I'm trying to build a small application that connects to a couple databases to move data from one to the other, manipulating and verifying data is it moves. I had everything working, but wanted to add the majority of the work to a second thread so that the initial window is still functional.
I have most of it working fine so far, except for one pesky bit. I allow the user to choose the database from a list of databases on a MSSQL Server. Without the threading, the program can read the text of the combo box without issue. As soon as I add in threading, it can't read the text of the combo box. It doesn't have issues reading the text boxes that contain the servername/username/password, just with this one combo box. The code below is in a class that handles all my database functions. The combobox is on the main form (frmMain) that is launched when you run the application. frmMain is the default form for the application.
Without threading I was doing this.
Me._sqlDB = New sqlDatabase
Me._sqlDB.DBServer = frmMain.txtServer.Text
Me._sqlDB.DBUsername = frmMain.txtUser.Text
Me._sqlDB.DBPassword = frmMain.txtPassword.Text
Me._sqlDB.DBDatabase = frmMain.cboSQLDatabase.Text
When I added the thread, it couldn't read from the combo box (along with a host of other issues due to non-threadsafe calls). I did some research and added in some delegates and invokes. This solved the rest of the issues I was running into, but the combobox was still unreadable.
I created a function with a delegate to read the combobox, hoping that it was a thread related issue, but still no luck. The database connection setup code is in the database class I mentioned above and the GetDatabaseName function is in the main form (frmMain).
'Database Connection Setup
Me._sqlDB = New sqlDatabase
Me._sqlDB.DBServer = frmMain.txtServer.Text
Me._sqlDB.DBUsername = frmMain.txtUser.Text
Me._sqlDB.DBPassword = frmMain.txtPassword.Text
Me._sqlDB.DBDatabase = frmMain.GetDatabaseName
'GetDatabaseName Function for Connection String Setup
Delegate Function GetDatabaseNameDel() As String
Public Function GetDatabaseName() As String
Dim DBName As String = ""
If Me.cboSQLDatabase.InvokeRequired Then
DBName = Me.Invoke(New GetDatabaseNameDel(AddressOf GetDatabaseName))
Else
DBName = Me.cboSQLDatabase.Text
End If
Return DBName
End Function
I have tried several of the combobox properties, including SelectedItem, SelectedText, and Text. None of them have any value when the GetDatabaseName function is called. In fact, when run in debug mode and pausing the code execution, Visual Studio shows that the combobox has nothing in it (Count = 0, Items collection is empty).
The combobox is populated using a SqlDataReader that reads the list of database names from the server.
I also tried changing the setup to use a BackgroundWorker, but I get the same results.
Any thoughts on why the combobox is appearing as empty when running as a separate thread?
With a little more research, I found a possible solution, but it seems really janky. If I change the call to the function to use this:
Me._sqlDB.DBDatabase = CType(My.Application.OpenForms.Item("frmMain"), frmMain).GetDatabaseName
It works, but this seems like a very odd workaround for the issue. Is there a better way to refer to the control on the active form?
Related
How can I stop Access from prompting "Do you want to save changes to the layout of query" when I try to close a form that has a subform in datasheet view?
I have a form with a subform in Datasheet view with the .SourceObject set to a temporary pivot / crosstab query (no actual form object). If the user changes the width of a column and closes the window with the built-in Access close button, the user (and annoyed developer) is always presented with the "Do you want to save changes to the layout of query" prompt.
I am able to avoid this prompt by setting MySubform.SourceObject = "" in the click of my Close button but anyone clicking the [x] button or pressing CTRL+F4 or CTRL+W gets the prompt.
I have put breakpoints in the Form_Close and Form_Unload events but this prompt appears before they fire.
I want to clarify further that this subform object is Unbound and not based on a form object. I am building a dynamic Crosstab SQL statement, creating a QueryDef with the SQL, and then setting MySubform.SourceObject = "query.qry_tmp_Pivot" This is a neat technique for a crosstab/pivot query because the columns can vary and I don't think a form object would support that.
