My current project requires a lot of forms. A lot of logic is the same so I want to create a BaseForm from which all Forms inherit.
I encounter a problem with UseWaitCursor and Cursor.Curent = Cursors.WaitCursor, it doesn't work if I load the data async (in a new Task).
This is the BaseForm:
Public MustInherit Class BaseForm
Inherits System.Windows.Forms.Form ' Normaly in BaseForm.Designer.vb put I put it here for symplicity
Protected Sub BeginLoadingData()
Application.UseWaitCursor = True
Cursor.Current = Cursors.WaitCursor
Application.DoEvents()
End Sub
Protected Sub EndLoadingData()
Application.UseWaitCursor = False
Cursor.Current = Cursors.Default
End Sub
End Class
And I use it like this:
Public Class MainForm
Inherits BaseForm ' Normaly in Mainform.Designer.vb put I put it here for symplicity
Public Sub New()
InitializeComponent()
LoadData()
End Sub
Private Sub LoadData()
BeginLoadingData() ' Working as long as I doesn't move the mouse
Task.Factory.StartNew(Sub()
' ... Long running task
Me.Invoke(Sub() EndLoadingData())
End Sub)
End Sub
End Class
If I run the loading synchronous, all works.
I wonder how I can force the cursor to stay WaitCursor.
Related
Need to call a sub that is coded written inside the block of form1 form an external worker thread. This is what I have written:
In Form1:
Public Delegate Sub UpdateControlDelegate(ByVal C As Label, ByVal txt As String)
Private Sub UpdateControl(ByVal C As Label, ByVal txt As String)
If C.InvokeRequired Then
C.Invoke(New UpdateControlDelegate(AddressOf UpdateControl), New Object() {C, txt})
Else
C.Text = txt
End If
End Sub
Public Sub DoStuff()
'we do some stuff then when it comnes time update a certain control:
Call UpdateControl(MyLabel, "My Text For The Label)
End Sub
In The workerThread that is located in a class:
Public Class MyClass
Public Sub UpdateData
Call Form1.DoStuff
End Sub
End Class
Does this look correct? The most simplest terms on what I am trying to achieve:
WorkerThread to call a Sub that is located in Class Form1
and that sub contains code that updates a couple controls in Form1.
After doing a little more research. I have figured it out. The initial code I have written is correct. The only thing missing is a reference to the form I need to update.
Here is the COMPLETE solution when needing to run a SUB from the UI that is called from the Worker Thread:
Public Class MyClass
'working thread is being within the subs of this class
Public MyForm1111 As Form1 '<------ The variable in this class that will reference to the form1 that we need
Public Sub MySubThatIsOnAWorkerThread
MyForm1111.DoStuff '<==== must call MyForm1111.DoStuff and NOT Form1.DoStuff
End Sub
End Class
The Sub Located In Form1:
Public Class Form1
Public Delegate Sub UpdateControlDelegate(ByVal C As Label, ByVal txt As String) 'Required Delegate
Private Sub UpdateControl(ByVal C As Label, ByVal txt As String) 'Sub to update controls
If C.InvokeRequired Then
C.Invoke(New UpdateControlDelegate(AddressOf UpdateControl), New Object() {C, txt})
Else
C.Text = txt
End If
End Sub
Public Sub DoStuff() 'the sub we need to call from the worker thread
'do some calculations and code
Call UpdateControl(MyLabel, "Some Text For Label")
End Sub
Private Sub Form1_Load()
MyClass.MyForm1111 = Me <==== Set the reference here in your Form1_Load
End Sub
End Class
If I have a class that implements INotifyPropertyChanged, and I have a property in that class that is bound to a label on a form, how do I avoid a Cross-threaded exception if I set the property value from a System.Timers.Timer.Elapsed event handler?
The following code demonstrates the exception.
Imports System.ComponentModel
Imports System.Timers
Public Class Form1
Private thisClass As New aClass
Private WithEvents tmr As New System.Timers.Timer()
Private lbl As System.Windows.Forms.Label
Public Sub New()
InitializeComponent()
'create the label and add it to the form
lbl = New Label
lbl.Text = "some text"
Me.Controls.Add(lbl)
'set the data binding and start a timer
lbl.DataBindings.Add("Text", thisClass, "X")
tmr.Interval = 1000
AddHandler tmr.Elapsed, AddressOf tmr_Elapsed
tmr.Start()
End Sub
Private Sub tmr_Elapsed(sender As Object, e As ElapsedEventArgs)
'change the property value when the timer elapses
thisClass.X = Guid.NewGuid.ToString
End Sub
End Class
Public Class aClass
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private _x As String = ""
Public Property X As String
Get
Return _x
End Get
Set(value As String)
_x = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("X"))
End Set
End Property
End Class
Alternative approach could be to use an asynchronous method to keep updating code on same thread.
Public Class MyForm
Private _viewmodel As MyViewModel
Private _intervalTask As Task
Private _canContinueIntervalRunning As Boolean
Public Sub New()
InitializeComponent()
_viewmodel = New MyViewModel()
CreateLabel() ' Create label and bind to viewmodel property
' Start interval without blocking this code execution
' Later we can use this saved task to make sure that task is complete
_canContinueIntervalRunning = True
_intervalTask = StartInterval()
End Sub
Private Async Function StartInterval() As Task
While _canContinueIntervalRunning
Await Task.Delay(1000)
_viewmodel.X = Guid.NewGuid().ToString()
End While
End Function
Private Async Sub FormClosing(sender as Object, e as FormClosingEventArgs) Handles MyForm.FormClosing
' Set "flag" to false and wait for task to complete
_canContinueIntervalRunning = False
Await _intervalTask
End Sub
End Class
With Await Task.Delay(1000) next line will be executed on same thread, which allows to update form controls without extra effort.
