I need to create multiple threads when a button is clicked and i've done that with this:
Dim myThread As New Threading.Thread(AddressOf getFile)
myThread.IsBackground = True
myThread.Start()
but i need to update a picture box with the downloaded file, buy if i set an event in the function getFile and raise it to notify that the files was downloaded and then update the picturebox.
Use an AsyncResult, and either check it periodically for completion, or provide a delegate to be called when the thread has completed its work.
A complete example in VB can be found here.
You need to make use of MethodInvoker deligate.
Public Sub GetFile()
If Me.InvokeRequired Then
Me.Invoke(New MethodInvoker(GetFile))
End If
End Sub
Now you can handle any event in your specified class.
You can achive that using the Asyncallback, ...
Dim sinctotal As New Del_sinc(AddressOf sincronizar)
Dim ar As IAsyncResult = sinctotal.BeginInvoke(_funcion, type, New AsyncCallback(AddressOf SincEnd), cookieobj)
The cookieobj is this
Class Cookie
Public id As String
Public AsyncDelegate As [Delegate]
Sub New(ByVal id As String, ByVal asyncDelegate As [Delegate])
Me.id = id
Me.AsyncDelegate = asyncDelegate
End Sub
End Class
When the delegate finish it will call the funcion Sincend (in this example), then you could use a event to update your picture.
Hope this helps!
Related
I have an application whose main window upon click of a button gives users an option to load a list of files in the cloud.
Private Sub ImportCloudContent()
Dim cloudForm As Form_CloudImport
cloudForm = New Form_CloudImport()
cloudForm.Show()
cloudForm.populateDataGrid()
AddHandler cloudForm._DownloadComplete, New EventHandler(AddressOf OpenProject)
cloudForm.DownloadNotifier(FullPathOfContent)
End Sub
Ideally I should be able to get the value of the FullPathOfContent variable and pass it onto Open Project, but I am not sure how to go about it.
In the new Window users can click and download the file they want. Below is the section of code that handles the download in the Form_CloudImport class :
Private Async Sub Btn_download_Click(sender As Object, e As EventArgs) Handles Btn_download.Click
Dim fileNameRows As DataGridViewSelectedRowCollection = datagridview_cloudContent.SelectedRows
Dim fileName As String
Dim fileType As String = Cloud.CONTENT
Dim FullPathOfContent As String
For Each fileNameRow As DataGridViewRow In fileNameRows
fileName = fileNameRow.Cells(0).Value.ToString() & ".zip"
Try
FullPathOfContent = CloudToCCT(fileName, fileType)
Catch ex As Exception
CSMessageBox.ShowError("Content Import failed : ", ex)
End Try
Next
Me.Close()
DownloadNotifier(FullPathOfContent)
End Sub
Once the download is complete, the main window needs to call some of its methods. I am new to VB and have created a custom event to facilitate this(again in the Form_CloudImport class)
Public Event _DownloadComplete(e As String)
Public Sub DownloadNotifier(FullPathOfContent As String)
RaiseEvent _DownloadComplete(FullPathOfContent)
End Sub
According to what have read, once the download method is complete, it will fire the DownloadNotifier method, which will raise the _DownloadComplete event and the MainWindow should trigger the following events.
However, I receive the below errors in the MainWindow part of the code :
Value of type 'MainWindow.EventHandler' cannot be converted to 'Form_CloudImport._DownloadCompleteEventHandler'
and
'FullPathOfContent' is not declared. It may be inaccessible due to its protection level.
This question seems to be very long but any help would be appreciated. Thank you in advance!
First things first, you should create a type and event with proper names and signature and raise it properly.
Public Class CloudImportForm
Public Event DownloadComplete As EventHandler(Of DownloadCompleteEventArgs)
Protected Overridable Sub OnDownloadComplete(e As DownloadCompleteEventArgs)
RaiseEvent DownloadComplete(Me, e)
End Sub
'...
End Class
Public Class DownloadCompleteEventArgs
Inherits EventArgs
Public Sub New(contentPath As String)
Me.ContentPath = contentPath
End Sub
Public ReadOnly Property ContentPath As String
End Class
In that form, you would have code that performed a download and then raised that event.
'...
Dim contentPath = GetContentPath()
'Perform download here.
'Raise event.
