I have a program that is doing one task.
For Example i have one list box containing some links.
And on the other hand my program is opening them one by one but i want it to be done faster
i have used for-each loop for that purpose.
All what i want to do is i wanna give every 2 or 3 link to a different thread or if there is any other solution to make it Faster Kindly tell me.
This is a small piece of code from my program.
For value As Integer = 1 To TextBox1.Text
If (value = TextBox1.Text) Then
Exit For
End If
Dim page As String = "-p-" & value
Extractor.ScrapLinks(txturl.Text + page, lstbox)
lbllinks.Text = lstbox.Items.Count
Next
I don't know what Extractor.ScrapLinks actually do, but it seems that you need to access UI thread and you cannot create multiple UI threads so eventually you will process them sequentially
What you can do to improve the solution is to read the data you want from the UI controls and then process that data on a separate thread, after completion you can fill the results into the UI by invoking some method on the UI thread as shown below
Delegate Sub PerformOperationDel(value As Integer)
Sub PerformOperation(value As Integer)
Dim page As String = "-p-" & value
Extractor.ScrapLinks(txturl.Text + page, lstbox)
lbllinks.Text = lstbox.Items.Count
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
For value As Integer = 1 To CInt(TextBox1.Text) - 1
lstbox.BeginInvoke(New PerformOperationDel(AddressOf PerformOperation))
Next
End Sub
You can use backgroundworkers but notice that you cannot access UI controls in the DoWork but you can access them on work completed (Refer to: Background worker proper way to access UI)
Best of luck
Related
I have a form with combo boxes (cmbPort#) to select up to 8 serial ports. I want to first clear the item list for each, populate them with currently available system ports, and then add the option "Off" to each list. Finally, to set each combo box according to defaults saved in string spName(). I created a GroupBox (gBox1) and dragged each cmbPort onto it but I'm not sure how to reference the controls on it. I'm using VB 2015.
Can you help with VB.NET code to use loops ("For Each" or similar) to do this more efficiently?
Private Sub frmProp_Load(sender As Object, e As EventArgs) Handles MyBase.Load
cmbPort1.Items.Clear()
...
cmbPort8.Items.Clear()
For Each sp As String In My.Computer.Ports.SerialPortNames
cmbPort1.Items.Add(sp)
...
cmbPort8.Items.Add(sp)
Next
cmbPort1.Items.Add("Off")
...
cmbPort8.Items.Add("Off")
cmbPort1.Text = spName(1)
...
cmbPort8.Text = spName(8)
End Sub
Loops are an incredibly useful tool to master. I pitched here some code so you can get the idea, but I was working out of IDE so you might have to apply some fixes to this code to make it work as you want it to.
The main idea is that you shouldn't have to write a line more than once. If you multiply the same operation on several lines of code, you create potential problems for the future. Loops and subs are really helpful to prevent this kind of issues.
Private Sub frmProp_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'This is for later
Dim cmbIndex As Integer = 1
'You basically do the same operations for every Combobox in your list, son only one loop needed
For Each cmbPort As ComboBox In {cmbPort1, cmbPort2, cmbPort3 [...] cmbPort8} 'this is a way to declare an array
'Clear
cmbPort.Items.Clear()
'Add SerialPortNames
For Each sp As String In My.Computer.Ports.SerialPortNames
cmbPort.Items.Add(sp)
Next
'Add "Off"
cmbPort.Items.Add("Off")
'This last one is a little bit trickier because you want to match numbers
'This is the place where you get errors when something doesn't go as planned
'If you need to keep it inside the loop here's a way to achieve that, but honestly I would't do that
'Instead I would suggest that you take this part out of the loop and do it manually
If spName(cmbIndex) IsNot Nothing Then cmbPort.Text = spName(cmbIndex)
cmbIndex += 1
Next
End Sub
You shouldn't consider efficiency into this equation, as this operation will not be called all the time, only on load. I mean: you should always do things in the best way you can, but optimization is sometimes the enemy of good, readable code.
i'm trying to popup a msgbox everytime the current time is equal to a field in a table in the database i'm using the following code:
For i As Integer = 0 To contentTable.Rows.Count() - 1
UpdateListBoxRec2("Sending content " & i + 1 & " to :")
For j As Integer = 0 To subTable.Rows.Count() - 1
While send = False
If contentTable.Rows(i).Item(1) = DateTime.Now.ToString("hh:mm") Then
UpdateListBoxRec2(subTable.Rows(j).Item(0))
MsgBox(contentTable.Rows(i).Item(0))
send = True
End If
End While
'send = False
Next
Next
this method works but when the debugger is in the while loop ( means when the current time is not yet equal to the time i have in my db table ) i can't use any tool of my windows app untill the debugger gets out of the while loop so i'm searching for a similar method to popup my msgbox in the same condition and to be able to use my tools in the app all the time
please note that i'm using vb.net
any help please :)
You should never sit in an endless loop, like that, on the UI thread. As long as the UI thread is busy, it will be blocked from processing any incoming window messages (e.g. key strokes, mouse clicks). You could sit in a loop like that if you were on a separate thread, but that would be silly. The more sane solution would be to use a timer. For instance, if you drop a Timer component onto your form in the designer, and set it's Interval property to 5000 (five seconds), you can then add the following code:
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
For i ...
