
Return ToolStripNumericUpDownControl.Minimum
End Get
Set(ByVal value As Long)
ToolStripNumericUpDownControl.Minimum = value
End Set
End Property
Public Property Maximum() As Long
Get
Return ToolStripNumericUpDownControl.Maximum
End Get
Set(ByVal value As Long)
ToolStripNumericUpDownControl.Maximum = value
End Set
End Property
Protected Overrides Sub OnSubscribeControlEvents(ByVal c As Windows.Forms.Control)
MyBase.OnSubscribeControlEvents(c)
AddHandler DirectCast(c, Windows.Forms.NumericUpDown).ValueChanged, AddressOf OnValueChanged
End Sub
Protected Overrides Sub OnUnsubscribeControlEvents(ByVal c As Windows.Forms.Control)
MyBase.OnUnsubscribeControlEvents(c)
RemoveHandler DirectCast(c, Windows.Forms.NumericUpDown).ValueChanged, AddressOf OnValueChanged
End Sub
Public Event ValueChanged As EventHandler
Private Sub OnValueChanged(ByVal sender As Object, ByVal e As EventArgs)
RaiseEvent ValueChanged(Me, e)
End Sub
End Class
I'm just getting started with custom classes so I wrote a button strip. It inherits a panel and populates it with buttons from strings passed to my .Add().
ButtonStrip1.Add("Button","Texts","Go Here")
I'd like for it to be able to naturally grab ButtonStrip1.Click's handler and pass it on to child buttons and delete it from ButtonStrip1.
I haven't been able to figure that out, so I've been doing
Public Class ButtonStrip
Inherits Panel
Public Property Innermargin As Integer = 5
Dim Offset As Integer = Innermargin
Dim Buttons = New List(Of ButtonStrip_Button)
Dim StoredFN As EventHandler
Public Sub New()
End Sub
Function Add(fn As EventHandler, ParamArray ByVal Values As String())
StoredFN = fn
For Each V In Values
Dim B As New ButtonStrip_Button
Buttons.Add(B)
Me.Controls.Add(B)
B.Text = V
B.Left = Offset + Innermargin
B.Top = Innermargin
Offset = B.Left + B.Width
AddHandler B.Click, fn
Next
RemoveHandler Me.Click, fn
Me.Width = Offset + Innermargin
Me.Height = Buttons(0).height + Innermargin * 2
End Function
Function Add(ParamArray ByVal Values As String())
If StoredFN Is Nothing Then
Throw New Exception("First Add() must supply a function")
End If
Me.Add(StoredFN, Values)
End Function
End Class
Public Class ButtonStrip_Button
Inherits System.Windows.Forms.Button
Public Sub New()
AutoSize = True
AutoSizeMode = AutoSizeMode.GrowAndShrink
End Sub
End Class
which is called by
ButtonStrip1.Add(AddressOf ButtonStrip1_Click,"Button","Texts","Go Here")
What I'd basically like to do is (psuedo-code)
Function Add(fn As EventHandler, ParamArray ByVal Values As String())
If StoredFN is Nothing Then StoredFN = Me.Click
...
AddHandler B.Click, Me.Click
Next
RemoveHandler Me.Click, Me.Click
...
End Function
I've tried changing a few things and googled a lot. I've also tried using CallByName(Me,"Click",CallType.Method) and with CallType.Get, but the error I get is Expression 'Click' is not a procedure, but occurs as the target of a procedure call. It also returns this exact same message for unhandled events, such as ButtonStrip1 has no MouseDown Event.
I've also tried using MyClass.
Not seen here is an alternative .Add() that add StoredFN to B.click
For instance, this click event works with my code
Private Sub ButtonStrip1_Click(sender As Object, e As EventArgs) Handles ButtonStrip1.Click
msgbox("You clicked " & sender.text & ".")
