I've got the following situation,
Private Sub MyButton_Click(sender as Object, args as EventArgs) Handles MyButton.Click
Me.pleaseWaitFrm = New PleaseWaitForm()
' Fire up new thread to do some work in (AddressOf DoMyWork)
Me.pleaseWaitFrm.ShowDialog()
End Sub
Private Sub DoMyWork()
Dim log = Me.DoTheActualWork()
Me.pleaseWaitFrm.Close()
Using logFrm as New LogViewer(log)
logFrm.ShowDialog()
End Using
End Sub
If the DoTheActualWork() call exits fast enough, the Me.pleaseWaitFrm.Close() call is happening during the Me.pleaseWaitFrm.ShowDialog() call. The result, no surprise, is this exception:
An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll
Additional information: Value Close() cannot be called while doing CreateHandle().
Obviously this is the old "you cannot .Close() a WinForm while it's in the process of loading" problem. But what isn't obvious to me is how best to prevent that from happening in this case? How does one safely and reliably delay the .Close() until it is safe to do so in this situation?
Me.pleaseWaitFrm.Close()
That's an illegal call, you are not allowed to close a form from another thread. Not sure how you got away with it, that should raise an IllegalOperationException when you run with a debugger. Review your code and delete any assignment to the Control.CheckForIllegalCrossThreadCalls property.
This exception you're getting is a clear side-effect of this. You must use Control.Invoke() to get the dialog closed. This automatically solves your problem, the delegate target cannot execute until the dialog is loaded.
Leverage the BackgroundWorker class, it makes this easy. You can close the dialog in a RunWorkerCompleted event handler.
Why not set a "ShouldClose" flag which can be checked when it's safe to close the form - and close it if required?
With regards to a code example, I'd implement it slightly differently but let me know if this breaks any other requirements and we can modify it...
''in PleaseWaitForm:
Public Property ShouldClose as boolean = false
Private Sub frmSplash_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Close()
End Sub
''Your posted code
Private Sub MyButton_Click(sender as Object, args as EventArgs) Handles MyButton.Click
Me.pleaseWaitFrm = New PleaseWaitForm()
'' Fire up new thread to do some work in (AddressOf DoMyWork)
Me.pleaseWaitFrm.ShowDialog()
End Sub
Private Sub DoMyWork()
Dim log = Me.DoTheActualWork()
Me.pleaseWaitFrm.ShouldClose = True
If Me.pleaseWaitFrm.Created Then
Me.pleaseWaitFrm.Created.Close
End If
Using logFrm as New LogViewer(log)
logFrm.ShowDialog()
End Using
End Sub
In short, if we Can close the form, we do - otherwise, set a flag and the form will do it when it finishes loading.
I tested and didn't get any issues calling Me.Close inside the frmSplash.Load() but if you do encounter any problems, you can make it cast-iron by having a worked on frmSplash which checks the value rather than use the Load event
Edit: Spotted and fixed a bug
Related
I am trying to use a timer to scan my Xbox 360 controller. But I cannot directly update my UI like the code I wrote below.
I would get a exception when I try to run this code.
An exception of type 'System.InvalidOperationException' occurred in WindowsBase.dll but was not handled in user code
Additional information: The calling thread cannot access this object because a different thread owns it.
XButton is a radiobutton on the GUI that I want to toggle.
Imports Microsoft.Xna.Framework
Imports Microsoft.Xna.Framework.Input
Imports System.Timers
Imports System.Windows.Threading
Public Class XboxControllerStatus
Friend WithEvents Timer1 As Timer
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Elapsed
Dim currentState As GamePadState = GamePad.GetState(PlayerIndex.One)
If currentState.IsConnected Then
If currentState.Buttons.X.Pressed Then
XButton.IsChecked = True
Else
XButton.IsChecked = False
End If
End If
End Sub
End Class
This works for me, all the time
Control.Invoke(sub()
'Put code here
End Sub)
First you need to set up a delegate
Delegate Sub SetCheckBoxCallback(ByVal value As Boolean)
Friend Sub SetCheckBox(ByVal value As Boolean)
XButton.IsChecked = value
End Sub
after that all you need to do is call the following code from within your timer to invoke it:
Dim DesiredValue as Boolean = True
Me.Dispatcher.Invoke(New SetCheckboxCallback(AddressOf SetCheckbox), New
Object() {DesiredValue})
Branching off a previous question... Retrieving only PRINT command from SQL Server procedure in VB.NET
I was able to dump all the text from SQL Server's messages and use what I need but for some reason I am unable to update my textbox with the events.