OnDownloadComplete(New DownloadCompleteEventArgs(contentPath))
In your main form you would create and configure the download form, which includes handling the event, and then display it.
Dim cloudForm As New CloudImportForm
AddHandler cloudForm.DownloadComplete, AddressOf CloudImportForm_DownloadComplete
cloudForm.PopulateDataGrid()
cloudForm.Show()
The method you specify as the event handler should have the appropriate signature and it should retrieve the content path from the e parameter.
Private Sub CloudImportForm_DownloadComplete(sender As Object, e As DownloadCompleteEventArgs)
Dim contentPath = e.ContentPath
'Use contentPath here.
End Sub
I am writing a VB form application that redirects the standard output stream of a process and uses it in a UI.
I am having trouble calling methods with parameters that update controls on the form from the OutputHandler sub.
I can call a method without parameters like so
Me.Invoke(New MyDelSub(AddressOf ServerStarted))
Which works fine.
And a bit of googling told me that to call a method with parameters I should do this:
Dim del As JoinDelegate = AddressOf PlayerJoins
del.Invoke(username)
With this delegate and method pair:
Private Delegate Sub JoinDelegate(ByVal username As String)
Private Sub PlayerJoins(ByVal username As String)
PlayersBox.Items.Add(username)
'Do other stuff
End Sub
But this produces an IllegalOperationException the first time the method tries to access a control.
1) Supposing you have a method like this:
Public Sub DoSomething(value1 As String, value2 As String)
MessageBox.Show(String.Format("{0} {1}", value1, value2))
End Sub
You can call it using invoke this way:
Me.Invoke(Sub() DoSomething("Hello", "World!"))
2) If you want to make thread safe call to a control you can write the method this way:
Public Sub AddItemToListBox1(item As String)
If (ListBox1.InvokeRequired) Then
ListBox1.Invoke(Sub() AddItemToListBox1(item))
Else
ListBox1.Items.Add(item)
End If
End Sub
Then it's enough to call it in a the UI thread or in another thread the same way simply:
AddItemToListBox1("some item")
The call would be thread safe.
E.g.
Private Sub SetControlText(control As Control, text As String)
If control.InvokeRequired Then
control.Invoke(New Func(Of Control, String)(AddressOf SetControlText), control, text)
Else
control.Text = text
End If
End Sub
Call that method from any thread.
I'm having some trouble getting cross-thread communication/field-updating working properly in my VB.NET 2010 program. I'm trying to update a field on my main form whenever a thread that I've started throws an event. Here's a simplified version of my code:
My main form:
Public Class Main
' stuff
' Eventually, startProcessing gets called:
Private Sub startProcessing()
Dim processingClass = New MyProcessingClass("whatever")
AddHandler processingClass.processStatusUpdate, AddressOf handleProcessStatusUpdate
Dim processingThread = New Thread(AddressOf processingClass.process)
processingThread.Start()
End Sub
Private Sub handleProcessStatusUpdate(statusUpdate As String)
txtMainFormTextBox.Text = statusUpdate ' InvalidOperationException
' "Cross-threaded operation not valid: Control 'txtMainFormTextBox' accessed from a thread other than the thread it was created on"
End Sub
End Class
The class which raises the event:
Public Class MyProcessingClass
Private whatever As String
Public Event processStatusUpdate(status As String)
Public Sub New(inWhatever As String)
whatever = inWhatever
End Sub
Public Sub process()
' do some stuff
RaiseEvent processStatusUpdate(whatever)
End Sub
End Class
As you can see, the handler in my main class doesn't have access to the TextBox I need since it was triggered by a different thread (I think). I've tried a number of other approaches to get this working, including:
Moving the event handler to MyProcessingClass, and passing txtMainFormTextBox by reference (ByRef) to the class.
Having the actual thread start inside of MyProcessingClass instead of Main.
None of these have worked. Clearly there's a concept that I'm missing here. What's the best way to get this done? Thanks!
You need to update the textbox on the UI thread by calling BeginInvoke.
You should use the BackgroundWorker component, which does all of this for you.
Simply handle the DoWork and ProgressChanged events.
I'm looking to pass two or more parameters to a thread in VB 2008.
The following method (modified) works fine without parameters, and my status bar gets updated very cool-y.
But I can't seem to make it work with one, two or more parameters.
