I have public class, with event declared in it.
And have procedure which shows modal form.
The form has buttons, on whichs click I want the main event to be raised. How to achieve this?
for example:
Public class MyClass
Public Event MyEvent(arg as date)
Public Sub ShowForm()
using frm as new frmMyForm
frm.showDialog()
End Using
....
End Class
On forms button click event
RaiseEvent MyClass.MyEvent(Today)
I have passed egzemplar of class as property, but nothing helped.
I have solved problem. I have really created method in the main class with date parameter. In button click I'm calling above method of passed egzemplar with desired argument. and then raising event in a class. it works fine now.
In my situation code is more harder, therefore I provide only a simple example instead.
Public class MyClass
Public Event MyEvent(arg as date)
Public sub FromOtherPlanet(dt as Date)
RaiseEvent MyEvent(dt)
End sub
Public Sub ShowForm()
using frm as new frmMyForm
frm.Egz = Me
frm.showDialog()
End Using
End Sub
....
End Class
in the form
Public class MyForm
dim Temp_Egz as MyClass
public property Egz as Myclass
Get
.......
Set
....
End Property
private sub button1_click.....
egz.FromOtherPlanet(today)
end sub
end class
Related
I have a weird problem that I can't wrap my head around.
I have the following code:
Public Class Form1
Public WithEvents MyClass1 As New MyClass
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Private Sub MyClass_UpdateListbox() Handles MyClass1.UpdateListbox
For Each sItem as String In MyClass1.Listbox
MsgBox(sItem) 'an MsgBox shows correct items each time.
Next sItem
Me.Listbox = Me.MyClass1.Listbox 'doesn't work and breaks listbox.
Me.Listbox.Items.Clear() 'listbox is empty anyway, but has no effect.
Me.Listbox.Items.Add("event triggered") 'does nothing.
End Sub
End Class
Public Class MyClass
Public Listbox as new Listbox
Public Event UpdateListbox()
Public Sub New()
'Constructor. sub.
Me.AddItem("Populating listbox")
End Sub
Public Sub AddItem(sItem as String)
Me.Listbox.Items.Add(sItem)
RaiseEvent UpdateListbox()
End Sub
End Class
If I comment the following lines in above code, the listbox keeps adding event triggered, as expected. Of course, I don't have to remove the clear one. It will work, but then it just adds the same item. If I use a command button and call MyClass.AddItem("Something") that is correctly added too as long as the below is commented out. But if not, then once the listbox is in broken state, nothing can be added anymore.
Me.Listbox = Me.MyClass1.Listbox 'doesn't work and breaks listbox.
Me.Listbox.Items.Clear() 'listbox is empty anyway, but has no effect.
How can I use a virtual listbox and assign it to my real listbox?
Also, instead of assigning one listbox to the other, I can of course use that for each loop and add each item one by one which works, but that for each look was for debugging purpose in the first place.
EDIT:
My goal with this application is to build a Todo list with features that are not in a todolist. This is a project I build for work because there I need a tool like this. I already have a todolist that I use but I built it wrong in the past. Everything was condensed in form1, no modules no extra classes. As a result I got weird bugs that I patched with workarounds. I am now rebuilding the application from the ground up, separating tasks in its own classes so I can apply business logic and have a true OOP application. The todo list will become its own class, and managing the list etc will be handeled by this class. It interacts with controls on the form, such as buttons and listboxes. If I just use form1.listbox from the class, things break at program start. I started another question and the below code was a now deleted answer. At first I did not get it working because I did not realize the listbox crashes if I assign it the virtual instance.
So my goal is to have the todolist be handled entirely by the todolist class. It does need a way to interact with controls on form1, and that is the puzzle I'm currently trying to solve.
