I have an exceptionhandler function that basically just writes a line to a textbox on Form1. This works fine when being run normally but the second I use a thread to start a process it cannot access the property. No exception is thrown but no text is written to the textbox:
Public Sub ExceptionHandler(ByVal Description As String, Optional ByVal Message As String = Nothing)
' Add Error To Textbox
If Message = Nothing Then
Form1.txtErrLog.Text += Description & vbCrLf
Log_Error(Description)
Else
Form1.txtErrLog.Text += Description & " - " & Message & vbCrLf
Log_Error(Description, Message)
End If
MessageBox.Show("caught")
End Sub
Is it possible to access a form's properties from a thread this way or would it be easier to write to a text file or similar and refresh the textbox properties every 10 seconds or so (Don't see this as a good option but if it's the only way it will have to do!).
Also, still new to VB so if I have done anything that isn't good practice please let me know!
No, you shouldn't access any GUI component properties from the "wrong" thread (i.e. any thread other than the one running that component's event pump). You can use Control.Invoke/BeginInvoke to execute a delegate on the right thread though.
There are lots of tutorials around this on the web - many will be written with examples in C#, but the underlying information is language-agnostic. See Joe Albahari's threading tutorial for example.
You have to use delegates. Search for delegates in VB.
Here a peace of code that does the job.
Delegate Sub SetTextCallback(ByVal text As String)
Public Sub display_message(ByVal tx As String)
'prüfen ob invoke nötig ist
If Me.RichTextBox1.InvokeRequired Then
Dim d As New SetTextCallback(AddressOf display_message)
Me.Invoke(d, tx)
Else
tx.Trim()
Me.RichTextBox1.Text = tx
End If
End Sub
Related
I'm trying to create and call a custom event in the webbrowser control and everything that I've tried to do causes one error or another when the webpage executes the code. What I'm doing is adding a button on each row of a table to facilitate removing that row. However, the master list of data is in the application. When the script in the web page executes, I need to update the master list in the application. My thoughts were to call a custom event that will be fired in my application where I can do everything that I need to do. I just can't make this work. here are more details of what I have right now. Here is the html code for a given row:
Dim M As String = "</TD><TD>"
RetStr.Append("<TR ID='" & Me.Manifest & "' name='" & Me.Manifest & "'>")
RetStr.Append("<TD>").Append(CompanyID).Append(M).Append(CompanyName).Append(M)
RetStr.Append(ContactName).Append(M).Append(Address1).Append(M).Append(Address2)
RetStr.Append(M).Append(City).Append(M).Append(State).Append(M)
RetStr.Append(Zip).Append(M).Append(Phone).Append("</TD>")
RetStr.Append("<TD><button onclick='deleteRow(""" & Me.Manifest & """)'>Remove</button></TD>")
Return Replace(RetStr.ToString(), "<TD></TD>", "<TD> </TD>")
Here is the code that is in the function:
Dim HTMLOut As New List(Of String)
HTMLOut.Add("<HEAD>")
HTMLOut.Add(" <SCRIPT language=""VBScript"">")
HTMLOut.Add(" Function deleteRow(rowid)")
HTMLOut.Add(" set row = document.getElementById(rowid)")
HTMLOut.Add(" row.parentNode.removeChild(row)")
HTMLOut.Add(" dispatchEvent(Row)")
HTMLOut.Add(" End Function")
HTMLOut.Add(" </SCRIPT>")
HTMLOut.Add("</HEAD>")
HTMLOut.Add("<BODY>")
HTMLOut.Add(" <TABLE border='1' style='font-size:12;' NAME='Table' ID='TABLE'>")
Here is the code that I have in the application:
Private Sub WB_DocumentCompleted(sender As Object, e As
WebBrowserDocumentCompletedEventArgs) Handles WB.DocumentCompleted
WB.Document.AttachEventHandler("UpdateList", New EventHandler(
Function(ByVal s As Object, ByVal k As EventArgs)
MsgBox("BOO")
Return True
End Function))
End Sub
Any help in any direction, even if it means I need to change how I'm doing all of this, is very welcomed! There is more code then this, it's stripped down to what is needed to convey what I'm doing. I know I'm missing something, I just can't figure out what it is. The end goal is to update the master list in the application hosting the web browser; ideas suggestions and comments are always welcome. As a side note, I'm using the web browser control because the final part of the process is to create a file and sftp it to the vender (the application will do this), and print the report. Thanks!
I figured this out. I needed to create a class object, with the comvisible attribute set and add this to the objectForScripting property of the web browser control.
Imports System.Runtime.InteropServices
<ComVisible(True)> Public Class WBClassCode
Public Sub UpdateStuff(ByVal Data)
'My code goes here... called from the web page.
