How to validate only number in winform?

Question

How to validate for numbers without using keypress option why isnt Char.IsNumber or .IsDigit working or should I use regex expression for validation

private bool ValidateContact()
{
    if (Char.IsNumber(textBox4.Text)){
        return true;
}

because `Char.IsDigit` needs a char not a string – Tim Schmelter Jun 18 '14 at 07:12 — Tim Schmelter, Jun 18 '14 at 07:12
return Int.TryParse(textbox4.Text, out t) – VisualBean Jun 18 '14 at 07:12 — VisualBean, Jun 18 '14 at 07:12

Patrick Hofman · Accepted Answer · 2014-06-18T07:32:18.953

7

You could simply parse the number:

private bool ValidateContact()
{
    int val;
    if (int.TryParse(textBox4.Text, out val))
    {
       return true;
    }
    else
    {
        return false;
    }
}

You are trying to call a method that is written for char for string. You have to do them all separately, or use a method that is much easier to use, like the above code.

edited Jun 18 '14 at 07:32

answered Jun 18 '14 at 07:13

Patrick Hofman

153,850
22
249
325

Your solution will give an error. `Not all code paths return a value` – Ricky Jun 18 '14 at 07:31
But what if user wants to enter an decimal number? – TC Alper Tokcan Jun 18 '14 at 07:37
Then this won't work, try to use `decimal.TryParse` then. The original code from OP doesn't seem to need that, so I left that out. (Contract numbers usually don't have decimals) – Patrick Hofman Jun 18 '14 at 07:38
@skates008: Need more help? – Patrick Hofman Jun 18 '14 at 08:00
@skates008: please don't forget to mark your question answered if it was. – Patrick Hofman Jun 18 '14 at 15:23

score 3 · Answer 2 · edited May 23 '17 at 10:29

3

why isnt Char.IsNumber or .IsDigit working

because Char.IsDigit wants a char not a string. So you could check all characters:

private bool ValidateContact()
{
    return textBox4.Text.All(Char.IsDigit);
}

or - better because IsDigit includes unicode characters - use int.TryParse:

private bool ValidateContact()
{
    int i;
    return int.TryParse(textBox4.Text, out i);
}

edited May 23 '17 at 10:29

Community

1
1

answered Jun 18 '14 at 07:13

Tim Schmelter

450,073
74
686
939

2

I personally don't rely on this solution. `char.IsDigit` returns true for all unicode digits.it seems `int.TryParse` is more appropriate here. – Selman Genç Jun 18 '14 at 07:15
1

@Selman22: good point. I've edited my answer accordingly and included [a link to my own question](http://stackoverflow.com/q/22063436/284240) which was related to this. – Tim Schmelter Jun 18 '14 at 07:19

score 1 · Answer 3 · answered Jun 18 '14 at 07:14

1

Parse the string as:

private bool ValidateContact()
{
    int n;
    return int.TryParse(textbox4.Text, out n);
}

answered Jun 18 '14 at 07:14

Ricky

2,323
6
22
22

score 0 · Answer 4 · edited Jun 18 '14 at 07:14

as documented here http://codepoint.wordpress.com/2011/07/18/numeric-only-text-box-in-net-winforms/ :-

We can create Numeric only text boxes in .Net Windows forms application with adding below code in Key Press Event.

Numeric only text boxes

private void txtBox_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && e.KeyChar != '.')
    {
        e.Handled = true;
    }

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

score 0 · Answer 5 · answered Jun 18 '14 at 07:13

0

You should be using

int n;
bool isNumeric = int.TryParse("123", out n);

Not Char.IsNumber() as that only tests a character.

answered Jun 18 '14 at 07:13

3dd

2,520
13
20

score 0 · Answer 6 · edited May 23 '17 at 11:47

Try supress every key but numeric or decimal point on textbox.KeyPress

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
  if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && e.KeyChar != '.')
  {
    e.Handled = true;
  }

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

Why controlling on keypress ?

Because alerting user after he enters a value is not a efficent way to get input from user. Instead of doing this , you can prevent user from entering non/valid values when user typing.

Based on Matt Hamilton's Ansver on this Question

Question states 'without using keypress option'. – Patrick Hofman Jun 18 '14 at 08:31 — Patrick Hofman, Jun 18 '14 at 08:31

score 0 · Answer 7 · edited May 23 '17 at 12:34

0

You can use regular expression too.

 if (System.Text.RegularExpressions.Regex.IsMatch("[^0-9]", textBox1.Text))
        {
            MessageBox.Show("Please enter only numbers.");
            textBox1.Text.Remove(textBox1.Text.Length - 1);
        }

Also you can check, textbox only allow numeric value :

How do I make a textbox that only accepts numbers?

edited May 23 '17 at 12:34

Community

1
1

answered Jun 18 '14 at 07:18

Ajay2707

5,690
6
40
58

How to validate only number in winform?

7 Answers7

Linked