I am able to use the Watch window on the MySubform object and I can see that a MySubform.Form object exists. It has a Controls collection containing a control for all of the columns in my query. I have an optional routine that I can run that will loop through all of the controls and set their .ColumnWidth = -2, which will auto-size the column width based on the widest data of the visible rows in the datasheet. When this routine was running I was noticing that every time I closed the form (not using my Close button) I was getting the save prompt. I have disabled this routine for debugging but a user will still get the prompt if they manually adjust any column width.
I feel like I need to explain this extra detail so you realize this is not an Access 101 issue. You probably know that if you've read this far. Here's another thought I had: Maybe I could trap the Unload event in the subform control before the prompt happens. Because there is no true Form object to put test code in, I created a class object and passed MySubform to it. The class uses WithEvents and creates events like OnClose and OnCurrent on the class module's mForm object. Sample class code is below.
Private WithEvents mForm As Access.Form ' This is the form object of the Subform control
Public Sub InitalizeSubform(Subform As Access.Subform)
Set mForm = Subform.Form
Debug.Print Subform.Name, mForm.Name, mForm.Controls.count
' Create some events to intercept the default events.
mForm.OnClick = "[Event Procedure]"
mForm.OnClose = "[Event Procedure]"
mForm.OnUnload = "[Event Procedure]"
mForm.OnCurrent = "[Event Procedure]"
End Sub
Private Sub mForm_Click()
Debug.Print "Clicking " & mForm.Name
End Sub
Private Sub mForm_Current()
Debug.Print "On Current " & mForm.Name, "Record " & mForm.CurrentRecord & " of " & mForm.RecordsetClone.RecordCount
End Sub
Private Sub mForm_Unload(Cancel As Integer)
Debug.Print "Unloading " & mForm.Name
End Sub
Private Sub mForm_Close()
Debug.Print "Closing " & mForm.Name
End Sub
The VBE Watch window shows my new events on the mForm object but unfortunately they never fire. I know the class works because I used it with a bound subform and all of the events are intercepted by the class. I'm not sure what else to try.
Events on the subform never fire because it's a lightweight form (without a module). See this Q&A and the docs. Lightweight forms don't support event listeners, but do support calling public functions from an event, e.g. mForm.OnClick = "SomePublicFunction()"
Note that the workaround described in this answer also opens up the possibility of displaying a crosstab query in a form without saving it at all.
Alternatively, you could try capturing the event on your main form, and suppress saving there.
I gave answer credit to #ErikA for this question. He directed me to an answer to a somewhat related question here which is what I ended up implementing and it works. His instructions were very straightforward and easier to implement than I first anticipated.
The answer to my question seems to be that it may not be possible to avoid the save prompt when using a lightweight form object. If someone comes along with a solution I'd still like to hear it.
What I learned from this experience:
An unbound subform that has its .SourceObject set to a table or query will not have a code module. This considered to be a lightweight object.
Public functions can be added to event properties on lightweight forms but they don't seem to fire before the save prompt appears as the parent form is closing.
Binding a pivot query or temp table to a real form object that has 254 controls on it is the only way I found that doesn't prompt to save design changes when the parent form closes. Mapping the query/table columns to the 254 datasheet controls is super fast.
A class is a nice way to intercept events if you're not using a lightweight object. A class also lets you open multiple instances of the same object.
I ended up not implementing my solution without using a class because there were no events I needed to capture. At this point I don't need my frmDynDS to be used for other purposes and I'd like to keep the object count down (this is a large app with 1400+ objects).
I put the following code in a function that gets called when the subform is loaded or refreshed.
With subCrosstab
' Set the subform source object to the special Dynamic Datasheet form. This could be set at design time on the Subform control.
.SourceObject = "Form.frmDynDS"
' Run the code to assign the form controls to the Recordset columns.
.Form.LoadTable "qry_tmp_Pivot" ' A query object works as well as a table.
