I'm having a very strange problem in a VB application. I have a function written like this:
In the innermost condition, two statements are commented out here. These were found to have no effect on the strange behaviour. This is the minimal example I've found causing trouble.
(Note that the names of objects have been changed in this example.)
Private Sub MyForm_CellValidating(ByVal sender As Object, ByVal e As DataGridViewCellValidatingEventArgs) Handles myDGV.CellValidating
Dim dgv As DataGridView = CType(sender, DataGridView)
Select Case dgv.Columns(e.ColumnIndex).Name
Case "uniqueColumn"
' Validate that the values in our unique column are unique.
For i As Integer = 0 To dgv.RowCount - 1
If i <> e.RowIndex Then
' Here i != j, so compare to the value...
If e.FormattedValue = dgv.Rows(i).Cells(e.ColumnIndex).FormattedValue Then
e.Cancel = True
'dgv.ShowRowErrors = True
'dgv.Rows(e.RowIndex).ErrorText = "Data in the unique column must be unique"
End If
End If
Next 'i
Case Else
' Perform no validation.
End Select
End Sub
What trouble, you ask? For some inexplicable reason, whenever the line
e.Cancel = True
is executed, afterwards, nearly all buttons and form widgets in the entire application, including even the close button in its window bar (what a user would use to exit the application) stop doing whatever they previously did and now call this event handler instead.
In other words, commenting out that line (and doing the validation manually when the form is submitted) fixes the problems. I'd like to know why this happens, though. Some pointers:
Here's a list of which things are not affected:
The minimize and maximize button in the top bar.
All objects in its menu bar.
This handler is private to its form class, it's not referenced anywhere else in the application.
I'm at a loss. Just how? What could possibly cause this?
e.Cancel is for stopping the validation when the input is deemed incorrect. This causes the cell to still have focus as the user is expected to correct whatever they did wrong. The CellValidating event will then be raised again whenever the cell is about to lose focus until your code deems the input to be correct.
You can use the Control.CausesValidation property to control whether a control (for instance a button) should raise validation events when it gains focus.
I am doing a database validation on the TextBox validating event. I am also using the e.Cancel = True if the data is invalid. The problem is that the validating event is triggered twice ultimately causing the SQL also to run twice, and I don't want that to happen (coz sometime the query is resource intensive).
Steps:
Drag & drop a RadTextBox & a RadLabel to the Form.
For the RadTextBox validating event use the below code.
Run the application, focus the RadTextBox & then click on the label. Then if you check the output window of visual studio you will notice that the console has logged that the validating event was actually triggered twice. (The event runs twice only when I try to click a RadButton or a RadLabel)
I noticed this bug when I was checking my queries in SQL Server Profiler & the query gets executed twice, which is unnecessary. I also checked with actual wincontrols & this issue doesn't exist in them.
How do I fix this issue ?
Here a sample code to replicate the behavior
Private Sub RadTextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles RadTextBox1.Validating
Console.WriteLine("VALIDATING EVENT TRIGGERED")
e.Cancel = True
End Sub
It seems as a known issue with RadTextBox: issue link
Perhaps you can try RadTextBoxControl for your needs?
I have a DataGridView on one of my forms that the user can edit and then update so changes are made to the database it is linked to. For this reason i do not want any of the cells to be left blank. Currently i am using this code:
If datagrdSnippets.Item(e.ColumnIndex, e.RowIndex).Value Is Nothing Then
' Show the user a message
MsgBox("Please ensure the cell has been given a value")
' Fail validation (prevent them from leaving the cell)
e.Cancel = True
End If
In the cell validating property of the DSG, however when i edit a cell and leave it blank nothing happens. Is there something wrong in my code or do i need to use another method?
Please Note: This is in VB.NET and i am currently using the CellValidating event.
Thanks :)
Value is not the property to be checked in the CellValidating Event, but e.FormattedValue. The Value property you are using in your code does not reflect the current cell value, but the last validated one. Sample code:
Private Sub datagrdSnippets_CellValidating(sender As System.Object, e As System.Windows.Forms.DataGridViewCellValidatingEventArgs) Handles datagrdSnippets.CellValidating
If (e.FormattedValue = "Value I want to avoid") Then e.Cancel = True
End Sub
Note that this event is called more than just when the user inputs a value and thus a MsgBox "without any restriction" shouldn't be put here (you have to set something (boolean flags, for example) making sure that the user is the one provoking this method to be called).
