I'm working on an application to be able to monitor production information on a 3x3 (so 9 screen) video wall. One of the screen sets that I'm working on right now retrieves information and then formats for display on the screen. It takes about 2 seconds to retrieve and format this data (just a rough guess, not actually measured). Because it does 9 screen, one after the other, there is a very noticeable amount of time to switch to this screen set. The PC driving this video wall has 8 processing cores, so while one processor is chugging away doing all this work, there's plenty of processing power just sitting idle.
My first thought is that I need to use multi-threading. Unfortunately, I'm very new to this concept. I really have only used it one other time. I tried creating a BackgroundWorker and having the DoWork routine generate my UI. Unfortunately, it crashes the first time I try to create a UI element (Dim grLine as New Grid). I did manage to get around that by having a dummy DoWork routine and generating all my UI in the RunWorkerCompleted routine. This does allow my blank window to show up immediately, but none of the UI I'm generating shows up until it has all been rendered.
Here's a very cleaned up version of what I'm trying to do:
For i As Integer = 1 to 9
Dim win As New MyCustomWindow
win.DisplayScreen = i ' This function in MyCustomWindow sets the Bounds
win.MyShow({1, 2}) ' Sample args
Globals.VideoWall.Windows(i) = win
Next
The MyCustomWindow Class:
Class MyCustomWindow
Public Sub MyShow(a() as Integer)
Me.Show() ' Has a "Loading..." TextBlock
Dim bw as New ComponentModel.BackgroundWorker
AddHandler bw.DoWork, AddressOf Generate_UI_DoWork
AddHandler bw.RunWorkerCompleted, AddressOf Generate_UI_Complete
bw.RunWorkerAsync(a)
End Sub
Private Sub Generate_UI_DoWork((sender As Object, e As ComponentModel.DoWorkEventArgs)
' Pass our arguments to the Complete routine.
e.Result = e.Argument
End Sub
Private Sub Generate_OpsMarket_Complete(sender As Object, e As ComponentModel.RunWorkerCompletedEventArgs)
Dim IDs() as Integer
IDs = e.Result
Dim grLine As New Grid ' We crash here if this code is in DoWork instead of RunWorkerCompleted
For Each id As Integer In IDs
grLine.RowDefinitions.Add(New RowDefinition)
Dim txt as New TextBlock ' For a header
grLine.Children.Add(txt)
grLine.RowDefinitions.Add(New RowDefinition)
Dim MyCtrl as New MyCustomControl()
MyCustomControl.GetData(id)
grLine.Children.Add(MyCtrl.MyGrid)
txt.Text = MyCtrl.Header
Next
txLoading.Visibility = Visibility.Hidden
grRoot.Children.Add(grLine)
End Sub
End Class
I tried to leave enough detail in the code so hopefully it'll be evident what I'm trying to accomplish, but keeping it small enough to not be overwhelming.
Edited to add:
The bulk of the work happens in MyCustomControl.GetData(id) ... that Sub downloads the data from a web server (in JSON format), parses the JSON, then generates the rows (3) and columns (30 or 31, depending on the month) for the Grid and fills in the data it received from the web server.
Your current BackgroundWorker implementation give you no benefits, as you noticed by your self.
Your main problem is that your current code/logic tightly depend on UI controls. Which strict you with UI thread. Because creating/updating UI controls can be done only on UI thread - that's why you got Exception when trying create/update UI controls in BackgroundWorker.DoWork handler.
Suggest to separate logic which retrieve monitoring information in parallel and then you can create/update control on UI with already formatted data.
This is raw/pseudo example
Class DataService
Public Function GetData(ids As Integer()) As YourData
' Get data from web service
' Validate and Format it to YourData type or List(Of Yourdata)
Return data
End Function
End Class
Class MyCustomWindow
Public Sub MyShow(a() as Integer)
Me.Show() ' Has a "Loading..." TextBlock
Dim bw as New ComponentModel.BackgroundWorker
AddHandler bw.DoWork, AddressOf Generate_UI_DoWork
AddHandler bw.RunWorkerCompleted, AddressOf Generate_UI_Complete
bw.RunWorkerAsync(a)
End Sub
Private Sub Generate_UI_DoWork((sender As Object, e As ComponentModel.DoWorkEventArgs)
Dim service As New DataService()
Dim data = service.GetData(e.Argument)
e.Result = data
End Sub
Private Sub Generate_OpsMarket_Complete(sender As Object,
e As ComponentModel.RunWorkerCompletedEventArgs)
Dim data As Yourdata = DirectCast(e.Result, YourData)
'Update UI controls with already formatted data
End Sub
End Class
Update on Sub downloads the data from a web server
In this case you don't need multi-threading/parallel at all. Because you loading time is waiting time for response. In this case my advice will be using async/await approach, which will release UI thread(make it responsive) while you waiting for response from web-service.