This is the pseudo code of what I'm thinking should happen when the button is pressed:
Private Sub Btn_Click()
Dim evaluator As New Thread(AddressOf Me.testthread(goodList, 1))
evaluator.Start()
Exit Sub
This is the testthread method:
Private Sub testthread(ByRef goodList As List(Of OneItem), ByVal coolvalue As Integer)
StatusProgressBar.Maximum = 100000
While (coolvalue < 100000)
coolvalue = coolvalue + 1
StatusProgressBar.Value = coolvalue
lblPercent.Text = coolvalue & "%"
Me.StatusProgressBar.Refresh()
End While
End Sub
First of all: AddressOf just gets the delegate to a function - you cannot specify anything else (i.e. capture any variables).
Now, you can start up a thread in two possible ways.
Pass an Action in the constructor and just Start() the thread.
Pass a ParameterizedThreadStart and forward one extra object argument to the method pointed to when calling .Start(parameter)
I consider the latter option an anachronism from pre-generic, pre-lambda times - which have ended at the latest with VB10.
You could use that crude method and create a list or structure which you pass to your threading code as this single object parameter, but since we now have closures, you can just create the thread on an anonymous Sub that knows all necessary variables by itself (which is work performed for you by the compiler).
Soo ...
Dim Evaluator = New Thread(Sub() Me.TestThread(goodList, 1))
It's really just that ;)
Something like this (I'm not a VB programmer)
Public Class MyParameters
public Name As String
public Number As Integer
End Class
newThread as thread = new Thread( AddressOf DoWork)
Dim parameters As New MyParameters
parameters.Name = "Arne"
newThread.Start(parameters);
public shared sub DoWork(byval data as object)
{
dim parameters = CType(data, Parameters)
}
Dim evaluator As New Thread(Sub() Me.testthread(goodList, 1))
With evaluator
.IsBackground = True ' not necessary...
.Start()
End With
Well, the straightforward method is to create an appropriate class/structure which holds all your parameter values and pass that to the thread.
Another solution in VB10 is to use the fact that lambdas create a closure, which basically means the compiler doing the above automatically for you:
Dim evaluator As New Thread(Sub()
testthread(goodList, 1)
End Sub)
In addition to what Dario stated about the Delegates you could execute a delegate with several parameters:
Predefine your delegate:
Private Delegate Sub TestThreadDelegate(ByRef goodList As List(Of String), ByVal coolvalue As Integer)
Get a handle to the delegate, create parameters in an array, DynamicInvoke on the Delegate:
Dim tester As TestThreadDelegate = AddressOf Me.testthread
Dim params(1) As Object
params(0) = New List(Of String)
params(1) = 0
tester.DynamicInvoke(params)
Just create a class or structure that has two members, one List(Of OneItem) and the other Integer and send in an instance of that class.
Edit: Sorry, missed that you had problems with one parameter as well. Just look at Thread Constructor (ParameterizedThreadStart) and that page includes a simple sample.
Pass multiple parameter for VB.NET 3.5
Public Class MyWork
Public Structure thread_Data
Dim TCPIPAddr As String
Dim TCPIPPort As Integer
End Structure
Dim STthread_Data As thread_Data
STthread_Data.TCPIPAddr = "192.168.2.2"
STthread_Data.TCPIPPort = 80
Dim multiThread As Thread = New Thread(AddressOf testthread)
multiThread.SetApartmentState(ApartmentState.MTA)
multiThread.Start(STthread_Data)
Private Function testthread(ByVal STthread_Data As thread_Data)
Dim IPaddr as string = STthread_Data.TCPIPAddr
Dim IPport as integer = STthread_Data.TCPIPPort
'Your work'
End Function
End Class
I think this will help you...
Creating Threads and Passing Data at Start Time!
Imports System.Threading
' The ThreadWithState class contains the information needed for
' a task, and the method that executes the task.
Public Class ThreadWithState
' State information used in the task.
Private boilerplate As String
Private value As Integer
' The constructor obtains the state information.
Public Sub New(text As String, number As Integer)
boilerplate = text
value = number
End Sub
' The thread procedure performs the task, such as formatting
' and printing a document.
Public Sub ThreadProc()
Console.WriteLine(boilerplate, value)
End Sub
End Class
' Entry point for the example.
'
Public Class Example
Public Shared Sub Main()
' Supply the state information required by the task.
