I took an entry level computer programming class this past term and I'm having problems with my final project. I have to design a program in visual basic GUI that asks the player to accurately guess a number between 1-100 within a limited number of guesses.
My first form asks the user to set the number of guesses allowed. It has one textbox and an "enter" button, among other buttons that I've gotten to work.
I'm trying to get code to work that will validate the input on the guesses allowed. Specifically, I want a message box to pop up if the player enters letters or special characters instead of numbers, or enters a number less than zero, or greater than twenty. Here's what I have:
Public Class Noofguesses
Shared maxguesscnt As Integer
Private Sub Numberofguesses_TextChanged(sender As Object, e As EventArgs) Handles Numberofguesses.TextChanged
End Sub
Private Sub Quit_Click(sender As Object, e As EventArgs) Handles Quit.Click
End
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Form3.Show()
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If Val(Numberofguesses) > 20 Then MsgBox("Number of Guesses Cannot Exceed 20")
If Val(Numberofguesses) < 0 Then MsgBox("Number of Guesses Must Be Greater Than 0")
If Not IsNumeric(Numberofguesses) Then MsgBox("Entry Cannot be Letters or Characters")
Me.Close()
Form2.Show()
End Sub
End Class
What am I doing wrong? Please let me know.
Thanks
I would generally suggest using a NumericUpDown rather than a TextBox, in which case no validation is required. As this is an assignment though, I'm guessing that validating a TextBox is a requirement. In that case, you should use Integer.TryParse to validate a String, i.e. the Text of the TextBox and convert it if it is valid. You can then test the converted value to make sure that it isn't less than zero, etc. I'm not going to write the code for you, given that this is homework, but that should be enough for you to do it yourself or, if you feel you must, find examples online.
I've made a program in VB where the user selects from a drop down box whether they would like to find out speed, distance or time. There are three textboxes on the form where the user can enter speed, distance and time, and they don't enter anything for the one which they want to find out.
When the user chooses to find out speed, I want the speed textbox to be changed to read only, when the user chooses to find out distance, I want that textbox to be changed to read only, etc.
Thanks in advance.
You can make a Textbox read only by using the following code:
textbox1.ReadOnly = true
You can also found out more here.
Handle the SelectedIndexChanged event and set the Enabled property in there.
Private Sub ComboBox1_SelectedIndexChanged(sender As System.Object, e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
Me.TextBoxSpeed.Enabled = ComboBox1.SelectedItem <> "Speed"
Me.TextBoxTime.Enabled = ComboBox1.SelectedItem <> "Time"
Me.TextBoxDistance.Enabled = ComboBox1.SelectedItem <> "Distance"
End Sub
I have a TextBox by which if the user enters more than 10 characters it displays a MsgBox. That part works :D
The problem is the message also displays if the TextBox is empty and the user types the first character. I think thats because Null is seen as something greater than 10? but I'm not sure.
A) What is going on?
B) How can I fix this?
Private Sub TextBox3_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox3.KeyPress
If TextBox3.Text.Length >= 10 Then
MsgBox("WARNING")
End If
End Sub
You can try this. By using trim, white space characters is ignored. For an example, if the user only entered 10 [Spacebar] keys it will trim it out.
Private Sub TextBox3_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox3.KeyPress
If TextBox3.Text.Trim().Length() >= 10 Then
MsgBox("WARNING")
End If
End Sub
I am a simple beginner and need small help:
I have textbox1 and textbox2.
Supposed when you put a number (for ex. 21) in the textbox1, I need textbox2 to give me the double number (42). I mean that I need textbox2.text=2*textbox1.text
I used this simple code :
Private Sub TextBox1_Textlength(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles TextBox1.TextChanged
TextBox2.Text = 2*TextBox1.Text
The problem is: when I wrote (in textbo1) only one digit everything it's ok, but I could not write two (or more) digits.
How do I make a delay (interval) which allows me to type a number like (1990 for example) before firing textbox1_changed?
TextChanged fires every time you change the content of the textbox. So there is no way to block this behavior. Perhaps you could add a button and move the recalculation on the button click event or better add an event handler for the Validating event.
This event is triggered when you exit from the control and you have also the option to check the input and block the exiting from the TextBox control
Private Sub textBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
Dim v as Integer
if Not Int32.TryParse(TextBox1.Text, v) Then
e.Cancel = True
MessageBox.Show("Please type a valid number")
Else
TextBox2.Text = (v * 2).ToString
End If
End Sub
Notice that when you handle the user input expecting a numeric value you should apply particular attention because you don't know what the user types. In this case the Int32.TryParse seems to be the appropriate approach.
Another suggestion is to enable immediately the Option Strict ON in your project, the default is OFF and this allows very dangerous code like treating a string like it was a number.
You don't need to. Just allow the TextChanged event to fire every time, and the second text box will always display twice the value of the first one, so when 1 is entered, it will show 2, when the 9 is added, it will show 38, and so on. You should of course address Steve's concerns about validation, and implied type conversions.
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.