For j ...
If contentTable.Rows(i).Item(1) = DateTime.Now.ToString("hh:mm") Then
UpdateListBoxRec2(subTable.Rows(j).Item(0))
MessageBox.Show(contentTable.Rows(i).Item(0))
End If
Next
Next
End Sub
Now it will just run that code once every five seconds rather than continuously checking the current time and thereby hogging the UI thread.
I am trying to read/use the output from a python program in my vb.net project so far I'm not getting any results. What I'd like to see is the python program run (just by itself first) and all of the output get redirected into a textbox.
I've looked at some other posts about this, but I'm either missing something or not understanding something, as all I'm getting is blank output.
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim PythonPath = "C:\Python27\"
Dim strPath As String = Application.StartupPath
MessageBox.Show(PythonPath & "python.exe """ & strPath & "\Resources\import_logs.py"" ")
Dim start_info As New ProcessStartInfo(TextBox1.Text)
' Make the process and set its start information.
Dim process As New Process()
process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden
process.StartInfo.FileName = PythonPath & "\python.exe"
process.StartInfo.Arguments = """" & strPath & "\resources\import_logs.py"""""
process.StartInfo.UseShellExecute = False
process.StartInfo.CreateNoWindow = True
process.StartInfo.RedirectStandardOutput = True
'process.StartInfo.RedirectStandardError = True
AddHandler process.OutputDataReceived, AddressOf proccess_OutputDataReceived
process.Start()
process.BeginOutputReadLine()
End Sub
Public Sub proccess_OutputDataReceived(ByVal sender As Object, ByVal e As DataReceivedEventArgs)
On Error Resume Next
' output will be in string e.Data
' modify TextBox.Text here
'Server_Logs.Text = e.Data ` Does not display anything in textbox
MsgBox(e.Data) 'It works but I want output in text box field
End Sub
End Class
Eventually I'm going to pass arguments to the python script and I'd like to get feedback that I can then use (insert error into a database, email when it's done, etc), so I'd like it to capture the process while running and not just a data dump at the end.
Any help would be much appreciated.
First things first—it's no wonder you aren't sure what's wrong with your code, you're silencing all errors that could possibly help you to diagnose it. That's the only purpose of On Error Resume Next in VB.NET. That unstructured error handling was included only for backwards compatibility with the pre-.NET versions of VB and it's time to forget that it ever existed. You certainly don't want to use it in code. (I would say "in code that you're debugging", but all code is a potential candidate for debugging and ignoring errors is just dumb.)
Anyway, on to the specific problem. We know that the call to MsgBox works, but it doesn't work right when you start interacting with controls on your form. So something is falling apart there.
It turns out that the OutputDataReceived event is raised on an entirely different thread, a different one than was used to create the process and a different one than is running your application's UI. It actually just retrieves a thread from the system thread pool.
And that's where the problem lies: you cannot manipulate UI objects on a thread other than the one that created those objects (at least not without jumping through some hoops), which is precisely what your code tries to do here. In fact, you're probably swallowing an exception that would have rather obtusely informed you of this situation.
The simple fix is to set the SynchronizingObject property of the Process class to one of your UI components (like the form, or the specific control you want to output to). This forces all event handlers to execute on the same thread that created that component. At that point, your code should work fine, because you're not trying to do any cross-thread UI access. (Message boxes are not vulnerable to this because any thread can display a message box. You're not trying to access an existing UI object that is bound to another thread.)
Alternatively, you could handle the marshalling yourself in the event handler method through the use of delegates and the BeginInvoke method, but this seems like unnecessary work to me.
With the intention of creating a program to interface with a serial port device, I recently started learning vb.net. To keep the structure neat the vb code has been split into two places; the first is the code behind for initialising, clicking buttons etc., whilst the second is for managing the comm port. Respectively, these are named 'MainWindow.xaml.vb' and 'ComPortManager.vb'.
