Some special characters are not restricted using Regex in KeyDown event in WPF

Question

I'm trying to restrict all characters other than English alphabets, but I'm still able to enter some naughty characters which is not good! How can I prevent that. These naughty characters not caught by my regex are - _ + = ? < > '.

private void AlphaOnlyTextBox_OnKeyDown(object sender, KeyEventArgs e)
{    
    var restrictedChars = new Regex(@"[^a-zA-Z\s]");

    var match = restrictedChars.Match(e.Key.ToString());

    // Check for a naughty character in the KeyDown event.
    if (match.Success)
    {
        // Stop the character from being entered into the control since it is illegal.
        e.Handled = true;
    }
}

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>

        <TextBox Height="21"
                 Width="77" 
                 MaxLength="2"
                 KeyDown="AlphaOnlyTextBox_OnKeyDown"
                                           >
        </TextBox>
    </Grid>
</Window>

The regex seems to catch those (as tested on regexr.com). Are you sure the problem isn't elsewhere? — rtmh
– rtmh, Commented Jul 11, 2016 at 18:04
@rtmh You can build the question easily in WPF/C#. It doesn't work for some odd reason! — Vahid
– Vahid, Commented Jul 11, 2016 at 18:07
@rtmh One suggestion! Maybe it has something to do with pressing the Shift button! Because we need to press that to enter +? — Vahid
– Vahid, Commented Jul 11, 2016 at 18:11
I wouldn't say we can build it easily. As for that issue, look into the specifics of the KeyEventArgs::Key functions, does it return what you expect? — rtmh
– rtmh, Commented Jul 11, 2016 at 18:13

Itay Podhajcer · Accepted Answer · 2016-07-11 18:35:34Z

2

Try this expression:

var restrictedChars = new Regex(@"[^(\W_0-9)]+");

It will exclude everything but large and small letter characters (not depending on a spceific language).

Hope it helps!

answered Jul 11, 2016 at 18:35

Itay Podhajcer

2,6642 gold badges11 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Vahid Over a year ago

Thanks but it excludes everything! Even the normal alphabets!

Itay Podhajcer Over a year ago

Make sure you are using an upper case 'W' in the expression, because a lower case 'w' might cause the problem you have with the expression in my answer.

Vahid Over a year ago

Thanks Italy, it seems the problem is somewhere else, see the answer below.

Vahid · Accepted Answer · 2016-07-11 19:03:06Z

2

After so much head-scratching I realized that for some reasons unknown to me, KeyDown event doesn't capture certain characters, but PreviewTextInput does!

    private void UIElement_OnPreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        var restrictedChars = new Regex(@"[^a-zA-Z\s]");

        var match = restrictedChars.Match(e.Text);

        // Check for a naughty character in the KeyDown event.
        if (match.Success)
        {
            // Stop the character from being entered into the control since it is illegal.
            e.Handled = true;
        }
    }

    <TextBox Height="21"
             Width="77" 
             MaxLength="2"
             PreviewTextInput="UIElement_OnPreviewTextInput"
                                       >
    </TextBox>

If you also want to disable Space button:

    <TextBox Height="21"
             Width="77" 
             MaxLength="2"
             PreviewTextInput="UIElement_OnPreviewTextInput"
             PreviewKeyDown="UIElement_OnKeyDown"
                                       >
    </TextBox>

    private void UIElement_OnKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Space)
        {
            e.Handled = true;
        }
    }

edited Jul 11, 2016 at 19:03

answered Jul 11, 2016 at 18:50

Vahid

5,51415 gold badges84 silver badges161 bronze badges

1 Comment

rtmh Over a year ago

I knew there must have been something better, Good find. :)

Collectives™ on Stack Overflow

Some special characters are not restricted using Regex in KeyDown event in WPF

2 Answers 2

3 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related