Validation to textbox which allows alphanumaric and underscore "_"

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Hi,

I am trying to validate textbox which allows alphanumaric and underscore "_" by using regularexpressions in following method in WPF.
But it allows all the values. I need any modifications in this code or any alternative method that is available...Please look into this.
Thanks.

C#

private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
{
    if (alphaNumericCheck(e.ToString()))
    {
        e.Handled = true;
    }
    else
        e.Handled = false;
}

private bool alphaNumericCheck(string p)
{
    if (regex.IsMatch(p))
        return true;
    else
        return false;
}

Posted 28-May-10 2:49am

sankar.cs

Updated 28-May-10 3:08am

Sandeep Mewara

v2

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Gregory Gadow 28-May-10 9:28am

I expect that the problem is in the regular expression; it would be helpful to have that.

4 solutions

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GregWyatt · Answer 1 · 2010-05-28T04:19:00

Solution 2

To allow alphanumeric and underscore change your regular expression to [^a-zA-Z_0-9]

Like so:

string expression = "[^a-zA-Z_0-9]";
string sIn = "SomeText 900_009";

sIn = Regex.Replace(sIn, expression, "");

Also, using System.Text.RegularExpressions; needs to be included to use Regex.

The third parameter in the Replace method is the string you wish to replace any characters that don't match your regular expression.

The output of the above code would be SomeText900_009

Posted 28-May-10 4:19am

GregWyatt

Updated 28-May-10 4:20am

v2

Comments

Anıl Yıldız 28-May-10 10:45am

Oh, apperantly i don't know what alphanumeric means! Thanks, i added numbers to my answer as well.

William Winner 28-May-10 11:05am

sorry, didn't see you used replace. changed my vote...

GregWyatt 28-May-10 11:17am

Actually it tests all of the characters in the string and replaces any that don't fit the expression with the third parameter. When using Regex.Replace(string input, string expression, string replacewith)

GregWyatt 28-May-10 11:23am

cool Thanks William Winner!

Alan N · Answer 2 · 2010-05-28T05:00:00

Solution 3

sankar.cs wrote:
if (alphaNumericCheck(e.ToString()))

Surely e.ToString() will be "System.Windows.Controls.TextChangedEventArgs"

Alan.

Posted 28-May-10 5:00am

Alan N

Anıl Yıldız · Answer 3 · 2010-05-28T04:16:00

Solution 1

Hello, like the comment above stated, it should be a problem with your Regex which you did not provide. Give this a try and let me know.

C#

private bool alphaNumericCheck(string p)
{
    return new Regex("^[A-Za-z_0-9]").IsMatch(p);
}

Edit: Apperantly forgot about numbers + minor changes.

Thank you,
Anıl Yıldız.

Posted 28-May-10 4:16am

Anıl Yıldız

Updated 28-May-10 4:43am

v5

Comments

William Winner 28-May-10 11:04am

Reason for my vote of 3
close but you're only actually checking the first character with that pattern

William Winner · Answer 4 · 2010-05-28T05:03:00

~~the other two are close, but they didn't actually check their regular expression~~. One of the other answers is close.

What ~~they~~ one of them gave you will only check the first character.

The pattern that you really need is

C#

return new RegEx("^[a-zA-z_0-9]*$");

The caret (^) says check starting at the beginning.

The brackets indicate what is available as a character.

The asterisk (*) says check for 0 or more values.

The $ says that they also have to be at the end as well.

This will ensure that the whole string matches those character choices, not just the first character.

And as one of the others said, you can't just pass in e.ToString(). That's never going to give you what you expect.

Really, from what you're doing, it looks like you may want to handle the keypress event instead.

Using the KeyPress, you could check the e.KeyChar against the regular expression and then decide whether it was handled or not.

Validation to textbox which allows alphanumaric and underscore "_"

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