' Optional code
.Form.OnCurrent = "=SomePublicFunction()"
.Form.AllowAdditions = False
.Form.AllowEdits = False
.Form.AllowDeletions = False
.Form.DatasheetFontHeight = 9
End With
I can now resize the columns and never get a prompt to save layout changes no matter how I close the parent form.
I would like to have a subroutine in VBA that conditionally changes the Enabled property of each of 20+ buttons on a form via iteration rather than code them all by hand. These buttons are named similar to tables that they process. For example: A table to process is called "CUTLIST"; its corresponding button is called "but_CUTLIST". There is another table that holds the list of tables to be processed (used for iteration purposes in other subs).
What I have so far...
Private Sub txt_DataSet_GotFocus()
Dim sqlQry as String
Dim butName As String
Dim tableList As Recordset
Dim tempTable As Recordset
Set tableList = CurrentDb.OpenRecordset("TableList") 'names of tables for user to process
tableList.MoveFirst 'this line was corrected by moving out of the loop
Do Until tableList.EOF
sqlQry = 'SQL query that determines need for the button to be enabled/disabled
Set tempTable = CurrentDb.OpenRecordset(sqlQry)
If tempTable.RecordCount > 0 Then
'begin code that eludes me
butName = "but_" & tableList!tName
Me(butName).Enabled False
'end code that eludes me
End If
tableList.MoveNext
Loop
End Sub
If I remember correctly, JavaScript is capable of calling upon objects through a variable by handling them as elements of the document's object "array." Example: this[objID]=objVal Is such a thing possible with VBA or am I just going about this all wrong?
Viewing other questions... is this what's called "reflection"? If so, then this can't be done in VBA. :(
In case more explanation helps to answer the question better... I have a utility that runs SQL queries against a pre-defined set of tables. Each table has its own button, so that the user may process a query against any of the tables as needed. Depending on circumstances happening to data beforehand, any combination of the tables may need to be queried via pressing of said buttons. Constantly referring to the log, to see what was already done, gets cumbersome after processing several data sets. So, I'd like to have the buttons individually disable themselves if they are not needed for the currently focused data set. I have another idea on how to make that happen, but making this code work would be faster and I would learn something.
I'm not an expert on VBA, but I would re-arrange the code to take advantage of the fact that you can iterate through the control collection in the user form
Something like this:
Dim ctrl as Control
For Each ctrl in UserForm1.Controls
If TypeName(ctrl) = "Button" Then
ctrl.Enabled = True
End If
Next
You can pass the button name to some other function (from this loop) to determine whether the button in question should be enabled / disabled.
I am currently making a vb program that i plan to make very big. I have a decent knowledge of visual basic but today i came across something i do not understand. Because of the huge size of my program , i decided to try and keep the program as organized as possible by putting specific subs in modules. These subs consist of httprequest , webbrowsers(control), webclients and alot of loops. In order to prevent these subs from lagging my main application i thread them using threading.thread and i start them from my main form. But this leads to two problems.
Problem 1: The threads cannot in any way interact with the main form.
Once the a httprequest or webclient collects the information from my desired website, i am trying to make it add the info to a listbox in my main form, So what i did is it typed
Msgbox("Info Sent")
form1.listbox1.items.add(String)
The first messagebox will show but although the code right under it runs, nothing is added to the first forms listbox.I am not using delegates to transfer the information, instead, although its not a good habit, i am using checkforillegalcrossovers.
Problem 2: Threading with a webbrowser.
Threading with a webbrowser using threading.thread also does not work because it causes an active x error. After looking it up i found that a solution was to use a single threaded apartment but this would not work because i may need multiple threads running off the same sub at once.
One solution that i have found to this problem is creating another form completely and setting it invisible, and since the form is its own thread i do not need to use threading.thread , but the problem comes when i am trying to create multiple threads, or else i can somehow dynamically create the threads and put the subs inside of it programically this method wont work And even if it does i feel that it is sloppy so i will leave this for one of two last resorts.
