Blog : Letter to be accepted into the textbox on vb.net
letter to be accepted into the textbox on vb.net
Ive been trying to do this, so the textbox only accepts letters, but the validation does not work. Even when I enter numbers it processes it and shows the first lblError of "Thankyou for your details", where it should actually be "Enter A Valid Name ". is their are validation test similar to IsNumeric for this type of problem? plz help
Dim MyName As String
If txtMyName.Text Then
MyName = txtMyName.Text
lblError.Text = "Thankyou for your details"
Else
lblError.Text = "Enter A Valid Name "
End If
End Sub
End Class
And I need simple methods, nothing with [a-zA-Z0-9], or RegEx patterns, as ive researched these and I cannot use them.
Thankyou
This looks like a homework assignment. Are you looking for a way to stop the user entering them, if so look at events. If you want to validate it after they have entered one way could be to check each
The basics are that to match a strinh of letters a regex is the best way. I dont know of any isStringLetters built in. The reason we are all saying regex is because it is the best way we know (plus the least lines of code – Chris Jan 5 '13 at 9:01
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3 Answers active oldest votes up vote
2
down vote You can check the text string, i.e., textbox1.text, to make sure it has nothing besides alphabet characters in the .Leave event. This will catch an error when the user tabs to the next control, for example. You can do this using a regular expression (import System.Text.RegularExpressions for this example), or you can check the text "manually."
Private Sub TextBox1_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.Leave
If Not Regex.Match(TextBox1.Text, "^[a-z]*$", RegexOptions.IgnoreCase).Success Then
MsgBox("Please enter alpha text only.")
TextBox1.Focus()
End If
End Sub
If you want to stop the user as soon as a non-alpha key is pressed, you can use the TextChanged event instead of the .Leave event.
You can build a array of all english letters like this (it's uppercase) then you can check if all characters in the name is in the array.
Private Shared Function IsLetters(s As String) As Boolean
For Each c As Char In s.ToUpper().ToCharArray()
If Not onlyLetters().Contains(c) Then
Return False
End If
Next
Return True
End Function
Private Shared Function onlyLetters() As Char()
Dim strs = New List(Of Char)()
Dim o As Char = "A"C
For i As Integer = 0 To 25
strs.Add(Convert.ToChar(o + i))
Next
Return strs.ToArray()
End Function
This works by removing all upper and lowercase letters from a string - leaving behind anything else. If we then see how long stringname.length the string is after the removal has completed, and find the number is zero then the validation has passed. However if the number is greater than zero, then our string contained non alphabet characters.
If (TextBox1.Text <> "") Then
Dim userInput As String = TextBox1.Text
Dim filteredUserInput As String = userInput
Dim listOfLetters As String() = New String() {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "a", "b", "c", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"}
' go through each letter in the 'listOfLetters' array and replace that letter with.. nothing
For Each letter In listOfLetters
filteredUserInput = Replace(filteredUserInput, letter, "")
Next
' now we have done the work - count how many characters are left in the string, if it is more than 0 we have invalid characters
If (filteredUserInput <> "") Then
MsgBox("This failed validation, contains invalid chars (" + Str(filteredUserInput.Length) + ")")
Else
MsgBox("This passed validation")
End If
End If
Or if you want it function-ified..
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If (TextBox1.Text <> "") Then
Dim userInput As String = TextBox1.Text
' if the 'isThisAValidString()' returns true then it is a valid (and has not faild validation) a-zA-Z
If (isThisAValidString(userInput) = True) Then
MsgBox("This is valid")
Else
MsgBox("This is not valid")
End If
End If
End Sub
Function isThisAValidString(input As String)
Dim userInput As String = input
Dim filteredUserInput As String = userInput
Dim listOfLetters As String() = New String() {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "a", "b", "c", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"}
' go through each letter in the 'listOfLetters' array and replace that letter with.. nothing
For Each letter In listOfLetters
filteredUserInput = Replace(filteredUserInput, letter, "")
Next
' now we have done the work - count how many characters are left in the string, if it is more than 0 we have invalid characters
If (filteredUserInput <> "") Then
' this failed!
Return False
Else
'this passed
Return True
End If
End Function