My program is already working fine, I use a TextBox to capture the barcode scanner input. The purpose of my program is for time and attendance monitoring, the problem is I want to prevent users from using the keyboard to type in their ID's as it would render the barcode scanner and their ID's with barcodes useless.
*I already tried removing the keyboard from the computer and it did work, but the keyboard must not be removed as a requirement...
Option 1:
Get a barcode-scanner that is connected to a serial-port (raw serial device read by a COM port). As most barcode-scanners emulate keyboard strokes there is no way to directly distinguish a barcode scanner input from a keyboard input (see next option) without going low-level (see last update).
One connected to a serial port (or emulated one via USB as serial-ports are not so common anymore) gives you full control on where the input comes from.
Option 2:
Count number of chars typed by time. Barcode-scanners inject a sequence (line) pretty fast compared to typing. Measuring the time used in the textbox by counting key-presses (use CR+LF as a measure point as these are sent by the scanner as well) can give you one method to distinguish if a human is typing (unless there is one typing fast as f) or the content was injected. If timed-out just reject/clear the input.
In addition the checksum of the barcode (if you use one that contains that) can be used to do an extra validation in addition to time measurement.
(you can detect pasting by overriding the ctrl + v as in the next option).
Option 3:
Combine option 2 but instead of measure in the textbox tap into the ProcessCmdKey() function (by overriding it) and measure there if textbox has focus. This way you can first buffer input, measure time and if within a set time-out value, inject the line into the textbox.
Update:
Option 4: a non-technical approach -
Usability improvements: make it visually very clear that bar-codes must be entered with a scanner and not typed. I am including as an option as it is simple and if made correct also effective (there's no right answer of what is correct unfortunately).
Approached could include f.ex. a watermark in the textbox ("Don't type, scan!" or something in that order). Give it a different color, border, size etc. to distinguish it from normal textboxes, and have a help text associated and available at all time that improves clarity.
I had the same issue and I did the following:
I set an int variable digitsPrevTyped = 0
In the "TextChanged" event of my textbox I added this (the textbox has a maxsize of 17 chars):
Private Sub tbxScannedText_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles tbxScannedText.TextChanged
If tbxScannedText.Text.Length >= 17 Then
SearchFunction(False)
Else
digitsPrevTyped = tbxScannedText.Text.Length
End If
End Sub
Then in my "SearchFunction" I check the following:
Dim inputMethod As Char
If tbxScannedText.TextLength = 17 And digitsPrevTyped = 0 Then
inputMethod = TEXT_SCANNED
Else
inputMethod = TEXT_MANUALLY_ENTERED
End If
If the textbox initially had a length of 0 chars and now has a length of 17 chars it means that the text was scanned. If the length of the previously typed text is less than 17 chars, then the text was typed.
It is very basic but it works for me.
The other possible workaround is to handle keypress event to restrict user input. Do not allow direct input from keyboard and leave the readonly false.
Set following in KeyPress event handler
Private Sub Textbox1_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Textbox1.KeyPress
e.Handled = True
End Sub
Just disable the keyboard anyway.. when using barcode you can disable the keyboard without using readonly on the textbox..
on keypress event put some code i.e
if e.keychar <> chrw(0) then
e.keychar = chrw(0)
end if
that condition will automatically be trigged when user type anything.. you will forcibly disable any input from user but not from barcode
why not use an "alias" in the bar code like "123##$!" (but make it stupid long) is "JSMITH" and set the font color to the same as the background color in the textbox. The user can't see what they're typing or what the bar code value is when it's scanned.
Super simplistic approach that doesn't really require anything added aside from another field in the the user table.
This is an old post, but it took me some time to figure out a relatively clean way to use a barcode scanner and combobox so this is for future users.
Barcode scanners can often be configured to append carriage return and line feed to the end of the scan. I have a form that can take user input or barcode scanner input into a bound combobox using the _PreviewKeyDown property and trapping on the value "Keys.Enter".
