CODEWITHSUNDEEP
vb.net
jpavlov
jpavlov

Reputation: 2261

Validation of Decimal in text Box

I am trying to validate wether a number is a decimal in Visual Basic. The results I get when the number is valid the msgBox shows. When it is not valid, I don't receive the msgBox and the program crashes with an error message that number has to be less than infinity.

I tried adding another If Not IsNumeric(txt1.text) then -- But received the same results.

Where did i go wrong?

If IsNumeric(txt1.text) Then
  msgBox("good")
Else
  msgBox("not good")
End If

Upvotes: 2

Views: 22864

Answers (4)

user2219334
user2219334

Reputation: 1

You can also use Textbox Keypress event. i.e 

Private Sub Textbox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles Textbox1.KeyPress
    If (e.KeyChar < "0" Or e.KeyChar > "9") And e.KeyChar <> "." And e.KeyChar <> ControlChars.Back Then
        e.Handled = True
    Else
        If e.KeyChar = "." Then
            If Textbox1.Text.Contains(".") Then
                Beep()
                e.Handled = True
            End If
        End If
    End If

End Sub

I hope this helps.

Upvotes: 0

chillysapien
chillysapien

Reputation: 2316

I have just had to write a function which restricts input to a text box to valid decimal values, and I came up with the following:

 Private Sub validateDecimalTextBox(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) handles myTextBox.keyPress
        Dim textBox As TextBox = DirectCast(sender, TextBox)
        If Not (Char.IsDigit(e.KeyChar) Or Char.IsControl(e.KeyChar) Or (e.KeyChar = "." And textBox.Text.IndexOf(".") < 0) Or (e.KeyChar = "-" And textBox.Text.Length = 0)) Then
            e.Handled = True
        End If
    End Sub

This should restrict user input to decimal values, allowing negative values as well.

If you restrict the user inputs then when you get the value out from the text box you can be more confident that it is valid.

This solution is not complete however as it would allow a user to enter just "-" in the text box which would (presumably) not be a valid input for you. Therefore you can use the solutions that others have mentioned and use any of the following in a sensible way.

double.parse, 
double.tryparse 
isNumeric()

My personal preference would be for isNumeric() but the choice is really up to you.

Upvotes: 1

ColorEyes
ColorEyes

Reputation: 215

Try using Double.TryParse or Decimal.TryParse instead of IsNumeric.

Dim result as Double = 0.0
if Double.TryParse(txt1.text, result) then
  ' valid entry
else
  ' invalid entry
end if

Upvotes: 8

Beth
Beth

Reputation: 9607

You can ignore characters in the textbox's keypress event, like:

Private Sub txtValue_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtValue.KeyPress
        If Not Char.IsDigit(e.KeyChar) Then
            If Not (e.KeyChar = vbBack) Then
               e.Handled = True
            End If
        End If
End Sub

not sure which version of VB you're using, assuming it's .NET

Upvotes: 0

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