MsgBox("boo")
End Sub
End Class
I'm not able to update the TextBox content from another module.
The TextBox is in a Form called frm_main and the EventHandler in another module called md_zeiss.
Init() is called by a button on frm_main.
Problem:
If I directly call Test() from frm_main it does change the text.
If called by the event, it does not change the text, but displays the correct MessageBox.
Code:
Module md_zeiss
Sub Init()
Dim fsw As New FileSystemWatcher
fsw.Path = "C:\Output"
fsw.Filter = "*.txt"
fsw.NotifyFilter = NotifyFilters.Attributes Or NotifyFilters.CreationTime Or NotifyFilters.DirectoryName _
Or NotifyFilters.FileName Or NotifyFilters.LastAccess Or NotifyFilters.LastWrite Or NotifyFilters.Security Or NotifyFilters.Size
fsw.EnableRaisingEvents = True
AddHandler fsw.Changed, AddressOf md_zeiss.Main
End Sub
Sub Main(sender As Object, e As IO.FileSystemEventArgs)
Do While IsLocked(e.FullPath) = True
Application.DoEvents()
Loop
Dim fs As New FileStream(e.FullPath, FileMode.Open, FileAccess.Read)
Dim sr As New StreamReader(fs, System.Text.Encoding.Default)
Dim textline As String = vbNullString
Dim nr As String
Dim gi As String
Dim le As String
Do Until sr.Peek = -1
textline = sr.ReadLine
Select Case True
Case InStr(textline, vbTab & "Ø MOLDING_NR_SIDE" & vbTab)
nr = ReadVal(textline, 5)
Case InStr(textline, vbTab & "LENGTH" & vbTab)
gi = ReadVal(textline, 5)
Case InStr(textline, vbTab & "Ø MOLDING_GI_SIDE" & vbTab)
le = ReadVal(textline, 5)
End Select
Loop
Test()
End Sub
Sub Test()
frm_Main.TextBox1.Text = "Test"
MsgBox(frm_Main.TextBox1.Text)
End Sub
The FileSystemWatcher raises it events on a secondary thread by default. Default instances of forms are thread-specific so if you display the default instance of a form on the UI thread and then try to access the default instance from the handler of a FileSystemWatcher event (or a method called from that handler) then you're actually referring to two different form objects.
The simplest option is to set the SynchronizingObject property of the FileSystemWatcher on the UI thread. You can assign a form or other control to that property and the FileSystemWatcher will then raise its events on the thread that owns that control, i.e. the UI thread. If you do go down that route, just be sure that your event handler is executed quickly. You don;t want to tie up the UI thread with long-running code, which is why a secondary thread is used by default.
Another option is to use the SynchronizationContext class in your module to allow you to marshal a method call to the UI thread. You would continue to have the FileSystemWatcher raise its events on a secondary thread and do the background work there, then call Send or Post on the SynchronizationContext to invoke a method on the UI thread, where using the default instance of that form would refer to the same instance as you have already displayed.
Basically though, the architecture there is bad. You should almost certainly be using a class rather than a module and the form can then keep a reference to an instance of that class. The class could then raise an appropriate event that the form could handle and then the form could update its own TextBox. If you are access the controls on a form outside that form then the code is inherently bad. Default form instances make doing that easier, which is one reason that seasoned developers generally don't like them. They make it easier for beginners to get up and running, but it also makes it easier for beginners to paint themselves into a corner when things get remotely complex.
I've wrote a program which on startup loads the computer list from Active Directory. This takes about 10 seconds. If the user has started the program with a specific host as parameter, it should be usable immediately.
So to don't interrupt the user I want to load the computer list in a different thread. The problem is that it writes to a variable (the computer list) which is also used in the main thread.
You may think, I could simply use a temporary variable and when its done overwrite the main variable. But I have to keep existing data of the main variable.
'hosts list
Private Shared hosts As New SortedDictionary(Of String, HostEntry)
'Get all computers in Active Directory
'Will run in a extra thread
Private Delegate Sub GetADcomputersDelegate()
Private Sub GetADcomputers()
If Me.InvokeRequired Then
Me.Invoke(New GetADcomputersDelegate(AddressOf GetADcomputers), Nothing)
Else
lblStatusAD.Text = "Getting Computers..."
Try
Dim search As New DirectorySearcher(ActiveDirectory.Domain.GetCurrentDomain().GetDirectoryEntry(), "(objectClass=computer)")
For Each host As SearchResult In search.FindAll()
'AddHost creates a new HostEntry object and adds it to my "global" hosts variable
'It also checks if a host is already present in the list and only updates it.
