I am working with VB 2010 for an application which requires me to go back to a sub. After some digging, I found out GoSub is no longer supported. I tried using Goto but apparently you can't use it outside the sub the label is in. I tried calling the sub put the parameters were not known to me.
Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
I do not want to use the RunWorkerAsync because the worker will already be working. Please advise me on this matter.
It sounds like you are trying to solve a problem using procedural logic with an object-oriented tool.
If I understand you correctly, the sub is calling another section of code, and needs to return to the sub after it's finished. Make the called code itself a function or sub, and call it from the primary sub routine.
Related
I have declared a Sub that is meant to trigger when the listbox 'lstStudents' is double-clicked. However, it does not trigger when this happened. There can't be an error in the code itself as it is auto-generated. Why does the code not function as expected? The code is below:
Private Sub lstStudents_DoubleClick(sender As Object, e As EventArgs) Handles lstStudents.DoubleClick
Msgbox("test")
End Sub
The message box is only present for testing purposes.
Could You try to delete that previous "lstStudents" and add new one then apply the "ListBox1_DoubleClick" on it again to make sure it works.
Otherwise let us know what is going there because I think your code is normally and it should be working 100%.
I'm new to VB.NET threading
As for simple testing I tried the following, which I need to smoothly fill a listbox with values.
But it does not work as I expect, it hangs the interface. Please let me know what I'm doing wrong here.
Thank you.
Imports System.Threading
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim Thr As Threading.Thread
Thr = New Threading.Thread(New Threading.ThreadStart(AddressOf tprocess))
'Thr.SetApartmentState(ApartmentState.STA)
Thr.IsBackground = True
Thr.Start()
End Sub
Private Delegate Sub DoStuffDelegate()
Private Sub tprocess()
Dim i As Integer
For i = 0 To 20000
If Me.InvokeRequired Then
Me.Invoke(New DoStuffDelegate(AddressOf tprocess))
Else
ListBox1.Items.Add(i)
End If
Next
End Sub
End Class
When you write code to create a thread then you always have to worry about the kind of bugs that threading can cause. They are very hard to diagnose, the only decent way to address them is to know they exist and to write the code carefully so you know how to avoid them.
The most common threading bugs are threading races, deadlock and firehose bugs. You have the 1st and the 3rd bug in your code. You are complaining about the 3rd. Very quickly: the threading race bug is using Me.InvokeRequired. You have no guarantee that it is still true when the Me.Invoke() statement executes. This goes wrong when the user closes the window while your thread is still running. When you try to fix this problem you'll get to see what the 2nd bug looks like. But you are not there yet.
The firehose bug is the Me.Invoke() call. Very fast, takes less than a microsecond of work for the worker thread, you do it 20000 times at a very high rate. It is however another thread that must actually do the work of adding the item, your UI thread. That is not fast, it not only has to add the item but it also needs to repaint the control. Many microseconds.
While this goes on, your UI thread is burning 100% core, trying to keep up with the relentless rate of invoke requests. Working as hard as it can to add items to the listbox. Something has to give, while it is doing this it is not taking care of the lower priority jobs it has to do. Painting and responding to user input. In effect, your UI looks completely frozen. You can't see it paint anymore and trying to, say, close the window doesn't work. It isn't actually dead, it is hard at work.
Takes a while, probably a few handful of seconds, give or take. Until the worker thread finishes its for() loop and stops slamming the UI thread with invoke requests. And everything turns back to normal.
A firehose bug like this is pretty fundamental. The only way to fix it is to call Invoke() less often or at a lower rate. Note how putting Thread.Sleep(50) after the Invoke() call instantly fixes it. But of course that slows down your worker thread a lot. You call Invoke() less often by using AddRange() instead of Add(), adding (say) 1000 items at a time. Which is the proper fix but now it becomes fairly pointless to still try to update the listbox from the worker thread. Might as well do it with a single AddRange() call. The quickest way.
Try changing:
Thr = New Threading.Thread(New Threading.ThreadStart(AddressOf tprocess))
to this:
Thr = New Threading.Thread(AddressOf tprocess)
ThreadStart will start that thread immediately
I tried the following way. It's almost easy for me to handle. Backgroudworker manages this situation perfectly well.
