How to validate a textbox ?

Deepak M

6y1kWindows Forms

How to validate a textbox to accept only numbers, negative numbers and one point value in win app ?

10 Replies

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Amit Mohanty6y ago
Accepted answer
Hey try the below code.
private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    // allow only numbers
    if (e.KeyChar >= 48 && e.KeyChar <= 57 || e.KeyChar == 46 || e.KeyChar == 45)
    {
        e.Handled = false;
    }
    else
    {
        e.Handled = true;
    }

    // only allow one decimal point
    if (e.KeyChar == 46 && (sender as TextBox).Text.IndexOf('.') > -1)
    {
        e.Handled = true;
    }

    // allow negative
    Regex reg = new Regex(@"^-?\d+[.]?\d*$");
    if (!reg.IsMatch((sender as TextBox).Text.Insert((sender as TextBox).SelectionStart, e.KeyChar.ToString()) + "1"))
    {
        e.Handled = true;
    }

    // allow backspace
    if (e.KeyChar == 8)
    {
        e.Handled = false;
    }
}
+1
Deepak M6y ago
Hii Piyush sir the below code accepts nothing.
string temp = (sender as TextBox).Text;
if (!char.IsControl(e.KeyChar) && !Regex.IsMatch(temp, @"/^(?!-0(\.0+)?$)-?(0|[1-9]\d*)(\.\d+)?$/") && !(e.KeyChar == (char)Keys.Back))
{
    e.Handled = true;
}
0
Piyush Pansuriya6y ago
Hi Kartik,
This is the simple code you can try. Your previous code may allow the paste somthing.
private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
{
    string temp = (sender as TextBox).Text;
    if (!char.IsControl(e.KeyChar) && !Regex.IsMatch(temp, @"/^(?!-0(\.0+)?$)-?(0|[1-9]\d*)(\.\d+)?$/") && !(e.KeyChar == (char)Keys.Back))
    {
        e.Handled = true;
    }
}
-1
Deepak M6y ago
Thank you Amit sir it's working.
0
Deepak M6y ago
Thank you for replying Piyush Pansuriya sir but it will accept "-" symbol between numbers and also accepting more than one ".".
0
Piyush Pansuriya6y ago
That is the same thing which I suggest.
But As per your requirement If you need numeric textbox, than you have to create custom control and you can reuse it any where.
Below link will helps you to create custome control for numeric textbox.

https://www.c-sharpcorner.com/uploadfile/sapnabeniwal/numeric-textbox-custom-control/

or if you need to add negative number and decimal place into that than use below code.
private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
{
    char decimalSeparator = Convert.ToChar(CultureInfo.CurrentCulture. NumberFormat.NumberDecimalSeparator);

    char negativeSign = Convert.ToChar(CultureInfo.CurrentCulture.NumberFormat.NegativeSign);

    if(!(Char.IsDigit(e.KeyChar) || (e.KeyChar == (char)Keys.Back) || (e.KeyChar == decimalSeparator) || (e.KeyChar == negativeSign)))
          e.Handled = true;
}
0
Deepak M6y ago
Hii Piyush Pansuriya & Jignesh Kumar below codes are only accepted the numeric value. my requirement is textbox to accept only numbers, negative numbers, and one point value.
0
Jignesh Kumar6y ago
Hello,

Please find below link which will help you.
https://www.c-sharpcorner.com/blogs/how-to-create-a-textbox-accepting-only-numbers-in-windows-forms1
0
Piyush Pansuriya6y ago
Hi,
on keypress event put this code.
private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
{
     if (!(Char.IsDigit(e.KeyChar) || (e.KeyChar == (char)Keys.Back)))
          e.Handled = true;
}
0
Amit Gupta6y ago
Do take advantage of Google by searching Accept numeric values only in c#, you will get plenty of techniques
-1