In the original code, the main problem is that the Field that hold the instance of a Control shown if a Form is reassigned to the instance of another ListBox Control defined in a custom class:
Me.Listbox = Me.MyClass1.Listbox
From now on, Me.Listbox points another ListBox that is not show on screen, so any attempt to update the Form's child ListBox fails, except when Me.Listbox.Items.Clear() is called - in the same procedure - after it's being reassigned, because the handle of the Owner of the ObjectCollection (the object that holds the Items shown in the ListBox) has not been updated yet. It's going to fail after the current method exits nonetheless.
As noted in comments, this is a simplified method to handle a Form and its child Controls using a handler class. The contract between the class handler and a Form is sealed by an Interface (named IFormHandler here).
A Form that implements this Interface exposes the methods defined by the Interface that allow to trigger Actions and specific behaviors, depending on the Type of Control and the implementation.
I suggest to take a look at the MVP or ReactiveUI (MVVM-derived) for WinForms Patterns.
How too proceed:
Open up the ApplicationEvents class object.
If you don't have it already, select Project -> Properties -> Application and click the View Application Events button. It will generate ApplicationEvents.vb. Find it in Solution Explorer and open it up.
It should look like this (plus a bunch of comments that explain what it's for):
Imports Microsoft.VisualBasic.ApplicationServices
Namespace My
Partial Friend Class MyApplication
End Class
End Namespace
Paste into MyApplication these lines of code:
Imports Microsoft.VisualBasic.ApplicationServices
Namespace My
Partial Friend Class MyApplication
Public SomeFormHandler As MyFormHandler(Of SomeForm)
Protected Overrides Function OnStartup(e As StartupEventArgs) As Boolean
SomeFormHandler = New MyFormHandler(Of SomeForm)
Return MyBase.OnStartup(e)
End Function
End Class
End Namespace
Add an Interface that defines the Actions (or Behaviors) that a Form must implement.
Here, the GetUsersList() method specifies that a Form that implements this Interface must return the instance of a child ListBox Control.
(To add an Interface, select Project -> Add -> New Item... and select the Interface template. Name the file IFormHandler)
Extend this Interface as needed, to add more Methods or Properties that define actions and behaviors.
Public Interface IFormHandler
Function GetUsersList() As ListBox
End Interface
A Form that implements the IFormHandler Interface implements and exposes the GetUsersList() method, which returns the instance of a ListBox Control (named usersList here)
There's nothing else to do with this Form, the control is handed over to the MyFormHandler object that is initialized with this Type.
Public Class SomeForm
Implements IFormHandler
Public Sub New()
InitializeComponent()
End Sub
Public Function GetUsersList() As ListBox Implements IFormHandler.GetUsersList
Return Me.usersList
End Function
End Class
Now, to show SomeForm, you can use the MyFormHandler class object show below.
' Set the Owner if called from another Form
My.Application.SomeFormHandler.Show(Me)
' Or without an Owner
My.Application.SomeFormHandler.Show()
To close SomeForm, you can either use its handler:
My.Application.SomeFormHandler.Close()
or close it as usual:
[SomeForm Instance].Close()
If MyFormHandler determines that the instance of SomeForm has been disposed, it creates a new one when you call its Show() method again later.
To update the ListBox Control of SomeForm, use the public methods exposed by the MyFormHandler class:
' Add a new element
My.Application.SomeFormHandler.UpdateUsersList(UpdateType.AddElement, "Some Item")
' Remove an element
My.Application.SomeFormHandler.UpdateUsersList(UpdateType.RemoveElement, "Some Item")
' Replace an element
My.Application.SomeFormHandler.UpdateUsersList(UpdateType.ReplaceElement, "New Item", "Some Item")
' Clears the ListBox
My.Application.SomeFormHandler.ClearUsersList()
All these actions generate an event that you can subscribe to when needed.
See also the example that shows how to raise a custom event when the ListBox raises one of its stardard events; SelectedIndexChanged is handled here.
See the implementation of MyFormHandler.
Generic Form handler:
A Form needs to implement the IFormHandler Interface for the MyFormHandler class to accept it as valid.
You can of course extend the Interface, to add more Actions, or build a MyFormHandler class object that uses a different Interface, or more than one.