The other solution is the most simple one in which i just put all of the code in the main form, but if i keep on doing that form1 is gonna become huge and sloppy, doing this wont solve the webbrowser problem either and even when using regions i still feel that something that 1000+ lines deserves its own class.
There must be some solution out there that solves these problems. Any help would be appreciated, Thanks.
I checked my code for updating the progress bar, and using a single thread with synclock will NOT work. They way I make it work is perform the step of the pbar each time after a thread is started as I have limited total threads (say less than 5 threads). Thus, even the progress bar steps before the threads are finished, but it will not progress further before new threads started. It is not 100% accurate but it more or less telling the progress
'update the progress bar
some_form.PBar1.PerformStep()
' This while loop is to count the existing running thread,
' and determine whether new thread should start
While 1
Dim t2 = New System.Threading.Thread(Sub() WaitForPermission())
t2.Start()
t2.Join()
If proceed_gen Then
Exit While
End If
End While
'Start doing what I need to do
Dim t1 = SomeSub()
t1.Start()
'End of code, as VB doest not have thread.detach()
Correct me if I am wrong, but you probably have to use a background worker. I know this is annoying, but this is the limitation of VB.net.
Or, you can have something like this (pseudo code, not tested)
structure some_struct
'define the strings you want to update, and their status such that
'main() knows if you need to update the stuff to the form
' You can also put how many threads are running, and the status of each thread,
'such that the main knows if all threads are completed
end structure
sub your_sub()
'Manipulate the website, and update the data structure with
'proper stuff you need
end sub
sub main(){
dim t1 = New System.Threading.Thread(Sub() your_sub())
t1.start()
' I am listing only one threads here, but start as many as you want
'check if there are strings that you need to update to the form
while 1
'check if there are any stuff you want to update from the data structure.
' Make sure you use synclock on the data structure, so each thread won't fight each other on accessing the data struct
dim should_update as boolean = false
should_update = 'Something thatyou should implement to judge whether you should update the form.
'You can start a thread and join it so the thread won't fight with other threads for accessing the data structure
dim some_string as string
if should_update
some_string = 'You may also need a thread to join to get the stuff you need. Dim the string as an array if it is required.
'You can also try pass by ref
'if you need to use thread to access the data structure to know if you need to update the form
form1.listbox1.items.add(some_string )
end if
end while
end sub
This is an ugly solution, but it will help you do the job...
How can I set the FocusedItem property programatically?
I've tried this so far with no success:
If lvw.FocusedItem Is Nothing Then
If lvw.Items.Count > 0 Then
lvw.Focus()
lvw.HideSelection = False
lvw.Items(0).Selected = True
lvw.Items(0).Focused = True
lvw.FocusedItem = lvw.Items(0)
lvw.Select()
End If
End If
btw the form where the listview is has not called the ShowDialog method yet.
Can this be the reason for this not to work?
You have to understand that each control on the Form and the Form itself is a window and for the window to have focus it must first be created and assigned a handle.
For a basic description of this, I refer you to: All About Handles in Windows Forms The following excerpts are from the referenced article.
What is a Handle?
A handle (HWND) is the return value from CreateWindowEx which the Windows Operating System uses to identify a window. A "window" in win32 is a much broader concept than you may think - each individual button, combobox, listbox etc comprises a window. (For more information see About Window Classes ) NOTE: there are other things known as "Handles" in the Framework - e.g. GDI Handles from a Bitmap or Handles to Device Contexts (HDCs) - this article discusses HWNDs only.
...
When does a Control create its handle? (When does a control call CreateWindowEx?)
A control tries as much as possible to defer creating its handle. This is because setting properties forces chatty interop between the CLR and user32.
Typically the handles for all the controls are created before the
Form.Load event is called. Handles can also be created if the "Handle"
property is called and the handle has not yet been created, or
CreateControl() is called.
So a window's handle is not immediately created when you instantiate a control. However, you can force a control to create its handle by referencing its Handle property.
So if you first get the ListView to create its handle, then when you set those properties that you wanted.