Class DataService
Public Async Function GetDataAsync(ids As Integer()) As Task(Of YourData)
Using client As HttpClient = New HttpClient()
Dim response As HttpResponseMessage = Await client.GetAsync(yourUrl)
If response.IsSuccessStatusCode = True Then
Return Await response.Content.ReadAsAsync<YourData>()
End If
End Using
End Function
End Class
Then in the view you don't need BackgroundWorker
Class MyCustomWindow
Public Async Sub MyShow(a() as Integer) As Task
Me.Show() ' Has a "Loading..." TextBlock
Dim service As New DataService()
Dim data As YourData = Await service.GetDataAsync(a)
UpdateControlsWithData(data)
End Sub
Private Sub UpdateControlsWithData(data As YourData)
' Update controls with received data
End Sub
End Class
For what it's worth, here are a few examples which do 9 x 500ms of data operations, then simple UI operation.
The first example runs on a background thread but the main loop runs in sequence. The messagebox at the end shows that it takes around 4500 ms because of the 500 ms thread sleep is run sequentially. Notice how the DoWork method has nothing to do with the UI. It uses two threads: the UI thread and one background worker. Since it's not doing work on the UI, the form is responsive while the background worker is working.
Private bw_single As New BackgroundWorker()
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
AddHandler bw_single.DoWork, AddressOf bw_single_DoWork
AddHandler bw_single.RunWorkerCompleted, AddressOf bw_single_Complete
bw_single.RunWorkerAsync()
End Sub
Private Sub bw_single_DoWork(sender As Object, e As DoWorkEventArgs)
' runs on background thread
Dim data As New List(Of Integer)()
Dim sw As New Stopwatch
sw.Start()
For i As Integer = 1 To 9
' simulate downloading data, etc.
Threading.Thread.Sleep(500)
data.Add(i)
Next
sw.Stop()
e.Result = New Result(data, sw.ElapsedMilliseconds)
End Sub
Private Sub bw_single_Complete(sender As Object, e As RunWorkerCompletedEventArgs)
RemoveHandler bw_single.DoWork, AddressOf bw_single_DoWork
RemoveHandler bw_single.RunWorkerCompleted, AddressOf bw_single_Complete
' runs on UI thread
Dim res = CType(e.Result, Result)
Me.DataGridView1.DataSource = res.Data
MessageBox.Show(
String.Format("Performed on bw (single), took {0} ms, data: {1}",
res.Elapsed, String.Join(", ", res.Data)))
End Sub
(This is the class which holds the result of the background worker)
Private Class Result
Public Property Data As IEnumerable(Of Integer)
Public Property Elapsed As Long
Public Sub New(data As IEnumerable(Of Integer), elapsed As Long)
Me.Data = data
Me.Elapsed = elapsed
End Sub
End Class
The second example runs on a background thread but the main loop runs in parallel. The messagebox at the end shows that it takes around 1000 ms ... why? Because my machine like yours has 8 logical cores but we are sleeping 9 times. So at least one core is doing two sleeps and this will gate the entire operation. Again, there is one thread for the UI, one for the background worker, but for the parallel loop, the OS will allocate CPU time from the remaining cores to each additional thread. The UI is responsive and it takes a fraction of the time of the first example to do the same thing
Private bw_multi As New BackgroundWorker()
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
AddHandler bw_multi.DoWork, AddressOf bw_multi_DoWork
AddHandler bw_multi.RunWorkerCompleted, AddressOf bw_multi_Complete
bw_multi.RunWorkerAsync()
End Sub
Private Sub bw_multi_DoWork(sender As Object, e As DoWorkEventArgs)
' runs on background thread
Dim data As New ConcurrentBag(Of Integer)()
Dim sw As New Stopwatch
sw.Start()
Parallel.For(1, 9,
Sub(i)
data.Add(i)
Threading.Thread.Sleep(500)
End Sub)
sw.Stop()
e.Result = New Result(data, sw.ElapsedMilliseconds)
End Sub
Private Sub bw_multi_Complete(sender As Object, e As RunWorkerCompletedEventArgs)
RemoveHandler bw_multi.DoWork, AddressOf bw_multi_DoWork
RemoveHandler bw_multi.RunWorkerCompleted, AddressOf bw_multi_Complete
' runs on UI thread
Dim res = CType(e.Result, Result)
Me.DataGridView1.DataSource = res.Data
MessageBox.Show(
String.Format("Performed on bw (multi), took {0} ms, data: {1}",
res.Elapsed, String.Join(", ", res.Data)))
End Sub
Since the above two examples utilize background workers to do their work, they will not freeze the UI thread. The only code running on the UI is in the button click handlers and the RunWorkerCompleted handler.
Lastly, this example uses only a single UI thread. It will freeze the UI while it's running for 4500 seconds. Just so you know what to avoid...
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim data As New List(Of Integer)()
Dim sw As New Stopwatch
sw.Start()
For i As Integer = 1 To 9
' simulate downloading data, etc.
