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Check if text box input is numeric

I did some research on this and still cannot get my program to work. I just need to check the text box to see if user input is a numeric value or not (except for "." And "/")

My code is still

 Private Sub Num1_KeyPress(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Num1.KeyPress
    Dim UserEntry As Boolean
    If UserEntry = IsNumeric(False) Then
        MessageBox.Show("That not numeric!")
    End If
End Sub
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7 answers

I think you better use the event TextBox.KeyUpit passes KeyEventArgs. Try the following:

Private Sub Num1_KeyUp(sender As System.Object, e As System.Windows.Forms.KeyEventArgs) Handles Num1.KeyUp

    Dim isDigit As Boolean = Char.IsDigit(ChrW(e.KeyValue))
    Dim isKeypadNum As Boolean = e.KeyCode >= Keys.NumPad0 And e.KeyCode <= Keys.NumPad9
    Dim isBackOrSlashOrPeriod As Boolean = (e.KeyCode = Keys.Decimal Or e.KeyCode = Keys.Oem2 Or e.KeyCode = Keys.Back Or e.KeyCode = Keys.OemPeriod)

    If Not (isDigit Or isKeypadNum Or isBackOrSlashOrPeriod) Then
        MessageBox.Show("That not numeric!")
    End If

End Sub
+3
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I recommend handling TextChanged and checking for an integer instead of a single character.

Private Sub Num1_TextChanged(sender As Object, e As TextChangedEventArgs) Handles Num1.TextChanged
        If IsInputNumeric(Num1.Text) Then
            'handle numeric input
        Else
            'handle not a number
        End If
    End Sub

    Private Function IsInputNumeric(input As String) As Boolean
        If String.IsNullOrWhiteSpace(input) Then Return False
        If IsNumeric(input) Then Return True
        Dim parts() As String = input.Split("/"c)
        If parts.Length <> 2 Then Return False
        Return IsNumeric(parts(0)) AndAlso IsNumeric(parts(1))
    End Function
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Public Function onlyNumbers(ByVal KeyChar As Char) As Boolean
    Dim allowedChars As String

    allowedChars = "0123456789./" 

    If allowedChars.IndexOf(KeyChar) = -1 And (Asc(KeyChar)) <> 8 Then 
        Return True
    End If

    Return False
End Function

true char.

:

e.handled = onlyNumbers(e.keychar)
0

, textBox LostFocus eventHandler, , . OK.

a) - "0123456789./" ,

b) , "/" ( ), IsNumeric() . - , .

, 1/2/2,.i.e. 1/4. , , 1 "/".

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Private Sub tbYear_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles tbYear.KeyPress
    If e.KeyChar < Chr(48) Or e.KeyChar > Chr(57) Then
        e.KeyChar = Nothing
    End If
End Sub
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' Validates textboxes for numeric only keystrokes.  Hook this up to the 
' PreviewTextInput of the desired textbox
Private Sub SetTextboxNumericOnly(sender As Object,
                                  e As TextCompositionEventArgs)

    Dim regex As New System.Text.RegularExpressions.Regex("[^0-9]+")
    e.Handled = regex.IsMatch(e.Text)

End Sub

, , , . , .

0

, , , .TryParse, , IsNumeric:

, TryParse , IsNumeric .

The second reason is that you can provide IsNumeric with any object you want (also, for example, Button), and it accepts it. You would never find such errors at compile time. Instead, with TryParse, you can only pass a string as your first parameter.

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