AddHost(host.GetDirectoryEntry().Properties("cn").Value.ToLower(), host.GetDirectoryEntry().Properties("description").Value)
Next
Catch ex As Exception
Debug.WriteLine("GetADcomputers() Exception: " & ex.Message)
End Try
ThreadPool.SetMaxThreads(hosts.Count, hosts.Count)
Dim ah As String = activehost
'Fill my ListBox with the computers
lstHosts.DataSource = New BindingSource(hosts, Nothing)
'Select the computer that was selected before
UseHost(ah)
lblStatusAD.Text = ""
End If
End Sub
So when GetADcomputers() runs in its own thread, the main thread is also blocked. I guess because auf the hosts variable.
So what could I change to make the thread do it's work and after that apply the updated computer list without losing data of entries in old hosts list? And all this in a fast and efficient way.
That code is very wrong. If you call that method on a secondary thread then it immediately marshals a call back to the UI thread and does EVERYTHING on the UI thread. What you should be doing is executing all the background work on the secondary thread and then marshalling to the UI thread ONLY to update the UI.
Get rid of that If...Else block and just make the entire body of the method what's current ly in the Else block. Next, identify all the lines that specifically interact with the UI and remove each of those to their own method. You then add If...Else blocks to each of those methods so that only the code that actually touches the UI is executed on the UI thread.
Here's a start:
Private Sub GetADcomputers()
UpdateStatusADLabel("Getting Computers...")
Try
Dim search As New DirectorySearcher(ActiveDirectory.Domain.GetCurrentDomain().GetDirectoryEntry(), "(objectClass=computer)")
For Each host As SearchResult In search.FindAll()
'AddHost creates a new HostEntry object and adds it to my "global" hosts variable
'It also checks if a host is already present in the list and only updates it.
AddHost(host.GetDirectoryEntry().Properties("cn").Value.ToLower(), host.GetDirectoryEntry().Properties("description").Value)
Next
Catch ex As Exception
Debug.WriteLine("GetADcomputers() Exception: " & ex.Message)
End Try
ThreadPool.SetMaxThreads(hosts.Count, hosts.Count)
Dim ah As String = activehost
'Fill my ListBox with the computers
lstHosts.DataSource = New BindingSource(hosts, Nothing)
'Select the computer that was selected before
UseHost(ah)
lblStatusAD.Text = ""
End Sub
Private Sub UpdateStatusADLabel(text As String)
If lblStatusAD.InvokeRequired Then
lblStatusAD.Invoke(New Action(Of String)(AddressOf UpdateStatusADLabel), text)
Else
lblStatusAD.Text = text
End If
End Sub
I've been working through my first project and have had a great deal a valuable help from the guys on SO but now I'm stuck again.
The below sub is used to add TreeNodes to a TreeView, excluding certain filetypes/names, upon addition of new data:
Sub DirSearch(ByVal strDir As String, ByVal strPattern As String, ByVal tvParent As TreeNodeCollection)
Dim f As String
Dim e As String
Dim tvNode As TreeNode
Dim ext() As String = strPattern.Split("|"c)
Try
For Each d In Directory.GetDirectories(strDir)
If (UCase(IO.Path.GetFileName(d)) <> "BACKUP") And (UCase(IO.Path.GetFileName(d)) <> "BARS") Then
tvNode = tvParent.Add(IO.Path.GetFileName(d))
For Each e In ext
For Each f In Directory.GetFiles(d, e)
If (UCase(IO.Path.GetFileName(f)) <> "DATA.XLS") And (UCase(IO.Path.GetFileName(f)) <> "SPIRIT.XLSX") Then
tvNode.Nodes.Add(IO.Path.GetFileName(f))
End If
Next
Next
DirSearch(d, strPattern, tvNode.Nodes)
End If
Next
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
I'm now getting an error:
Action being performed on this control is being called from the wrong thread. Marshal to the correct thread using Control.Invoke or Control.BeginInvoke to perform this action.
On the following line:
tvNode = tvParent.Add(IO.Path.GetFileName(d))
Obviously, I understand its to do with 'threading' and the use of BeginInvoke / Invoke but even after reading the MSDN documentation on the error, I have no idea where to start.
This error only occurs, if I add a file to the initial directory (which is also the subject of a File System Watcher to monitor new additions).
Would someone be so kind as to give me an explanation in layman's terms so I may be able to understand.