Private Shared Sub OnInfoMessage(ByVal sender As Object, ByVal e As System.Data.SqlClient.SqlInfoMessageEventArgs)
Dim Counter As Integer
Counter = 1
For Each line In e.Message.Split(vbNewLine)
If (line.Contains("====")) Then
RestoreTool.txtTRNStatus.Text = "TRN #" & Counter & "Restored"
Using LogFile As IO.StreamWriter = New IO.StreamWriter("C:\SDBT\worklog.ft", True)
LogFile.WriteLine(line)
End Using
Counter += 1
End If
Next
Everything runs smoothly but the textbox (txtTRNStatus) does not update with anything and remains blank (Where it should be showing "TRN #1 Restored")
I am utilizing a Background Worker as well to call the procedure that actually performs the restoration of a database. That procedure is what contains the event handler for the SQLInfoMessages.
Dim SQL As SqlCommand
Dim DBConn As New SqlConnection(ConnectionString)
SQL = New SqlCommand(DBScript, DBConn)
AddHandler DBConn.InfoMessage, New SqlInfoMessageEventHandler(AddressOf OnInfoMessage)
Dim SQLResult As IAsyncResult = SQL.BeginExecuteNonQuery()
Try
Catch e As Exception
MessageBox.Show(e.Message)
End Try
SQL.EndExecuteNonQuery(SQLResult)
CompletedTask = True
DBConn.Close()
I have a feeling the only way I can get the text to update is through the addition of something in the DoWork() portion of the Backgroundworker but cannot figure out what exactly. Can the OnInfoMessages be called at will when an update is needed or is it only specific to where the Event Handler is?
As you can see in the image, It's during the actual "restoration" that the tool would normally report which transaction log has been restored based off of the SQL Message received but it remains blank...
Thank you once again!
EDIT: My progress update for my background worker is set up correctly, I just am having trouble calling events from the OnInfoMessage Sub as a progress update which is where gets the next line from SQL.
Make sure you use the backgroundworker properly. In the "doWork" there must not have any line of code that affect the UI(UserInterface) as this thread isn't the main thread of the application. If it does, it will either crash or do nothing.
So if you need to change the UI from the background worker you will need to tell the main thread to do so from the "DoWork" method. This can be achieved by hooking a callback to event "ProgressChanged" of your backgroundWorker object.
' This event handler updates the UI. '
Private Sub backgroundWorker1_ProgressChanged( _
ByVal sender As Object, ByVal e As ProgressChangedEventArgs) _
Handles backgroundWorker1.ProgressChanged
Me.txtTRNStatus.Text = e.UserState.ToString()//Update UI
End Sub
From the "DoWork" method, raise this event like shown below to tell main thread to update UI. Use the second parameter to pass whatever is needed by main thread to do so.
Private Sub backgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs)
' This method will run on a thread other than the UI thread. '
' Be sure not to manipulate any Windows Forms controls created'
' on the UI thread from this method.'
Dim SomeObject As [Object]
//some stuff
backgroundWorker.ReportProgress(1, SomeObject)
//some stuff
backgroundWorker.ReportProgress(2, SomeObject)
End Sub
See MSDN for more detail on backgroundworker usage.
Or you could just use "invoke" like #Mark suggested in the comment. This tell main thread execute a sub. As long as the UI update is done by the main thread you will be fine.
So my issue may sound familiar, I simply want to update a progress bar concurrently with the data that is being processed in my program.
I have two windows: StartupWindow and UpdateWindow.
The Application begins by creating the startup window, the user will push a button to open the UpdateWindow. The following is the code for the button:
Private Sub btnUpdateClick(sender As Object, e As RoutedEventArgs) Handles btnUpdate.Click
Dim updateWindow As New UpdateWindow
updateWindow.ShowDialog()
btnUpdate.IsEnabled = False
End Sub
With this code I got the error most other people do: "The calling thread cannot access this object because a different thread owns it."
Private Sub updateDevice()
Dim currPercent As Integer
currPercent = ((sentPackets / totalPacketsToWrite) * 100)
progressLabel.content = currPercent.ToString + "%"
pb.Maximum = totalPacketsToWrite
pb.Value = sentPackets
If sentPackets < totalPacketsToWrite Then
'....update....
