How to validate a textbox ?

Question

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

Amit Mohanty · Answer

Hey try the below code. private void TextBox1_KeyPress( object sender, KeyPressEventArgs e) { // allow only numbers if (e.KeyChar >= 48 && e.KeyChar { 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 ; } }

Piyush Pansuriya · Answer

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 ; }

Piyush Pansuriya · Answer

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 ; }

Deepak M · Answer

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 ; }

Piyush Pansuriya · Answer

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 ; } }

Deepak M · Answer

Thank you Amit sir it's working.

Deepak M · Answer

Thank you for replying Piyush Pansuriya sir but it will accept " - " symbol between numbers and also accepting more than one " . ".

Deepak M · Answer

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.

Jignesh Kumar · Answer

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

Amit Gupta · Answer

Do take advantage of Google by searching Accept numeric values only in c#, you will get plenty of techniques

How to validate a textbox ?

Answers (10)