This code is being run on a background thread where it's illegal to modify UI elements. The Invoke / BeginInvoke methods are ways to schedule a piece of code to run on UI thread where elements can be modified. For example you could change your code to the following
Dim action As Action = Sub() tvNode.Nodes.Add(IO.Path.GetFileName(f))
tvNode.TreeView.Invoke(action)
This code will take the delegate instance named action and run it on the UI thread where edits to tvNode are allowed
Fixing the earlier Add call is a bit trickier because there is no Control instance on which we can call BeginInvoke. The signature of the method will need to be updated to take a Dim control as Control as a parameter. You can pass in the TreeView for that parameter if you like. Once that is present the first Add can be changed as such
Dim outerAction As Action = Sub() tvNode = tvParent.Add(IO.Path.GetFileName(d))
control.Invoke(outerAction)
I'm not even sure I understand this situation enough to come up with a proper title. I come from a modest understanding of VB6 and having to climb a steep learning curve for VB 2010.
I am trying to create a multi-client server program that will communicate with my Enterprise iPhone app. I found a relatively simple example to build upon here: http://www.strokenine.com/blog/?p=218. I have been able to modify the code enough to make it work with my app, but with one glitch: I can't get access to the controls on the form to add items, even though the method is invoked within the form's class. (I tried this on the original code too, and it does the same thing. I don't know how the author managed to get it to work.)
Here's the code segment in question:
Public Class Server 'The form with the controls is on/in this class.
Dim clients As New Hashtable 'new database (hashtable) to hold the clients
Sub recieved(ByVal msg As String, ByVal client As ConnectedClient)
Dim message() As String = msg.Split("|") 'make an array with elements of the message recieved
Select Case message(0) 'process by the first element in the array
Case "CHAT" 'if it's CHAT
TextBox3.Text &= client.name & " says: " & " " & message(1) & vbNewLine 'add the message to the chatbox
sendallbutone(message(1), client.name) 'this will update all clients with the new message
' and it will not send the message to the client it recieved it from :)
Case "LOGIN" 'A client has connected
clients.Add(client, client.name) 'add the client to our database (a hashtable)
ListBox1.Items.Add(client.name) 'add the client to the listbox to display the new user
End Select
End Sub
Under Case "LOGIN" the code tries to add the login ID to the listbox. It throws an exception: "A first chance exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll" The listbox (all controls, for that matter) is in the same class, Server.vb and Server.vb [Design].
The data comes in from another class that is created whenever a client logs on, which raises the event that switches back to the Server class:
Public Class ConnectedClient
Public Event gotmessage(ByVal message As String, ByVal client As ConnectedClient) 'this is raised when we get a message from the client
Public Event disconnected(ByVal client As ConnectedClient) 'this is raised when we get the client disconnects
Sub read(ByVal ar As IAsyncResult) 'this will process all messages being recieved
Try
Dim sr As New StreamReader(cli.GetStream) 'initialize a new streamreader which will read from the client's stream
Dim msg As String = sr.ReadLine() 'create a new variable which will be used to hold the message being read
RaiseEvent gotmessage(msg, Me) 'tell the server a message has been recieved. Me is passed as an argument which represents
' the current client which it has recieved the message from to perform any client specific
' tasks if needed
cli.GetStream.BeginRead(New Byte() {0}, 0, 0, AddressOf read, Nothing) 'continue reading from the stream
Catch ex As Exception
Try 'if an error occurs in the reading purpose, we will try to read again to see if we still can read
Dim sr As New StreamReader(cli.GetStream) 'initialize a new streamreader which will read from the client's stream
Dim msg As String = sr.ReadLine() 'create a new variable which will be used to hold the message being read
RaiseEvent gotmessage(msg, Me) 'tell the server a message has been recieved. Me is passed as an argument which represents
' the current client which it has recieved the message from to perform any client specific
' tasks if needed
cli.GetStream.BeginRead(New Byte() {0}, 0, 0, AddressOf read, Nothing) 'continue reading from the stream
Catch ' IF WE STILL CANNOT READ
RaiseEvent disconnected(Me) 'WE CAN ASSUME THE CLIENT HAS DISCONNECTED
End Try
End Try
End Sub
I hope I am making sense with all this. It all seems to bounce back and forth, it seems so convoluted.
I've tried using Me.listbox1 and Server.listbox1 and several other similar structures, but to no avail.
I'm reading a lot about Invoke and Delegates, but would that be necessary if the method and the control are in the same class? Or do I have a fundamental misperception of what a class is?
Many thanks for any help I can get.
Private Delegate Sub UpdateListDelegate(byval itemName as string)
Private Sub UpdateList(byval itemName as string)
If Me.InvokeRequired Then
Me.Invoke(New UpdateListDelegate(AddressOf UpdateList), itemName)
Else
' UpdateList
' add list add code
ListBox1.Items.Add(itemName)
End If
End Sub
Add above, then replace:
ListBox1.Items.Add(client.name)
to
UpdateList(client.name)
Does it work? check the syntax, may have typo as I type it.