Dim f2 As New Form2
' you do not need this condition, it is here only for demonstration purposes
' so that you can step through the code in the debugger and observe the
' code execution.
If Not f2.ListView1.IsHandleCreated Then
' retrieval of the Handle will cause a handle to be created
' if it has not yet been created
' if you delete the If-Then block, you will need to retain the
' following statement
Dim h As IntPtr = f2.ListView1.Handle
End If
f2.ListView1.FocusedItem = f2.ListView1.Items(2)
f2.ListView1.Items(2).Selected = True
f2.ListView1.Items(2).Focused = True
f2.ActiveControl = f2.ListView1
f2.ShowDialog()
As others have commented, your code should work as written. If all you need is to programmatically access the focused item in your code, you shouldn't be experiencing any difficulties. (If you are, please describe them.)
If you are looking for a visual effect (the row being highlighted), my guess is that your code is in another control's event and the focus is being set back to that control automatically the instant after your code runs. More than likely your code needs to be where it is and trying to move it elsewhere to prevent this issue would be a waste of time.
However, there are other ways to set a row apart visually. When a list view isn't likely to stay focused, my preferred method is to distinguish the selected item with a different fore/back color. (You can use the focused item if you prefer, but I find the selected item more useful. Your call.)
Here is an example which visually highlights the selected row, regardless of focus:
Private Sub lvw_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lvw.SelectedIndexChanged
If lvw.Items Is Nothing Then Exit Sub
For Each lvi As ListViewItem In lvw.Items
If lvi.Selected = True Then
lvi.ForeColor = Color.DarkGray
lvi.BackColor = Color.LightCyan
Else
lvi.ForeColor = Color.Black
lvi.BackColor = Color.White
End If
Next
End Sub
EDIT:
In response to the added information that this form is being displayed using ShowDialog, yes, that is likely the source of your problem.
ShowDialog creates a new instance of the form. Therefore, if you have set any properties of a form or its controls, and later call ShowDialog to display that form, the form displayed is a new copy of the original form and will not reflect the changes you made programatically.
Imagine you sit down at a computer where a blank Word document is already open. You type something in it and then open a new document. The text you typed in the first document is not copied to the second. I think this is the root of your troubles here.
I have VisualBasic project wih many forms,and one of it is form1.Whenever the initializecimponent method is called,VS stops responding and i have to end it using taskmgr.The bug is inside the form1.designer.vb, because i am able to view and edit other forms and usercontrols in designer.Anoter strange thing is that the stand alone exe runs successfully outside the IDE.I also tried adding the form to another project and that project too crashes.Whenever i build/debug/view form1 in designer, i get two dialogs one after the other:VS2010 has stopped working, VS2010 is restarting( but it never does!)
Create a copy of the form, and begin removing parts of the form until it works. The last thing you removed is what failed. You'll have to do this manually by removing three parts of each control:
The Declaration (at the bottom)
The instantiation (at the top)
The configuration (in the middle). Below is an example of the configuration
'
'LeftLabel
'
Me.LeftLabel.Anchor = System.Windows.Forms.AnchorStyles.Left
Me.LeftLabel.AutoSize = True
Me.LeftLabel.Location = New System.Drawing.Point(3, 3)
Me.LeftLabel.Name = "LeftLabel"
Me.LeftLabel.Size = New System.Drawing.Size(39, 13)
Me.LeftLabel.TabIndex = 1
Me.LeftLabel.Text = "Label2"
You'll also need to remove any references to that control, such as it being added to a container.
Do this one control at a time, then build the project and open the form. If the form does NOT open, restart visual studio and do the next control. if it DOES open, then the last thing you removed was the culprit.
For programmers facing the same problem, here is the solution:
Make sure that your user controls doesn't creates instances of themselves inside themselves.even though your program might run without any error, VS designer will crash.here is an example for such kind of code:
Public class controlx
public sub new()
dim x as new controlx
End sub
End class
you might think its a silly logical error, but such errors can be very much frustrating and time consuming.always breakdown your code to smaller units so that its manageable as Brian said.