Validation of textbox for decimal numbers

Question

I want to restrict the user to enter decimal number only in format like 1.2,11.22,1.22,11.2 please tell me how to validate input in keypress event?

Ranjit Powar · Answer

Thanks Vulpes for your help. I write got solution for my problem. I write follwing code and it works fine. private void txtCMinFat_KeyPress(object sender, KeyPressEventArgs e) { if (char.IsNumber(e.KeyChar) || e.KeyChar == '.') { int len = txtCMinFat.Text.Length; bool hasDot = txtCMinFat.Text.Contains("."); if (hasDot && e.KeyChar == '.') { e.Handled = true; } if (len >= 2 && !hasDot ) { if (char.IsNumber(e.KeyChar)) { e.Handled = true; } } if (Regex.IsMatch(txtCMinFat.Text, "^\d*\.\d{2}$")) e.Handled = true; } else e.Handled = e.KeyChar != (char)Keys.Back; }

Vulpes · Answer

OK, in that case it's easier to start again: private void txtCMaxFat_KeyPress(object sender, KeyPressEventArgs e) { if (char.IsNumber(e.KeyChar) || e.KeyChar == '.') { int len = txtCMaxFat.Text.Length; int index = txtCMaxFat.Text.IndexOf("."); if (len == 5 || (e.KeyChar == '.' && (len == 0 || len > 2 || index >= 0)) || (e.KeyChar != '.' && index == -1 && len == 2 ) || (e.KeyChar != '.' && index == 1 && len == 4 )) e.Handled = true; } else e.Handled = e.KeyChar != (char)Keys.Back; } However, you'll still need some 'post entry' validation as the KeyPress event can't capture focus leaving the textbox or text being pasted in. If you handle the Leave event as well then this will prevent focus leaving the textbox until valid input is entered: private void txtCMaxFat_Leave(object sender, EventArgs e) { if (!Regex.IsMatch(txtCMaxFat.Text, @"^\d{1,2}\.\d{1,2}$")) { txtCMaxFat.Focus(); txtCMaxFat.Select(txtCMaxFat.Text.Length + 1, 0); } }

Ranjit Powar · Answer

I want to take only two or one digit whole number and two or one digit decimal part

Vulpes · Answer

OK, assuming you'd also want to allow numbers with no decimal point and up to 4 digits precision (such as 1234), try this: private void txtCMaxFat_KeyPress(object sender, KeyPressEventArgs e) { if (char.IsNumber(e.KeyChar) || e.KeyChar == '.') { int len = txtCMaxFat.Text.Length; bool hasDot = txtCMaxFat.Text.Contains("."); if ((len >= 5 && hasDot) || (len >= 4 && !hasDot) || Regex.IsMatch(txtCMaxFat.Text,"^\d*\.\d{2}$")) e.Handled = true; } else e.Handled = e.KeyChar != (char)Keys.Back; }

Ranjit Powar · Answer

I want to take decimal format(4,2).

Vulpes · Answer

@Ranjit, I'm struggling to understand what you're trying to do here because, as you say yourself, the existing code validates decimal numbers up to 2 decimal places and so it already validates them if they only have one decimal place?

Ranjit Powar · Answer

I use follwing code for validation of decimal numbers up to 2 decimal places like 123.33,33.33 4.33 in keypress event of textbox in windows form. And it works fine. private void txtCMaxFat_KeyPress(object sender, KeyPressEventArgs e) { if (char.IsNumber(e.KeyChar) || e.KeyChar == '.') { if (Regex.IsMatch( txtCMaxFat.Text, "^\d*\.\d{2}$")) e.Handled = true; } else e.Handled = e.KeyChar != (char)Keys.Back; } Now I want to change it so that it take number only in format like 1.2,11.22,1.22,11.2

sudipta sanyal · Answer

private void OnNumericKeyPress(object sender, KeyPressEventArgs e) { if (Char.IsControl(e.KeyChar)) { } else if (Char.IsNumber(e.KeyChar) || e.KeyChar == '.') { TextBox tb = sender as TextBox; int cursorPosLeft = tb.SelectionStart; int cursorPosRight = tb.SelectionStart + tb.SelectionLength; string result = tb.Text.Substring(0, cursorPosLeft) + e.KeyChar + tb.Text.Substring(cursorPosRight); string[] parts = result.Split('.'); if (parts.Length > 1) { if (parts[1].Length > 2 || parts.Length > 2) { e.Handled = true; } } } http://social.msdn.microsoft.com/Forums/en-US/46e32025-b060-4809-b9a7-caf1d39de40b/only-allow-2-decimal-places-in-a-textbox?forum=winforms

Ranjit Powar · Answer

Not working it takes only one digit.

sudipta sanyal · Answer

you are not specified where u used this means in aspx page or windows form. i post both FOR ASPX function checkDecimal(el){ var ex = /^[0-9]+\.?[0-2]*$/; if(ex.test(el.value)==false){ alert('Decimal Value upto 2 places allowed !'); el.value = ''; } } FOR windows form var text = textBox1.Text.Trim(); if (Regex.IsMatch(text, @"^\d{1,2}(\.\d{1,2})?$")) { // Do something here } else { MessageBox.Show("Doesn't match pattern"); }

Validation of textbox for decimal numbers

Answers (10)