Else
MsgBox("Device now has update stored on flash!")
'...close everything up
End If
End Sub
Here are the three things I have tried so far:
Use Invoke/Dispatcher/Delegate to try and seem to only be able to put the update in a different thread's queue? Can't seem to pause other the other threads to update the UI either...
Implement the BackgroundWorker Class and use report progress from it, this worked but I could only update the progress bar under bw.DoWork I make a lot of calls and have responses from external devices so it would be difficult to put all my code under one function.
I read somewhere that since this was the second window created (called from the original) I would have issues with it. So I took someone's solution and tried to create and entire new thread when the 'update' button was pressed ie.:
Something to note is that I added a 'cancel' button:
Private Sub buttonStart_Click(sender As Object, e As RoutedEventArgs) Handles btnStart.Click
btnStart.IsEnabled = False
btnStart.Visibility = Windows.Visibility.Hidden
btnCancel.IsEnabled = True
btnCancel.Visibility = Windows.Visibility.Visible
beginUpdate()
End Sub
Private Sub buttonCancel_Click(sender As Object, e As RoutedEventArgs) Handles btnCancel.Click
btnStart.IsEnabled = True
btnStart.Visibility = Windows.Visibility.Visible
btnCancel.IsEnabled = False
btnCancel.Visibility = Windows.Visibility.Hidden
'TODO MAKE IT CANCEL
End Sub
And every time I clicked the update/cancel button the progress bar would update. Every time I pressed the button it refreshed the progress bar to the current completion. I'm quite puzzled, I am able to update user interfaces if it is just one window... but if the user pushes a button to call a new window I cannot update anything in the second window. Any suggestions?
EDIT:
I ended up making global variables that updated in my long code. Than ran backgroundworker before I did anything else and it ran asynchronous to my process, updating the progress bar:
Private Sub bw_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
While finished = False
Threading.Thread.Sleep(50)
bw.ReportProgress(currPercent)
End While
End Sub
The start of my code was simple - like so:
Private Sub buttonStart_Click(sender As Object, e As RoutedEventArgs) Handles btnStart.Click
bw.RunWorkerAsync()
beginUpdate()
End Sub
First things first... get the ProgressBar working: For this part, please read my answer to the Progress Bar update from Background worker stalling question here on Stack Overflow. Now, let's assume that you've got the basic update of a ProgressBar working... next, you want to be able to cancel the work. It is a simple matter to update the DowWork method accordingly:
private void DoWork(object sender, DoWorkEventArgs e)
{
for (int i = 0; i <= 100; i++)
{
if (IsCancelled) break; // cancellation check
Thread.Sleep(100); // long running process
backgroundWorker.ReportProgress(i);
}
}
So all you need to do to cancel the long running process and the ProgressBar update is to set the IsCancelled property to true.
I'm trying to update a dependancy property in VB.Net 4.0 inside of an Async callback. I feel like I am doing this correctly but I'm still getting the "The calling thread cannot access this object because a different thread owns it." error. Does someone see a better way of using delegates in VB.Net 4.0?
Private WithEvents myObj as CallingObject
Private Delegate Sub MyErrorDel(ByVal strError as string)
Public Property ErrorMessage As String
Get
Return CStr(GetValue(ErrorMessageProperty))
End Get
Set(ByVal value As String)
SetValue(ErrorMessageProperty, value)
End Set
End Property
Private Sub MySub()
myObj.CallFuncAsync()
End Sub
Private Sub DisplayError(ByVal strError as String)
'Set Dependancy Property value Bound to UI Textbox
ErrorMessage = strError
End Sub
Private Sub myObj_CallFuncCompleted(Byval sender as Object, ByVal e as CallFuncEventArgs)
'Call delegate and pass in error string as argument
Dim delError as MyErrorDel
delError = New MyErrorDel(AddressOf DisplayError)
delError("An error occured")
Me.Dispatcher.Invoke(delError, System.Windows.Threading.DispatcherPriority.Normal, Nothing)
End Sub
Whenever ErrorMessage gets set inside of DisplayError an exception gets thrown, even though I am using the dispatcher to call DisplayError.
If anyone see any issues with the way I am trying to access Dependancy Properties from a async callback I would really appreciate the feedback.
Thanks for the help!
Oh and I'm pretty new at blogging about code issues. Any suggestions about how to better formulate this question would be welcome as well.
