如何验证Vb中的文本框仅允许3个数字和2个字母？

Question

I figured out how too get only numbers in a text box with is code:

 Dim smessage As String = String.Empty

 If Not IsNumeric(Student_IDTextBox.Text) Then
      smessage += "The ID must be Numeric!" + Environment.NewLine
 End If

But I would like this textbox to have 2 letters and 3 numbers, do you know what the best way to programme this in vb?

Answer 1

please try masked textbox with custom mask. set mask like- LLL00. refer this link http://msdn.microsoft.com/en-us/library/system.windows.forms.maskedtextbox.mask.aspx

Answer 2

If the ID must be 3 numerals and 2 characters than there is probably also a pattern to it (as with many license plates) and more important than the mere character type count. A masked text box is one way, counting the numerals and counting the letters is another.

If there is a pattern such as AAA-NN or AAANN, you could split the ID into 2 inputs one alpha, one numeric. This is often done with IDs in patterns such as a (US) social security number (NNN-NN-NNNN). RegEx could also probably be used to test the pattern.

If this is a login or otherwise a database app, rather than write too much code to simply test the pattern test the entry. You could collect whatever they type and do a simple query to see if the ID exists, which after all is far more important than the pattern.

A label on the form can tell them to use ###AA or whatever, but it seems silly to test the pattern and report a pattern error when you can simply tell them when it is invalid. After all, even if it has the correct pattern, it can still be an invalid ID.

Answer 3

This is certainly not the best way, but I do not know if you will ever find the best way because best is subjective and often dependent on more than one situation as well as opinion.

Assuming a text box with the name txtinput and a label where you will be displaying the results named lblMessage and assuming you are using ASCII character input:

In the TextChanged event of txtinput you could have the following:

'Check if the length is greater than five, if it is truncate it.
If txtinput.Text.Length > 5 Then
    txtinput.Text = Mid(txtinput.Text, 1, 5)
    txtinput.Select(txtinput.Text.Length, 0)
End If

'counters for letters and numbers
Dim letters As Integer = 0
Dim numbers As Integer = 0

'Parse and compare the input
For Each c As Char In txtinput.Text
    If Asc(c) >= 48 And Asc(c) <= 57 Then 'ASCII characters for 0-9
        numbers += 1
    ElseIf Asc(c) >= 65 And Asc(c) <= 90 Then 'ASCII characters for A-Z
        letters += 1
    ElseIf Asc(c) >= 97 And Asc(c) <= 122 Then 'ASCII characters for a-z
        letters += 1
    End If
Next

If letters = 2 And numbers = 3 Then
    lblMessage.Text = "Correct Format"
Else
    lblMessage.Text = "Incorrect Format"
End If

Using Linq:

If txtinput.Text.Length > 5 Then
    txtinput.Text = Mid(txtinput.Text, 1, 5)
    txtinput.Select(txtinput.Text.Length, 0)
End If

If txtinput.Text.Count(Function(x As Char) Char.IsLetter(x)) = 3 And txtinput.Text.Count(Function(x As Char) Char.IsNumber(x)) = 2 Then
    lblMessage.Text = "Correct Format"
Else
    lblMessage.Text = "Incorrect Format"
End If