This is simple approach with boolean flag, another way of doing it would be to use cancellation token which you can pass to Task.Delay - then form don't need to wait for extra second, but can cancel Delay straight away.
I'm looking at a console app for vb.net. I'm trying to get a worker thread to raise an event to the main thread to display data on the screen (the word "HIT" everytime the worker thread completes a cycle). My code is below.
I'm not sure why but the main thread's Private Sub CounterClass_GivingUpdate() Handles _counter.AboutToDistributeNewupdate isn't executing.
Imports System.Threading
Module Module1
Private WithEvents _counter As CounterClass
Private trd As Thread
Sub Main()
While True
Dim s As String = Console.ReadLine()
Dim started As Boolean
Select Case s
Case "status"
WriteStatusToConsole("You typed status")
Case "startcounter"
If started = False Then
starttheThread()
started = True
WriteStatusToConsole("You Have Started The Timer")
Else
WriteStatusToConsole("YOU HAVE ALREADY STARTED THE TIMER!!!")
End If
End Select
End While
End Sub
Private Sub CounterClass_GivingUpdate() Handles _counter.AboutToDistributeNewupdate
WriteStatusToConsole("Hit")
End Sub
Private Sub starttheThread()
Dim c As New CounterClass
trd = New Thread(AddressOf c.startProcess)
trd.Start()
End Sub
Sub WriteStatusToConsole(ByVal stringToDisplay As String)
Console.WriteLine(stringToDisplay)
End Sub
End Module
Public Class CounterClass
Public Event AboutToDistributeNewupdate()
Public Sub sendStatusUpdateEvent(ByVal updatestatus As String)
RaiseEvent AboutToDistributeNewupdate()
End Sub
Public Sub startProcess()
Dim i As Int64
Do
Thread.Sleep(1000)
i = i + 1
sendStatusUpdateEvent(i.ToString)
Loop
End Sub
End Class
Your CounterClass_GivingUpdate() only handles the _counter variable's event (the variable that you do not use!). Every time you declare a new CounterClass it has its own instance of the event that it raises.
You know have two options:
Option 1
Subscribe to the event for each new CounterClass instance you create. Meaning you must use the AddHandler statement every time you create a new instance of your class:
Private Sub starttheThread()
Dim c As New CounterClass
AddHandler c.AboutToDistributeNewupdate, AddressOf CounterClass_GivingUpdate
trd = New Thread(AddressOf c.startProcess)
trd.Start()
End Sub
Option 2
Mark the event as Shared to make it available without needing to create an instance of the class. For this you must also change how you subscribe to the event, by subscribing to it in your method Main():
Sub Main()
AddHandler CounterClass.AboutToDistributeNewupdate, AddressOf CounterClass_GivingUpdate
...the rest of your code...
End Sub
Private Sub CounterClass_GivingUpdate() 'No "Handles"-statement here.
WriteStatusToConsole("Hit")
End Sub
Public Class CounterClass
Public Shared Event AboutToDistributeNewupdate() 'Added the "Shared" keyword.
...the rest of your code...
End Class
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.
I have two forms both with the same buttons on, and I want to have it so that if I click the button both buttons will do the same thing i.e. they are referencing each other on different forms. the way i found was:
Public Class Form2
Dim form1 As New form1
Private Sub Button2_Click
form1.backcolor=black
form2.backcolor=black
end sub
end class
then
Public Class Form1
Dim form2 As New form2
Private Sub Button1_Click
form1.backcolor=black
form2.backcolor=black
end sub
end class
only this doesn't work as there is an error:An unhandled exception of type 'System.StackOverflowException' occurred in System.Windows.Forms.dll as far as i can see there is no infinite loop or stack over flow.
any help would be greatly appreciated.
You have an infinite loop, because each time one of the forms is instantiated, it is instantiating the other. Creating a Form1 will create a Form2, then Form2 immediately creates another Form1 and so on and so on...
Change your code to this:
Public Class Form2
Private Sub Button2_Click
Dim form1 As New Form1
form1.backcolor=black
form2.backcolor=black
End sub
End class
Public Class Form1
Private Sub Button1_Click
form1.backcolor=black
Dim form2 As New Form2
form2.backcolor=black
End sub
End class
Now it will only create the other class instances when you click a button.
Like Karl Anderson said, there is a infinite loop in your code. His solution will create a new form every time you click the button. If you don't want this behavior, I think that the best approach is to use the mediator pattern. And it will be much more easy if you want to add new actions and new forms.
The code will look something like this:
Public Class Mediator
Private forms As New List(Of BaseForm)
Public Sub RegisterForm(form As BaseForm)
forms.Add(form)
End Sub
Public Sub ChangeAllFormsBackColorToBlack()
For Each form In forms
form.ChangeBackColorToBlack()
Next
End Sub
End Class
Public Class BaseForm
Private med As Mediator
Public Sub New(med As Mediator)
Me.med = med
Me.med.RegisterForm(Me)
End Sub
Public Sub ChangeBackColorToBlack()
backcolor = black
End Sub
Public Sub OnButtonClick()
Me.med.ChangeAllFormsBackColorToBlack()
End Sub
End Class
Public Class Form2
Inherits BaseForm
Public Sub New(med As Mediator)
MyBase.New(med)
End Sub
Private Sub Button2_Click()
Me.OnButtonClick()
End Sub
End Class
Public Class Form1
Inherits BaseForm
Public Sub New(med As Mediator)
MyBase.New(med)
End Sub
Private Sub Button1_Click()
Me.OnButtonClick()
End Sub
End Class
Module MediatorDemo
Sub Main()
Dim med As New Mediator
Dim f1 As New Form1(med)
Dim f2 As New Form2(med)
f1.OnButtonClick()
End Sub
End Module