Public Class MyFormHandler(Of TForm As {Form, IFormHandler, New})
Implements IDisposable
Private formObject As TForm
Private IsInstanceSelfClosing As Boolean = False
Public Event UsersListUpdate(item As Object, changeType As UpdateType)
Public Event UsersListIndexChanged(index As Integer)
Public Sub New()
InitializeInstance()
Dim lstBox = formObject.GetUsersList()
AddHandler lstBox.SelectedIndexChanged, AddressOf OnUsersListIndexChanged
End Sub
Private Sub InitializeInstance()
formObject = New TForm()
AddHandler formObject.FormClosing, AddressOf OnFormClosing
End Sub
Private Sub OnFormClosing(sender As Object, e As FormClosingEventArgs)
IsInstanceSelfClosing = True
Dispose()
End Sub
Public Sub UpdateUsersList(updateMode As UpdateType, newItem As Object, Optional oldItem As Object = Nothing)
If newItem Is Nothing Then Throw New ArgumentException("New Item is null")
Dim lstBox = formObject.GetUsersList()
Select Case updateMode
Case UpdateType.AddElement
lstBox.Items.Add(newItem)
Case UpdateType.RemoveElement
lstBox.Items.Remove(newItem)
Case UpdateType.ReplaceElement
If oldItem Is Nothing Then Throw New ArgumentException("Replacement Item is null")
Dim index = lstBox.Items.IndexOf(oldItem)
lstBox.Items.Remove(oldItem)
lstBox.Items.Insert(index, newItem)
Case Else : Return
End Select
RaiseEvent UsersListUpdate(newItem, updateMode)
End Sub
Public Sub ClearUsersList()
formObject.GetUsersList().Items.Clear()
End Sub
Private Sub OnUsersListIndexChanged(sender As Object, e As EventArgs)
RaiseEvent UsersListIndexChanged(DirectCast(sender, ListBox).SelectedIndex)
End Sub
Public Sub Show(Optional owner As IWin32Window = Nothing)
If formObject Is Nothing OrElse formObject.IsDisposed Then InitializeInstance()
If formObject.Visible Then
formObject.WindowState = FormWindowState.Normal
formObject.BringToFront()
Else
formObject.Show(owner)
End If
End Sub
Public Sub Close()
If formObject IsNot Nothing AndAlso (Not formObject.IsDisposed) Then
RemoveHandler formObject.FormClosing, AddressOf OnFormClosing
IsInstanceSelfClosing = False
Dispose()
End If
End Sub
Public Sub Dispose() Implements IDisposable.Dispose
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
Protected Overridable Sub Dispose(disposing As Boolean)
If disposing Then
If formObject Is Nothing OrElse formObject.IsDisposed Then Return
Dim lstBox = formObject.GetUsersList()
RemoveHandler lstBox.SelectedIndexChanged, AddressOf OnUsersListIndexChanged
RemoveHandler formObject.FormClosing, AddressOf OnFormClosing
If Not IsInstanceSelfClosing Then formObject.Close()
IsInstanceSelfClosing = False
End If
End Sub
End Class
Enumerator used in MyFormHandler:
Public Enum UpdateType
AddElement
RemoveElement
ReplaceElement
End Enum
what is the correct way to call function outside the class, below code is also working
tried an alternate way by using delegate but couldn't figure out to pass function with parameters from Form class to classname so that form function can be called.
Public class form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
dim cl as new classname
cl.run()
end sub
function testmsg(txt as string)
msgbox(txt)
end function
end class
public class classname
public sub run()
txt = "xyz"
if(condition = true) then call form1.testmsg(byref txt as string)
end sub
end class
You can at any time, and in any place, and from a form, a class object, or even just standard vb module call/use a function (or in your case, it should be a sub).