Example:
If ((e.KeyCode = Keys.Enter) Then
'do stuff
Else
'do other stuff
End if
Verifying the data exists in the datasource is a bit trickier because the SelectedValue property of the combobox doesn't update so that event doesn't fire. I used a custom method to verify that the value scanned exists in the datasource. This method uses the .Text property of the combo box. It uses:
Me.combobox.findexactstring(Me.combobox.Text)
If e.KeyCode = Keys.Enter And txt.Text.Length > 0 Then
'To Do
Else
'To Do
End if
All of my scanner input goes into a "hidden" textbox, which then fills the visible ones as needed depending on the input. This, of course, means you need to keep track of where the focus is. Any type of control that can get focus will then make a call in those events to return focus to whatever the "active" textbox is at that time, which is normally the hidden one. For example...
Private Sub buttons_gotFocus(sender As System.Object, e As System.EventArgs) Handles btnPrint.GotFocus, btnInMVPageDown.GotFocus, btnAdv.GotFocus, btnManual.GotFocus, btnResend.GotFocus, dgvInbound.GotFocus, dgvOutbound.GotFocus, TCRole.GotFocus
Try
activeTextbox.Focus()
Catch ex As Exception
'ignore any errors
End Try
End Sub
Most other textboxes are disabled by default, and only enabled under certain conditions. Once that entry is done they are disabled and the hidden one will get focus again. Works like a charm.
There's no need to record previous typed characters.
Here's my solution:
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
If TextBox1.Text.Length >= 17 Then '17 or the number of characters your scanner gets.
MsgBox("scanned")
TextBox1.Clear()
Else
If TextBox1.Text.Length <> 0 Then TextBox1.Clear()
End If
End Sub
This answer will handle any fast typing.
Dim scanner_input As Boolean = False
Dim start_typing As DateTime
Private Sub TextBox_part_number_TextChanged(sender As Object, e As EventArgs) Handles
TextBox_part_number.TextChanged
If (TextBox_part_number.Text.Length = 1) Then
start_typing = DateTime.Now
scanner_input = False
'' MsgBox(start_typing.ToString)
ElseIf (TextBox_part_number.Text.Length > 7) Then
If (calc_typing_time(start_typing) < 500) Then
scanner_input = True
Else
scanner_input = False
End If
End If
End Sub
Function calc_typing_time(time_started As DateTime)
Dim time_finished As DateTime
time_finished = DateTime.Now
Dim duration As TimeSpan = time_finished - time_started
Dim time_diff As String = duration.TotalMilliseconds
Return time_diff
End Function
Most of the scanners has a driver to communicate with (Opos) it has functions to open the scanner port and listen to the scanning , so you take the result and decode it in the background and then display the result in the Textbox... what you need to do it to check your barcode scanner's brand go to it's website and download the driver and its manual.
You should just mark your textbox as readonly.
In VB I am working with Windows forms DatagridView.
So here I am trying to get the feature where after running the application, user should be able to resize the column width(On the Fly).
I have gone through lot of stuff but they only provide static solutions. But what I want to achieve is after the application has started running, then if user wants to customise the column width, what is the option for that?
I'm not sure about being able to do this with the standard .NET DataGridViews, but if you download and use the infragistic controls they allow you to change column widths on the fly as standard.
Unless you set the AllowUserToResizeColumns propery to false, the user should be able to modify them however they want with their mouse, just like a "standard" grid like in Excel.
However, I suspect you're asking how to you preserve that setting, so that next time they run it, the column(s) are set back to the user's preference?
One way to do that is to handle the ColumnWidthChanged event on the event and store the value in the registry:
Private Sub DataGridView1_ColumnWidthChanged(sender As Object, e As System.Windows.Forms.DataGridViewColumnEventArgs) Handles data1.ColumnWidthChanged
Dim dt As DataGridView
dt = DirectCast(sender, DataGridView)
With My.Computer.Registry
.CurrentUser.CreateSubKey(csRegKey & "\Columns\" & dt.Name)
.SetValue("HKEY_CURRENT_USER\" & csRegKey & "\Columns\" & dt.Name, e.Column.Name, e.Column.Width, Microsoft.Win32.RegistryValueKind.DWord)
End With
End Sub
Where csRegKey is a constant string value of your choice defining where in the HKCU hive to store the value, eg "Software\MyAppName".
Then, when your app starts up, read the registry for those values and apply them accordingly to the column widths:
Dim key As Microsoft.Win32.RegistryKey
key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(csRegKey & "\Columns\YourDataName")
If key IsNot Nothing Then
For Each colAny As DataGridViewColumn In Me.data1.Columns
If key.GetValue(colAny.Name) <> 0 Then
colAny.Width = key.GetValue(colAny.Name)
End If
Next
key.Close()
End If