The problem might be that at the call to Me... you are already accessing an object owned by another thread, try to store a reference to the dispatcher beforehand or possibly use Application.Current.Dispatcher.
Since you didn't indicate the offending line, I suspect the problem here is that you're invokng your delegate in the line delError("An error occured") rather than waiting until you get to the dispatcher. Consider changing your CallFuncCompeted implementation to
Me.Dispatcher.Invoke(AddressOf DisplayError, "An error occureed")
Ok, now I can use 2 techniques to launch my threads: Dispatcher and BackgroundWorker.
Dispatcher:
' I launch the asynchronous process
Dim a As New Action(AddressOf operazioneLunga)
a.BeginInvoke(Nothing, Nothing)
' I update the GUI passing some parameters
Dim a As New Action(Of Integer, String)(AddressOf aggiorna_UI)
Me.Dispatcher.BeginInvoke(DispatcherPriority.Normal, a, 5, "pippo")
BackgroundWorker:
Private bw As BackgroundWorker = Nothing
Private Sub initial()
bw = New BackgroundWorker
AddHandler bw.DoWork, AddressOf longOp
AddHandler bw.RunWorkerCompleted, AddressOf endBGW
bw.RunWorkerAsync ()
End Sub
Private Sub longOp(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim l As List(Of miaClasse2) = <Long Operation ...>
e.Result = l
End Sub
Private Sub endBGW(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
Dim l As List(Of miaClasse2) = e.Result
Dim be As BindingExpression = BindingOperations.GetBindingExpression(mioDatagrid, DataGrid.ItemsSourceProperty)
Dim m As miaClasse1 = DirectCast(be.DataItem, miaClasse1)
m.GetData (l)
mioDatagrid.UpdateLayout()
mioDatagrid.ScrollIntoView (mioDatagrid.Items(0))
RemoveHandler bw.DoWork, AddressOf massiccia
RemoveHandler bw.RunWorkerCompleted, AddressOf fineBGW
bw.Dispose()
End Sub
I don't know what is better, but I think I'll use BackgroundWorker, because I suppose there are other argouments about Dispatcher I have to know and I don't feel safe.
Pileggi
My previous post:
Hi everyone!
My application is in WPF / Vb framework 3.5 SP1. I need to execute some methods on asynchronous threads. I know this way:
Private Delegate Sub dMassiccia()
Private Delegate Sub dAggiornaUI()
Private Sub iniziale()
Dim massicciaTemp As New dMassiccia(AddressOf massiccia)
massicciaTemp.BeginInvoke(Nothing, Nothing)
End Sub
Private Sub massiccia()
'long operations...
Me.Dispatcher.BeginInvoke(DispatcherPriority.Normal, _
New dAggiornaUI(AddressOf aggiornaUI))
End Sub
Private Sub aggiornaUI()
'update the UI...
End Sub
But in this way I have to declare a delegate for every mothod I want to launch on an asynchronous thread, and it's very uncomfortable. I have a lot of method to launch in this way. I know there are the anonymous delegates, but I don't know how to use them in this case.
Can you help me?
Pileggi
PS. Other information: in this moment I don't need to lookup the status of the process launched in the asynchronous thread. The long operations are some requests to a webservice that can take some seconds every time. There is no problem for the number of threads, because I limit the possibilities for the user to start new threads until one of them is finished. I need the asyncronous threads, among other reasons, because I don't wont to block the application, I want to replace the mouse cursor with a user-control, etc..
What is it that you're trying to do, that requires you to launch all of these threads? It looks like you're creating the secondary thread just to be able to do GUI updates.
First of all, if you have to create a lot of threads, then you run the risk of running out of available threads pretty quickly. I thought the max was only 64, but the documentation says 250 per process, and it's also settable via GetMaxThreads and SetMaxThreads. Regardless, you need to decide if using the ThreadPool threads (which is what's used when you use BeginInvoke/EndInvoke) is appropriate for you.
How long do your GUI updates take? Are they going to run the entire duration of your application? Can you use a regular thread instead? Look into using a BackgroundWorker for GUI updates if you just need to update status information periodically. In some cases, even DispatcherTimer might do the trick. It just depends on what you want to do.
You also don't show all of your code, but in what's posted, EndInvoke is not called. If you do this and end up throwing an exception, you won't be able to catch it and handle the error properly.