IsNumeric Function in vb.net

It behaves like TryParse, which accepts optional leading
or trailing whitespace. See the Remarks here:

https://learn.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=net-5.0

• Wayne

Here are a couple ideas

• Use a custom TextBox (note IsNumeric assertions)
• For a regular TextBox use either TextChanged or KeyPress events

The following are basics that can be expanded on

Public Class Form1  
    Private Sub IsNumberButton_Click(sender As Object, e As EventArgs) Handles IsNumberButton.Click  
  
        If SpecialTextBox1.IsNumeric Then  
            MessageBox.Show("Numeric")  
        Else  
            MessageBox.Show("Not numeric")  
        End If  
  
    End Sub  
    ''' <summary>  
    ''' Integer, Decimal, Double  
    ''' </summary>  
    ''' <param name="sender"></param>  
    ''' <param name="e"></param>  
    Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress  
  
        If Not Char.IsControl(e.KeyChar) AndAlso Not Char.IsDigit(e.KeyChar) AndAlso (e.KeyChar <> "."c) Then  
            e.Handled = True  
        End If  
  
        If (e.KeyChar = "."c) AndAlso ((TryCast(sender, TextBox)).Text.IndexOf("."c) > -1) Then  
            e.Handled = True  
        End If  
  
    End Sub  
    ''' <summary>  
    ''' Integer only  
    ''' </summary>  
    ''' <param name="sender"></param>  
    ''' <param name="e"></param>  
    Private Sub TextBox2_TextChanged(sender As Object, e As EventArgs) Handles TextBox2.TextChanged  
          
        Dim textBox = ctype(sender, TextBox)  
  
        If System.Text.RegularExpressions.Regex.IsMatch(TextBox.Text, "[^0-9]") Then  
            TextBox.Text = TextBox2.Text.Remove(TextBox.Text.Length - 1)  
        End If  
  
    End Sub  
End Class  
  
Public Class SpecialTextBox  
    Inherits TextBox  
  
    ''' <summary>  
    ''' Determine if we are dealing with a number  
    ''' </summary>  
    ''' <returns></returns>  
    Public ReadOnly Property IsNumeric() As Boolean  
        Get  
            If Double.TryParse(Text.Replace(" "c, "").Trim(), Nothing) Then  
                Return True  
            Else  
                Return False  
            End If  
        End Get  
    End Property  
  
End Class  

It seems to also return True in these cases: "&HAC", "&o0", "5.2", "5,2", "5+". Maybe it is better to use TryParse in your case, where you can specify more parameters and even the language (culture)? Sometimes you can also use Regular Expressions.

Hi @Babak Boloury ,
You can remove all spaces when using 'IsNumeric'.
For example:

        If Not IsNumeric(TextBox1.Text.Replace(" ", "")) Then  
            MsgBox("Please enter a numeric value.", MsgBoxStyle.Critical, My.Application.Info.ProductName & " Error")  
            TextBox1.SelectAll()  
            TextBox1.Focus()  
        End If  

Best Regards,
Xingyu Zhao
*
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