My code is designed to be a control system for a 2-axis motion system. I have 2 drives that each output a count of their steps. I can read the device, update a property, and update the text field of a label. However, it does not update the form. When I use a message box, I can display the text value being correct, but nothing updates the label.
I'm happy to try any suggestions, but I've been fighting this for about 16 hours and I'm at my wits end - as evidenced by the clear overkill/terrible coding that is shown in the code. I can't understand why it's not updating.
Additionally, a manual button with all versions seen below to refresh a form doesn't update the control.
Direction, recommendations?
Private Sub PositionChanged(ByVal sender As Object, ByVal e As EventArgs)
If TraverseController.InvokeRequired Then
TraverseController.Invoke(
New EventHandler(Of EventArgs)(AddressOf PositionChanged), sender, e)
Return
End If
'RaiseEvent PropertyChanged(TraverseController, New System.ComponentModel.PropertyChangedEventArgs("Position"))
MessageBox.Show(TraverseController.lblLinearDrivePosDisp.Text)
TraverseController.lblLinearDrivePosDisp.Text = CStr(_position)
Application.DoEvents()
TraverseController.lblLinearDrivePosDisp.ResetBindings()
TraverseController.GBDrivePositionDisp.Refresh()
TraverseController.lblLinearDrivePosDisp.Refresh()
TraverseController.Refresh()
TraverseController.Invalidate()
TraverseController.Update()
Application.DoEvents()
MessageBox.Show(TraverseController.lblLinearDrivePosDisp.Text)
End Sub
Assumption: TraverseController is form's class name.
This looks like a VB default form instance issue. It is apparent that you are trying to properly marshal control interaction back to the UI thread by using checking TraverseController.InvokeRequired. However, due to the way these default instance are created, TraverseController.InvokeRequired is creating a new instance of TraverseController on the secondary thread and all subsequent code is modifying that instance and not the one created on the UI thread.
One way to deal with this is to pass a synchronizing control instance to the class where PositionChanged changed method is defined and check that control's InvokeRequired method instead of TraverseController.InvokeRequired. If the containing class is itself a UI control, then use that class instance (Me.InvokeRequired).
How can I restart a running VB program from within?
I have written a VB program that solves SUDOKU puzzles.
When it completes the solution, it asks if the user wants to run again with another puzzle.
I can not:
-determine the first line of code that the program executes. The main() is empty. All code is on the tab for Form1. I have tried breakpoints, but still can't determine the starting point.
-figure out how to cause the program to jump back to the starting point in the code.
Can you help me?
I've tried placing breakpoints in the code at places that might be close to the starting point, but so far that hasn't worked. When the program starts, Form1 is displayed, and it is waiting to see if a check box gets activated, or if text is entered anywhere in many text boxes.
You should do what Alejandro said in his comment: "reset the data state to the starting point".
But if you must, you can restart a WinForms application with Shell(Application.ExecutablePath)
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If MessageBox.Show("Start from scratch?", "Confirm Restart", MessageBoxButtons.YesNo, MessageBoxIcon.Question) = DialogResult.Yes Then restart()
End Sub
Private Sub restart()
Shell(Application.ExecutablePath, AppWinStyle.NormalFocus, False)
End
End Sub
Consider a simple .NET form with a couple of radio buttons and a checkbox.
Each of the radio buttons has a CheckedChanged handler setup that performs some action based on the state of the checkbox.
My problem is, when I initialize on the default radiobutton to be checked (from the designer properties window) the CheckedChanged event is fired for that radio button, but the Checkbox hasn't been initialized yet so I either get a null pointer exception or the wrong value is used in the handler. Either way, I don't want that handler code to be run unless the user picks a radio button after the form has been loaded.
I currently get around this by not initializing the radio button, but I need to set that default eventually and the best place is from the designer. I also can add a boolean field that's not set to true until the form is fully loaded and not process the events if that is false, but it's a dirty hack.
What can I do to prevent that handler from running its code?
To make it feel slightly less dirty, if you initialize the controls in the constructor of the form you might be able to use the forms IsHandleCreated property rather than your own bool to check if it should actually validate or not.
I would think that normally you wouldn't want to validate anything before it's been shown for the first time and handle isn't created until it is.
Code Example:
Private Sub myRadioButton_CheckedChanged(sender As Object, e As EventArgs) Handles myRadioButton.CheckedChanged
If myRadioButton.Checked AndAlso myRadioButton.IsHandleCreated Then
'Do Work
End If
End Sub
"I also can put a boolean field that's not set to true until the form is fully loaded and not process the events if that is false, but it's a dirty hack."
It's also the easist and best way to do it!
Lets say .NET provides a neat way to turn an and off all the event handlers until the form is loaded. Even just the ones YOU are handling. It would still not be sufficiently flexible to disable what you wanted to enable but disable what you didn't. Often form setups happen and you want the events to fire. Also the form won't build right if no events fire.
The easy solution is to declare an initializing variable:
Private Initializing as boolean = True
Private Sub rb_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles rbNuevos.CheckedChanged, RbDesaparecidos.CheckedChanged, RbModificados.CheckedChanged, RbNoDesap.CheckedChanged, RbDesHoy.CheckedChanged, RbChT.CheckedChanged
if Initializing then return
'Your Code
End Sub
Public Sub New()
' Llamada necesaria para el Diseñador de Windows Forms.