Just mark any routine (sub/function) in the form as public.
eg:
Public function testmsg(txt as string)
msgbox(txt)
end function
NOw, in any other form, class or in fact any place you have code, you can thus go:
FormA.TestMsg("hi from form B")
so, there are no restrictions here. And any form wide scoped variables marked as public can also be used:
eg:
Public Class FormA
Public Zoo As String
Public Function TestMsg(txt As String)
MsgBox(txt)
End Function
Public Sub ShowZoo()
MsgBox("value of zoo = " & Zoo)
End Sub
End Class
So above is FormA
Now, any code from any ohter form, class or whatever can do this:
FormA.TestMsg("hi from form B")
FormA.Zoo = "this is zoo value"
FormA.ShowZoo()
So, just mark any variable as public (it in effect becomes a public property of that form).
And, just mark any function/Sub as pubic (it in effect becomes a public "method" of that form.
I'm using the base class Button in VB.net (VS2017) to create a new class called CDeviceButton. The CDeviceButton then forms as a base for other classes such as CMotorButton, CValveButton.
I want to set the Tag property in the child class CMotorButton but access it in the constructor in CDeviceButton. Doesn't work for me. It turns up being empty.
The Tag is set in the standard property when inserting the CMotorButtom instance into a form.
I've also tried to ensure teh the parent classes' constructors are run by setting mybase.New() as the first action in each constructor but that didn't change anything.
Any ideas for improvements?
Public Class CDeviceButton
Inherits Button
Public MMIControl As String = "MMIC"
Public Sub New()
MMIControl = "MMIC" & Tag
End Sub
End class
Public Class CMotorButton
Inherits CDeviceButton
Sub New()
'Do Something
end Sub
End Class
When you try to concatenate Tag with a string, you are trying to add an object that is probably nothing. I set the Tag property first and used .ToString and it seems to work.
Public Class MyButton
Inherits Button
Public Property MyCustomTag As String
Public Sub New()
'Using an existing Property of Button
Tag = "My Message"
'Using a property you have added to the class
MyCustomTag = "Message from MyCustomTag property : " & Tag.ToString
End Sub
End Class
Public Class MyInheritedButton
Inherits MyButton
Public Sub New()
If CStr(Tag) = "My Message" Then
Debug.Print("Accessed Tag property from MyInheritedButton")
Debug.Print(MyCustomTag)
End If
End Sub
End Class
And then in the Form
Private Sub Test()
Dim aButton As New MyInheritedButton
MessageBox.Show(aButton.Tag.ToString)
MessageBox.Show(aButton.MyCustomTag)
End Sub
Below is my solution I came up with that works. Basically I make sure that all initialization has taken place before reading the Tag property. What I experienced is that the Tag property is empty until the New() in CMotorButton has completed, even though the Tag property has been set when creating the instance of CMotorButton in the Form. TimerInitate has a Tick Time of 500 ms.
Not the most professional solution but works for what I need at the moment.
Another option could be multi threading but that I haven't tried and leave that for future tryouts.
Public Class CDeviceButton
Inherits Button
Public MMIControl As String = "MMIC"
Public Sub New()
TimerInitiate = New Timer(Me)
End Sub
Private Sub TimerInitiate_Tick(sender As Object, e As EventArgs) Handles TimerInitiate.Tick
If Tag <> Nothing Then
TimerInitiate.Stop()
MMIControl = "MMIC" & Tag
End If
End Sub
End class
Public Class CMotorButton
Inherits CDeviceButton
Sub New()
'Do Some stuff
TimerInitiate.Start()
End Sub
Private Sub CMotorButton_Click(sender As Object, e As EventArgs) Handles Me.Click
End Class
Update: I think it has something to do with lazy instantiation of the window handle for MainForm - but haven't been able to work out quite how that would result in the behavior seen here.
The application requests data via 3rd party COM interface providing a callback to process the results. In the callback, the UI needs to be updated - but the update doesn't work as expected. It's as if a value copy of MainForm had been created, when MainForm.DataReady is called or invoked directly cross thread, but UI update works as expected when executed from an event handler. Can you explain why?