End Sub
What I was suggesting was something like this:
Public Class ButtonStrip
Inherits Panel
Public Event ButtonClick As EventHandler(Of ButtonClickEventArgs)
Protected Overridable Sub OnButtonClick(e As ButtonClickEventArgs)
RaiseEvent ButtonClick(Me, e)
End Sub
Private Sub Buttons_Click(sender As Object, e As EventArgs)
OnButtonClick(New ButtonClickEventArgs(DirectCast(sender, Button)))
End Sub
Public Sub Add(ParamArray values As String())
Dim btn As New Button
AddHandler btn.Click, AddressOf Buttons_Click
'...
End Sub
End Class
Public Class ButtonClickEventArgs
Inherits EventArgs
Public ReadOnly Property Button As Button
Public Sub New(button As Button)
Me.Button = button
End Sub
End Class
Now there's no need to pass event handlers around. When a Button is clicked, the ButtonStrip handles that event and then raises its own ButtonClick event. Neither the ButtonStrip nor the Buttons have to care about any methods that handle that event as it will be handled the same way any other event is. In a form, you'd then handle the ButtonClick event of the ButtonStrip and get the Button that was clicked from e.Button. You could also add an Index property if you wanted to know the position of the Button rather than the Button itself.
I have been trying to get a label to databind to a readonly property. I have a much more complex project which I am implementing this in and it isn't working. I have been unsuccessful in getting help with this so I have created a much simpler version of the project and my databinding still isn't updating.
To replicate my issue you will need a form with a textbox, label and button, and then a class.
The code for the class is as follows
Imports System.ComponentModel
Public Class databinding
Implements INotifyPropertyChanged
Public Sub New()
numbers = New List(Of number)
End Sub
Public Property numbers As List(Of number)
Get
Return m_number
End Get
Set(value As List(Of number))
m_number = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("hnumber"))
End Set
End Property
Private m_number As List(Of number)
Public ReadOnly Property hnumber As Integer
Get
Dim list As IList(Of number) = (From t As number In numbers Select t Order By t.value Descending).ToList()
If (list.Count > 0) Then
If (IsNothing(list(0).value)) Then
Return "0"
Else
Return list(0).value
End If
End If
Return "0"
End Get
End Property
Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
End Class
Public Class number
Public Property value As Integer
Get
Return t_number
End Get
Set(value As Integer)
t_number = value
End Set
End Property
Private t_number As Integer
End Class
The code for the form is as follows:
Public Class Form1
Public numberlist As New databinding
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Label1.DataBindings.Add(New Binding("text", numberlist, "hnumber"))
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim newnum As New number
newnum.value = TextBox1.Text
numberlist.numbers.Add(newnum)
End Sub
End Class
Now based on my understanding when you click the button a number from the textbox is added to this list, which happens, and the hnumber value updates, which using a breakpoint and a watch I can see also happens. From reading I need to implement inotifypropertychanged when I set the new number to get the label to re check the databind (which has been done).
However the label will stay at 0. If I run watch through Label1 I can see that under DataBindings > List > arrayList > (0) > System.Windows.Forms.Binding>DataSource>Databinding_test.databinding the details of the class (including the correct value for hnumber) is listed, so to me that shows that the Label does in fact know about the value it should be binding to.
Could someone please fill me in on what I am missing to make this all work, as it is almost causing me to pull out all of my hair.
Thanks,
mtg
I've tried to explain this to you before, and I will again.
The reason why your binding isn't updated is because you're adding the value to a list.
numberlist.numbers.Add(newnum)
However, if you "change" the list, this will trigger the propertychanged event.
numberlist.numbers.Add(newnum)
numberlist.numbers = numberlist.numbers '<--
Instead of using an IList<T> you should use the ObservableCollection<T> which allows you to track the changes made.