Dim tws As New ThreadWithState( _
"This report displays the number {0}.", 42)
' Create a thread to execute the task, and then
' start the thread.
Dim t As New Thread(New ThreadStart(AddressOf tws.ThreadProc))
t.Start()
Console.WriteLine("Main thread does some work, then waits.")
t.Join()
Console.WriteLine( _
"Independent task has completed main thread ends.")
End Sub
End Class
' The example displays the following output:
' Main thread does some work, then waits.
' This report displays the number 42.
' Independent task has completed; main thread ends.
With VB 14, you can do the following with Tuples:
Shared Sub _runner(data as (goodList As List(Of OneItem), coolvalue As Integer))
Console.WriteLine($"goodList: {data.goodList}")
Console.WriteLine($"coolvalue: {data.coolvalue}")
' do stuff...
End Sub
Dim thr As New Thread(AddressOf _runner)
thr.Start((myGoodList, cval))
In my application, I have a MainWindow with a ToolStripProgressBar and a ToolStripStatusLabel.
This properties:
Property ProgressBarPercantage() As Integer Implements BCSXPSearchTool.Presenter.IMainView.ProgressPercentage
Get
Return Me._progressbarpercentage
End Get
Set(ByVal value As Integer)
Me._progressbarpercentage = value
Me.StatusStripCurrentProgressBar.Value = Me._progressbarpercentage
End Set
End Property
Private _progressbarpercentage As Integer = 0
Property ProgressStatusText() As String Implements BCSXPSearchTool.Presenter.IMainView.ProgressStatusText
Get
Return Me._progressstatustext
End Get
Set(ByVal value As String)
Me._progressstatustext = value
Me.StatusStripCurrentState.Text = Me._progressstatustext
End Set
End Property
Private _progressstatustext As String = "Ready"
In the MainWindowPresenter I start a new BackgroundWorker which should read from a database.
Public Sub Search()
Dim bw As New BackgroundWorker
bw.WorkerReportsProgress = True
bw.WorkerSupportsCancellation = True
AddHandler bw.DoWork, AddressOf runproc
If bw.IsBusy = False Then
bw.RunWorkerAsync()
End If
End Sub
Public Sub runproc()
Dim statusToSub As delegateStatusTo = AddressOf statusTo
Dim percToSub As delegatePercTo = AddressOf percTo
statusToSub.Invoke("Test")
'percToSub.Invoke(50)
End Sub
Public Sub percTo(ByVal value As Integer)
_view.ProgressPercentage = value
End Sub
Public Sub statusTo(ByVal value As String)
_view.ProgressStatusText = value
End Sub
Delegate Sub delegateStatusTo(ByVal value As String)
Delegate Sub delegatePercTo(ByVal value As Integer)
The code above is working. But if I change the sub runproc() to:
Public Sub runproc()
Dim statusToSub As delegateStatusTo = AddressOf statusTo
Dim percToSub As delegatePercTo = AddressOf percTo
' statusToSub.Invoke("Test")
percToSub.Invoke(50)
End Sub
It doesn't work. I get an exception:
InvalidOperationException
I got the text in english and can't translate it to english very well but I think something like:
The access to the control, created by another thread from another thread is not allowed.
I'm using Visual Studio 2008 Express + VB 2.0.
Thank you!
This is due to cross-thread UI access which is disallowed (but for every UI access, so your other code shouldn’t work either!). The easiest solution is to use BeginInvoke when required:
Public Sub statusTo(ByVal value As String)
If InvokeRequired Then
BeginInvoke(New Action(Of String)(AddressOf statusTo))
Return
End If
_view.ProgressStatusText = value
End Sub
Furthermore, #vulkanino’s comment is spot-on: your calls should be direct method calls, not delegate invocations.
Dim statusToSub As **new** delegateStatusTo(AddressOf WriteToDebug)
statusToSub.Invoke("Test")
Dim percToSub As **new** delegatePercTo (AddressOf percTo)
percToSub.Invoke(50)
It looks like you are attempting to access UI controls from the DoWork event handler. Remember, that event handler is running on a worker thread. You are not allowed to touch any UI control from a thread other than the one that created it. There is a ProgressChanged event that will be marshaled onto the UI thread automatically upon calling ReportProgress. You safely update the UI from this event.