(Note: AppDomain.CurrentDomain.Id is always 1 whether examined in MainForm or in ClassB.)
Initial Code - call to DataReady from ClassB instance without InvokeRequred /Delegate /Invoke logic in MainForm. Application UI change works as expected, MainForm SomeListControl.EmptyListMsg = "Not Available" change doesn't 'stick' (as if applied to a separate copy of MainForm)
Module AppGlobals
Public WithEvents A As ClassA
End Module
Partial Friend Class MyApplication
Private Sub MyApplication_Startup(ByVal sender As Object,
ByVal e As StartupEventArgs) Handles Me.Startup
A = New ClassA()
End Sub
End Class
Class MainForm
private sub getData
ToggleWait(True)
SomeListControl.Clear()
A.getData() 'Sets up the com object & callback
end sub
Public Sub DataReady()
ToggleWait(False)
' Do something with the data
End Sub
Private Sub ToggleWait(toggle as Boolean)
Application.UseWaitCursor = False
if toggle then
SomeListControl.EmptyListMsg = "Not Available"
else
SomeListControl.EmptyListMsg = "Please Wait"
end if
End Sub
End Class
Class ClassA
public sub getData()
Dim ComObj as New ComObject
Call ComObj.setClient(New ClassB)
End Sub
End Class
Class ClassB
Implements IComObjectClient
sub getdata_callback(results() as Object) handles IComObjectClient.getdata_callback
' Get the results
MainForm.DataReady()
end sub
End Class
Added InvokeRequred logic to DataReady, still called directly from ClassB. InvokeRequired is never true, Application UI change works as expected, MainForm SomeListControl.EmptyListMsg = "Not Available" change doesn't 'stick' (as if applied to a separate copy of MainForm)
Class MainForm
Public Delegate Sub DataReadyDelegate(ByVal toggle As Boolean)
...
Public Sub DataReady()
If InvokeRequired Then
Invoke(New DataReadyDelegate()
Else
ToggleWait(False)
' Do something with the data
End If
End Sub
...
End Class
Invoked MainForm.DataReady directly from ClassB Got exception: "Invoke or BeginInvoke cannot be called on a control until the window handle has been created." until I forced the window handle creation. Then it's the same behavior as before, namely, InvokeRequired is never true, Application UI change works as expected, MainForm SomeListControl.EmptyListMsg = "Not Available" change doesn't 'stick' (as if applied to a separate copy of MainForm)
Class ClassB
Implements IComObjectClient
Public Delegate Sub DataReadDelegate()
sub getdata_callback(results() as Object) handles IComObjectClient.getdata_callback
' Get the results
If Not MainForm.IsHandleCreated Then
' This call forces creation of the control's handle
Dim handle As IntPtr = MainForm.Handle
End If
MainForm.Invoke(New DataReadyDelegate(AddressOf MainForm.DataReady))
end sub
End Class
Executed from Event Handler Defined custom 'got data' events in ClassA and ClassB. ClassA listens for ClassB.got_data_event and raises ClassA.got_data_event, MainForm listens for ClassA.got_data_event and handles it by calling DataReady(). This works - InvokeRequired is true, Invoke is excuted, Application UI and MainForm UI changes work as intended.
Class MainForm
Public Delegate Sub DataReadyDelegate()
...
Public Sub DataReady()
If InvokeRequired Then
Invoke(New DataReadyDelegate()
Else
ToggleWait(False)
' Do something with the data
End If
End Sub
Public Sub _GotData_HandleEvent(ByVal resultMessage As String)
DataReady()
End Sub
Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles Me.Load
...
ToggleWait(False)
AddHandler A.GotData, AddressOf _GotData_HandleEvent
...
End Sub
...
End Class
Contrast:
A.getData()
with:
If Not MainForm.IsHandleCreated Then
You are using proper object-oriented programming syntax in the first statement. A is an object. The Form.IsHandleCreated property is an instance property, it requires an object name at the left side. You however used a type name. MainForm is not an object, it is a type in your code.