Threading.Thread.Sleep(500)
data.Add(i)
Next
sw.Stop()
Dim res = New Result(data, sw.ElapsedMilliseconds)
Me.DataGridView1.DataSource = res.Data
MessageBox.Show(
String.Format("Performed on bw (single), took {0} ms, data: {1}",
res.Elapsed, String.Join(", ", res.Data)))
End Sub
Summarily, you should figure out how to separate the data layer from the UI. See separation of concerns and the SO question, Why is good UI design so hard for some Developers?, and this one What UI design principles like “separation of concerns” can I use to convince developers that the UI needs fixing?
I've seen a few other posts about this but I seem to be confused since I've seen it done several ways and haven't gotten it correct any of the ways, so I thought I would ask specifically for my case so I can learn what I am doing wrong. After learning and switching to C# for most of my programming, VB.net seems so clunky in its syntax with a lot of things, especially lambda and "on-the-fly" functions.
I have a long running task for a football game I am working on where it generates players. Its an async method utilizing the Task.Factory.StartNew method.
Here is the pertinent code:
Private Sub CreateDraft_Click(sender As Object, e As RoutedEventArgs) Handles CreateDraft.Click
TimeIt(Sub() ReallyGenNewPlayers())
End Sub
'Uses a stopwatch to time how long it takes and sends to console.
Private Sub TimeIt(MyAction As Action)
Dim SW As New Stopwatch
SW.Start()
MyAction()
Console.WriteLine($"Total Time Generating Players: {SW.Elapsed} seconds")
SW.Stop()
End Sub
Private Async Sub GenNewPlayersASync()
Dim myvalue = 0
'Generate the Players on an Async Thread
Dim x As Integer
For i As Integer = 1 To NumPlayers
x = i 'avoids issue with using the iteration variable inside the delegate
CollegePlayers.GenDraftPlayers(i, MyDraft, DraftDT, DraftClass, PosCount)
'Prog_ValueChanged(DBNull.Value, New RoutedPropertyChangedEventArgs(Of Double))
'Calls a delegate to update the progress bar to avoid having the variable locked by the background thread
Dispatcher.Invoke(Sub()
worker.ReportProgress((x / NumPlayers) * 100)
End Sub)
Next i
End Sub
'Creates a task to run the player generation code and wait til its finished
Private Sub ReallyGenNewPlayers()
Dim mytask = Task.Factory.StartNew(Sub() GenNewPlayersASync())
Task.WaitAll(mytask)
End Sub
So here is what I would like to do:
I have a progressbar I created in XAML that has a Progress_Changed Event. This is what I have for it so far based on another post, but the issue is when I have to call the function inside GenNewPlayersAsync() where it wants a RoutedPropertyChangeEventArgs as a double which I'm not exactly sure what to do...I tried creating one using .New(old value, new value) but that didn't work either and threw an error.
Public Async Sub Prog_ValueChanged(sender As Object, e As RoutedPropertyChangedEventArgs(Of Double))
Dim progress = New Progress(Of Integer)(Function(percent)
Prog.Value = e.NewValue
Return Prog.Value
End Function)
Await Task.Run(Sub() DoProcessing(progress))
End Sub
Public Sub DoProcessing(progress As IProgress(Of Integer))
Dim i As Integer = 0
While i <> 100
Thread.Sleep(100)
' CPU-bound work
If progress IsNot Nothing Then
progress.Report(i)
End If
End While
End Sub
I would like for the progressbar to be bound to an INotifyChanged Property and update itself automatically when the value gets changed. None of it seems to be working. The UI is still unresponsive and when I set different parts to ASync, I start getting Exceptions where it appears certain parts of the generation algorithm aren't working as they are returning null...very confused with all of this, and I am sure the answer is probably pretty simple...
If you guys could give several examples of different ways to get this to work so I can learn different methods and maybe state the pros and cons of the method I would greatly appreciate it...
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})
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 using the below to restore a database in VB.NET.
This works but causes the interface to lockup if the user clicks anything.
Also, I cannot get the progress label to update incrementally, it's blank until the backup is complete then displays 100%
Sub DoRestore()
Dim svr As Server = New Server("Server\SQL2008")
Dim res As Restore = New Restore()
res.Devices.AddDevice("C:\MyDB.bak", DeviceType.File)
res.Database = "MyDB"
res.RelocateFiles.Add(New RelocateFile("MyDB_Data", "C:\MyDB.mdf"))
res.RelocateFiles.Add(New RelocateFile("MyDB_Log", "C:\MyDB.ldf"))
res.PercentCompleteNotification = 1
AddHandler res.PercentComplete, AddressOf ProgressEventHandler
res.SqlRestore(svr)
End Sub
Is this change correct?:
Private Sub ProgressEventHandler(ByVal sender As Object, ByVal e As PercentCompleteEventArgs)
UpdateProgressBar(e.Percent)
End Sub
Private Sub UpdateProgressBar(ByVal e As String)
ProgressBar.Value = e
Status.Text = e.ToString
End Sub
You need to use SqlRestoreAsync not SqlRestore to prevent it tying up your main thread.
Then to avoid the Cross Thread Operation error when updating the UI you can use the approach here. Where you create a method on the form that will update the UI elements and call that from your asynch handler using Invoke.