InitializeComponent()
' Agregue cualquier inicialización después de la llamada a InitializeComponent().
initializing = false
end sub
Most sophisticated: Remove the "handles" from the method, and use AddHandler on the new method.
Public Sub New()
' Llamada necesaria para el Diseñador de Windows Forms.
InitializeComponent()
' Agregue cualquier inicialización después de la llamada a InitializeComponent().
AddHandler RbChT.CheckedChanged, AddressOf rb_CheckedChanged
end sub
For radiobutton see Hans Olsson answer
For numeric up down, do it like this
Private Sub myNumeric_ValueChanged(sender As Object, e As EventArgs) Handles myNumeric.ValueChanged
If myNumeric.Value >= 0 AndAlso myNumeric.IsHandleCreated Then
'Do the work
End If
End Sub
The keyword is myNumeric.Value and IsHandleCreated
Yet another way:
Private Sub dgvGroups_CellValueChanged(sender As System.Object, e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgvGroups.CellValueChanged
If Me.Visible = False Then Exit Sub ' Sub gets called on form load which causes problems
wksGroups.Cells(e.RowIndex + 1, 1) = dgvGroups.Item(e.ColumnIndex, e.RowIndex).Value
wksGroups.Cells(1, 5) = dgvGroups.RowCount
One thing I've found that works is adding the events manually after you load the form.
To do this you can simply go into the generated form code found in the designer file of that form, and pull out the lines that add the event. It would look something like this:
this.controlName.CheckedChanged += new System.EventHandler(this.controlName_CheckedChanged);
Then put all of these calls into a method that you call after the InitializeComponent call in your form's constructor.
Just in case anyone is still searching for this the event is fired upon initializing the form BUT the form is not yet visible, Also Say that you have a foreign key relationship upon which you have a default value needed issue that gets fired every row update too. So the following code worked for me....
if (Visible && !(e.ColumnIndex == 0))
{
phoneEdited = true;
MessageBox.Show("A Phone entry has been entered");
}
Don't set checked on a control that really does much in designer.
The global flag and conditional exits where needed.
Try..Catch the sore spots to ignore a meaningless exception.
(Using VS 2017) It appears to me that it is an annoyance but not a bug. It is consistent with the model in use. The event is fired by normal operation of code, but code I did not write (but can access where fools fear to tread) and where there appears to be no (decent) place earlier in the normal flow to anticipate it.
The cleanest answer seems to be not to check radio button or checkbox controls in the designer at all if they trigger any significant code. Instead these controls should be changed by code (e.g. checked = true) in the Load event (for example) AFTER all the initialization is done.
There is no loss of flexibility here since both are fixed before the build, only in different places. The event handlers will handle it exactly as if a user had clicked the control in the natural flow of a well designed GUI application. (This reminds me of the ancient RPG proverb "Don't buck the cycle". (Anyone here remember RPG? I, not part of IBM-oriented team, never used it but had interesting discussions with some who did. ) Pre-checking controls hits the wrong part of the VS cycle.)
If for any reason that will not work, the next best thing is the kludge suggested elsewhere of a single status boolean initialized false and set true at the appropriate time with conditional exits in the necessary places to prevent them from crashing until then. It will get the job done, but it's ugly. Better than failure.
Another thing I tried before I decided that designer level pre-set checks were the problem and there was a very acceptable alternative was to put the danger spots in a Try..Catch to be able to ignore the exception. Also a kludge.
For the cleanest code, reverse the True/False approach used in some other examples. Focus on 'ready' rather than 'busy'. Here's an example for a Windows Form:
At the Class level, add Private app_ready As Boolean (it will be False by default).
At the end of the Form.Shown event handler, add app_ready = True.
In each control event handler where it's needed, add:
If app_ready Then
' code
End If
Starting a routine with something like If initialising Then Exit Sub just doesn't feel right!
Maybe for some functionality you can use the click event instead of the check changed event.
I put a public variable in the Module1 file
Dim Public bolForm_LoadingTF as Boolean = True
In each formLoad event I put
bolForm_LoadingTF = True
In each control with an OnSelectedIndexChanged
event I put if bolForm_LoadingTF = True then Exit Sub
At the end of the form load event I put
bolForm_LoadingTF = False
I am probably breaking a bunch of rules but this works
for me.
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 am new to VB and today I programmed my first form that uses parent and child forms. The assignment asks to "print the active child form" and I am a little stuck. So far this semester printing has not really been a big part of the assignments and I can't seem to find much in the book.
The way the assignment is coded is in the parent form there is a menu strip and I created a print click event in the menu. I guess I'm unsure where to start to make this be able to print just the active child form. My extent of printing my forms has been been dropping a printform from the VB powerpacks and then coding the form to print to preview.
Can someone point me in the right direction? Any hint would be huge so I know at least what to look for in the book. This is for homework.
I found the answer to my own question. Here is a snipped of the code I used. I ended up keeping my printform from the powerpack I just was hung up on how to tell the program to find the active form.
Here is the code I used.
Private Sub PrintToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PrintToolStripMenuItem.Click, PrintToolStripButton.Click
If Me.ActiveMdiChild Is Nothing Then
Return
End If
PrintForm1.Form = Me.ActiveMdiChild
PrintForm1.PrintAction = Printing.PrintAction.PrintToPreview
PrintForm1.Print()
End Sub