That this is possible is a very nasty VB.NET feature. It exists to help VB6 programmers move to VB.NET coding, VB6 strongly encouraged using the form's type name. Syntax inherited from VB1 before VB4 implemented anything resembling objects.
Now this is most certainly a convenience. You can refer to the form object in another class by simply using the type name. Note how you did not have that convenience with the A object. You solved it by making it a global variable, storing it in a Module. That doesn't win any prices either, but did allow you to reference A in any class.
Problem is, this convenience turns deadly when you start using the fake form object in another thread. What you didn't count on is that this object has <ThreadLocal> scope. In other words, when you use it in a worker thread then you get a new object of class MainForm. This form object is not visible, you never called its Show() method. Not that this would work, the thread does not pump a message loop so that form won't paint itself properly. Another side effect you observed is that its InvokeRequired property doesn't behave. It returns False. Correctly so, the form was created on the work thread so you don't actually have to use BeginInvoke(). Not that this would work either, it is still the wrong object, not the one that the user is looking at.
So one Q&D workaround is to do the same thing with the form object as you did with the A object, store it in a global variable:
Module AppGlobals
Public WithEvents A As ClassA
Public MainWindow As MainForm
End Module
And initialize it from the class constructor:
Class MainForm
Sub New()
InitializeComponent()
MainWindow = Me
End Sub
'' etc..
End Class
Now you can refer to MainWindow in your classes. And you get a reference to the actual instance of MainForm class that the user is looking at. And get the proper return value from MainWindow.InvokeRequired.
This will solve your problem, but it is still ugly and error prone. The right way looks like this:
Public Class MainForm
Private Shared MainWindow As MainForm
Public Shared ReadOnly Property Instance() As MainForm
Get
'' Return a reference to the one-and-only instance of MainForm
If MainWindow Is Nothing Then
'' It doesn't exist yet so create an instance
'' Creating one on a worker thread will never work, so complain
If System.Threading.Thread.CurrentThread.GetApartmentState() <> Threading.ApartmentState.STA Then
Throw New InvalidOperationException("Cannot create a window on a worker thread")
End If
New MainForm()
End If
Return MainWindow
End Get
End Property
Protected Overrides Sub OnFormClosed(ByVal e As System.Windows.Forms.FormClosedEventArgs)
'' Ensure that the one-and-only instance is now Nothing since it closed
MyBase.OnFormClosed(e)
MainWindow = Nothing
End Sub
Sub New()
'' Creating more than once instance of this form can't work, so complain
If MainWindow IsNot Nothing Then Throw New InvalidOperationException("Cannot create more than one instance of the main window")
InitializeComponent()
'' We need to keep track of this instance since the Instance property returns it
MainWindow = Me
End Sub
'' etc...
End Class
Now you can use MainForm.Instance anywhere in your classes, like MainForm.Instance.InvokeRequired. And you'll be reminded when you get it wrong with an exception.
I have a class in VB.NET that has a method (called CurrentValue) that returns a number. There is also an event that the class raises to indicate the number has changed. In the event handler on my form, I update a textbox using the exposed method.
Sort of like this:
Public WithEvents MyClass as New CustomClass
Private Sub MyClass_DataChanged() Handles MyClass.DataChanged
Text1.Text = MyClass.CurrentValue
End Sub
When I run this I get a "Debugger.Runtime.CrossThreadMessagingException" error. What could be doing this? I am instantiating MyClass in the same form that contains the textbox.
I can also set properties of the MyClass object without any trouble.
OK, here's what I did:
In the form I have this to handle the event:
Public Delegate Sub MyClassDataChangedDelegate()
Sub MyClassDataChanged() Handles MyClass.DataChanged
If Me.InvokeRequired Then
Me.Invoke(New MyClassDataChangedDelegate(AddressOf MyClassDataChanged))
Else
Me.Text1.Text = MyClass.CurrentValue
End If
End Sub
This seems to work. Thanks for the suggestion.