Public Class databinding
Implements INotifyPropertyChanged
Public Sub New()
Me.numbers = New ObservableCollection(Of number)
End Sub
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Property numbers As ObservableCollection(Of number)
Get
Return m_number
End Get
Set(value As ObservableCollection(Of number))
If (Not m_number Is value) Then
Unhook(m_number)
Hook(value)
m_number = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("hnumber"))
End If
End Set
End Property
Public ReadOnly Property hnumber As Integer
Get
If (Not numbers Is Nothing) Then
Dim list As IList(Of number) = (From t As number In numbers Select t Order By t.value Descending).ToList()
If (list.Count > 0) Then
If (IsNothing(list(0).value)) Then
Return 0
Else
Return list(0).value
End If
End If
End If
Return 0
End Get
End Property
Private Sub Hook(collection As ObservableCollection(Of number))
If (Not collection Is Nothing) Then
AddHandler collection.CollectionChanged, AddressOf Me.OnNumbersChanged
End If
End Sub
Private Sub OnNumbersChanged(sender As Object, e As NotifyCollectionChangedEventArgs)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("hnumber"))
End Sub
Private Sub Unhook(collection As ObservableCollection(Of number))
If (Not collection Is Nothing) Then
RemoveHandler collection.CollectionChanged, AddressOf Me.OnNumbersChanged
End If
End Sub
Private m_number As ObservableCollection(Of number)
End Class
Public Event DocumentCompleted As WebBrowserDocumentCompletedEventHandler
Dim arg() As Object = {homeTeam, guestTeam}
AddHandler browser.DocumentCompleted, New
WebBrowserDocumentCompletedEventHandler(AddressOf DoStuff)
Private Sub DoStuff(ByVal sender As Object, ByVal e As WebBrowserDocumentCompletedEventArgs)
End Sub
How can I pass the homeTeam and guestTeam when firing the DocumentCompleted event.
I want to ge the above to values to inside the Dostuff method.
Please help.
First of all, you cannot have this hanging in the middle of nowhere:
Dim arg() As Object = {homeTeam, guestTeam}
AddHandler browser.DocumentCompleted,
New WebBrowserDocumentCompletedEventHandler(AddressOf DoStuff)
AddHandler probably needs to be in some Initialize method, which could be inside Sub New, after InitializeComponent, or inside Form_Load, or as soon as you expect it to be triggered (after a specific event). Notice here that you are using a default event of a native .NET component, with a default event type. In this case you cannot directly consume anything other than what it already provides, when triggered. See WebBrowser.DocumentCompleted Event on MSDN.
You can, however, override all relevant classes and have your own MyWebBrowser control and your own event, with would contain additional properties. See below example:
Public Class Form1
Sub New()
' This call is required by the designer.
InitializeComponent()
Dim browser As New MyWebBrowser
AddHandler browser.MyDocumentCompleted, AddressOf DoStuff
End Sub
Private Sub DoStuff(ByVal sender As Object, ByVal e As MyWebBrowserDocumentCompletedArgs)
Dim guestTeam As String = e.GuestTeam 'guest team
Dim homeTeam As String = e.HomeTeam 'and home team are both accessible
'so you can do some processing on them
End Sub
Public Class MyWebBrowserDocumentCompletedArgs : Inherits WebBrowserDocumentCompletedEventArgs
Dim _homeTeam As String
Dim _guestTeam As String
Public ReadOnly Property HomeTeam
Get
Return _homeTeam
End Get
End Property
Public ReadOnly Property GuestTeam
Get
Return _guestTeam
End Get
End Property
Sub New(url As Uri, homeTeam As String, guestTeam As String)
MyBase.New(url)
_homeTeam = homeTeam
_guestTeam = guestTeam
End Sub
End Class
Public Class MyWebBrowser : Inherits WebBrowser
Public Delegate Sub MyWebBrowserDocumentCompletedEventHandler(e As MyWebBrowserDocumentCompletedArgs)
Public Event MyDocumentCompleted As MyWebBrowserDocumentCompletedEventHandler
Protected Overrides Sub OnDocumentCompleted(e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs)
MyBase.OnDocumentCompleted(e)
'homeTeam and guestTeam need to be extracted from the current instance of MyWebBrowser, and passed further
RaiseEvent MyDocumentCompleted(New MyWebBrowserDocumentCompletedArgs(e.Url, "homeTeam", "guestTeam"))
End Sub
End Class
End Class
If your project is relatively small, you can indeed have those as global variables, as #Vlad suggested in the comments.
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