In 'comPortManager.vb':
Dim RXArray(2047) As Char ' Array to hold received characters
Dim RXCnt As Integer ' Received character count
Private Sub comPort_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs) Handles comPort.DataReceived
Do
RXCnt = 0
Do
'Populates the array, RXArray and counts the number of characters, RXCnt
Loop Until (comPort.BytesToRead = 0) 'Keeps reading the buffer until it is empty
'Code for posting to the richTextBox
Loop Until (comPort.BytesToRead = 0) 'If the buffer has been written to in the meantime, repeat
End Sub
The 'MainWindow.xaml' contains a ribbon (Microsoft's October 2010 release) with controls for settings, opening, closing and sending (keeping it all separate and simple for now), with the rest of the window being a richTextBox entitled 'RichTextBox1'.
The search for a way to post the contents of RXArray to RichTextBox1 brought up many suggestions based around Invoke or BeginInvoke. Indeed, working examples have been run successfully but all the code associated with Invoke has been in one file, the code behind. (Correct me if I'm wrong, but this sounds fine for small programs but could get bloated with medium to larger programs, hence me wanting to find a better solution)
The code closest to running (I believe) is as follows:
'In comPort_DataReceived... after populating the array
If RichTextBox1.InvokeRequired Then
RichTextBox1.Invoke(New MethodInvoker(AddressOf Display))
End If
'and back in the main code
Public Delegate Sub MethodInvoker()
Private Sub Display()
RichTextBox1.AppendText(New String(RXArray, 0, RXCnt))
End Sub
This has a few problems and I'm not sure in what direction to go at this stage. RichTextBox1 is in a different thread hence not recognised; InvokeRequired is not a member of System.Windows.Controls.RichTextBox, likewise with Invoke; and finally, in examples, the delegate entitled MethodInvoker was never stated as above.
Any help on this topic is most appreciated. In these few weeks, Invoke, BeginInvoke etc. have somewhat eluded my comprehension. Regards, Jonathan
we have a large scale application which a textbox has the status of many threads appended to it concurrently, and from different forms. this is a dumbed down version of it:
Public Sub addToMessageBox(ByVal msg As String)
If Me.InvokeRequired Then
Dim d As New AddToMessageBoxDelegate(AddressOf Me.addToMessageBox)
Me.BeginInvoke(d, New Object() {msg})
Else
Try
Me.MessageBox.AppendText("--" + msg + vbCrLf)
Catch ex As Exception
End Try
End If
End Sub
The delegate is declared at the begining
Private Delegate Sub AddToMessageBoxDelegate(ByVal msg As String)
the biggest difference that I can see is that I use the parent class's beginInvoke() and InvokeRequired(). I'd say give this a try. Call the parentClass.AddToMessageBox("Text you want to append") where you are calling the display().
Is there a way to start same Thread form foreach loop
Sub
For Each lvItem As ListViewItem In _ListView.SelectedItems
tThread = New Thread(AddressOf Me.myFunction())
tThread .Start()
Next
End Sub
Sub myFunction()
//Code
End Sub
In my case, when i select one item from list it is working fine...but when i select more than one files it odes not work.
I want to select multiple files (which are file paths) from ListView and convert them in mp3 files but with above solution. it converts first selected file successfully but then stops.
Creating a separate thread for each file is sub-optimal. In some cases, this can actually result in worse performance than doing them all sequentially, because your system will spend too much time switching back and forth between different threads. Instead, you want to choose a small number of threads and queue your items for time by those threads.
There are a lot of ways to implement this:
You can write custom code that bases the number of threads on the number of physical processor cores (greater of 2 or the number of cores - 1 is common). This is a lot of extra work, and is error prone.
You can use the built-in in ThreadPool.QueueUserWorkItem(). This is great, but it can be tricky to track progress of your items.
You can use the Task Parallel Library. This requires .Net 4, but it's probably your best option by far. The extra work upfront learning the concepts will also be a huge payoff, and it sounds like Microsoft is basing some of the more important features in .Net 5 around the Task concept.
I'm guessing that instead of having one variable tThread storing the thread, you probably meant to store all the threads, so instead have a List of them. So something like:
Sub
Dim threads as New List(Of Thread)
For Each lvItem As ListViewItem In _ListView.SelectedItems
tThread = New Thread(AddressOf Me.myFunction())
tThread .Start()
threads.Add(tThread)
Next
End Sub
Otherwise, if there's another issue, please supply more details.
Are you sure the items are selected? I tried the following with a few items in the listview and it worked as expected.
Private Sub Button2_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button2.Click
For Each lvItem As ListViewItem In ListView1.SelectedItems
Dim t As Threading.Thread = New Threading.Thread(AddressOf myFunction)
t.Start(lvItem)
Next
End Sub
Private Sub myFunction(ByVal lvi As Object)
Dim lvItem As ListViewItem = CType(lvi, ListViewItem)
Debug.WriteLine(lvItem.Text)
End Sub