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim i As Integer
For i = 1 To 20000
BackgroundWorker1.ReportProgress((i / 20000) * 100, i)
Threading.Thread.Sleep(1)
Next
End Sub
Private Sub BackgroundWorker1_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
ProgressBar1.Value = e.ProgressPercentage
ListBox1.Items.Add(e.UserState)
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
MsgBox("Complete")
End Sub
I'm currently creating my application and I'd like to write an understandable code.
I'd like to know when to create a procedure. If it affects the performance of my application if I created much.
Here is my sample:
Sample Code:
With Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Greetings()
End Sub
Private sub Greetings()
MessageBox.Show("Hello!")
MessageBox.Show("To")
MessageBox.Show("My")
MessageBox.Show("World")
End
In the example above, assume that this sub will only be called 1 - 2 times in the whole application. I like to easily understand my code.
Versus
Without Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
MessageBox.Show("Hello!")
MessageBox.Show("To")
MessageBox.Show("My")
MessageBox.Show("World")
End Sub
In the example above, this piece of code too my time to understand.
In general, you should create subroutines when the logic is going to be used multiple times, especially if it's being used in multiple places.
If you ever have to change code, you want to only change it ONCE.
Performance with running basic code or calling functions is a non-issue. Do not even consider it.
I'm looking to call a pre-existing event handler subroutine from the form_Load event handler.
But the below doesn't work because control doesn't come back and I want to do more.
UPDATE:
I'm new to this so I don't know what the proper protocol is but...
The reason for the non-return was that a statement like the below ended the subroutines execution.
If aLabel.Tag = 1...
the fix was adding New to the declaration to create an instance of it, ie..
changing....
Dim aLabel As Label
... to ...
Dim aLabel As New Label
I'm surprised I didn't get a warning but instead they just abruptly stopped execution of the sub. That wasn't very helpful :)
Thanks again for your time guys...
(Maybe this question should be deleted now that it has served its purpose)
#konrad #karl
END OF UPDATE
What doesn't work is....
Private Sub Form1_Load...
button1_Click(sender, e) 'But Control doesn't come back.
end sub
Do I change the sender to something?
Thanks in advance
Dave
Invoking event handlers like this is a bad idea, because you are trying to simulate the event context by making sender and/or EventArgs be something else.
Instead, put the logic that you want to invoke into a Subroutine or Function and have your Form1_Load method call that; likewise if you really do have a real click event handler, then that handler code can call the method too, like this:
Private Sub Form1_Load()
DoSomeWork()
End Sub
Protected Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs)
DoSomeWork()
End Sub
Private Sub DoSomeWork()
' Put logic here that you want to do from form load and a button click
End Sub
This has the benefit of making the code cleaner, clearer and easier to maintain as you only need to change the logic in one place should you need to change the logic.
Note: Obviously, you can pass parameters to the DoSomeWork method, if need be, and change it to a Function if you need it to return something.
I have translated some code from C# to VB.net for the purpose of getting Folder Browser functionality. The link to the code is here.....
http://www.codeproject.com/KB/aspnet/DirectoryBrowsing.aspx
My issue is that I have not been able to correcly translate these two lines of code to VB.net.
TreeView1.TreeNodeExpanded +=new TreeNodeEventHandler(TreeView1_TreeNodeExpanded);
TreeView1.SelectedNodeChanged += new EventHandler(TreeView1_SelectedNodeChanged);
Every translator I have used has simply dropped the semicolon from the end of each line. But the editor still does not like them.
I could some help with this as it seems this effects the refresh of the selected folder in the tree view control.
I don't get to see the C drive folder unless I type the path in the text box, and the folder will still not expand.
thank you,
Use this:
AddHandler TreeView1.TreeNodeExpanded, AddressOf TreeView1_TreeNodeExpanded
AddHandler TreeView1.SelectedNodeChanged, AddressOf TreeView1_SelectedNodeChanged
Edit:
A different way to do this would be to apply it at the method level:
Protected Sub TreeView1_TreeNodeExpanded(ByVal sender as Object, ByVal e as TreeNodeEventArgs) Handles TreeView1.TreeNodeExpanded
' Some code
End Sub
Protected Sub TreeView1_SelectedNodeChanged(ByVal sender as Object, ByVal e as EventArgs) Handles TreeView1.SelectedNodeChanged
' Some code
End Sub
You should run this in debug to find out what exactly is going on. I find a lot of times when events of this nature are run in asp.net, you have a conflicting event that "resets" the controls you are attempting to change.