How do I get a TextBox to only accept numeric input in WPF?

Add a preview text input event. Like so: <TextBox PreviewTextInput="PreviewTextInput" />.

Then inside that set the e.Handled if the text isn't allowed. e.Handled = !IsTextAllowed(e.Text);

I use a simple regex in IsTextAllowed method to see if I should allow what they've typed. In my case I only want to allow numbers, dots and dashes.

private static readonly Regex _regex = new Regex("[^0-9.-]+"); //regex that matches disallowed textprivate static bool IsTextAllowed(string text){    return !_regex.IsMatch(text);}

If you want to prevent pasting of incorrect data hook up the DataObject.Pasting event DataObject.Pasting="TextBoxPasting" as shown here (code excerpted):

// Use the DataObject.Pasting Handler private void TextBoxPasting(object sender, DataObjectPastingEventArgs e){    if (e.DataObject.GetDataPresent(typeof(String)))    {        String text = (String)e.DataObject.GetData(typeof(String));        if (!IsTextAllowed(text))        {            e.CancelCommand();        }    }    else    {        e.CancelCommand();    }}

The event handler is previewing text input. Here a regular expression matches the text input only if it is not a number, and then it is not made to entry textbox.

If you want only letters then replace the regular expression as [^a-zA-Z].

XAML

<TextBox Name="NumberTextBox" PreviewTextInput="NumberValidationTextBox"/>

XAML.CS FILE

using System.Text.RegularExpressions;private void NumberValidationTextBox(object sender, TextCompositionEventArgs e){    Regex regex = new Regex("[^0-9]+");    e.Handled = regex.IsMatch(e.Text);}

I used some of what was already here and put my own twist on it using a behavior so I don't have to propagate this code throughout a ton of Views...

public class AllowableCharactersTextBoxBehavior : Behavior<TextBox>{    public static readonly DependencyProperty RegularExpressionProperty =         DependencyProperty.Register("RegularExpression", typeof(string), typeof(AllowableCharactersTextBoxBehavior),         new FrameworkPropertyMetadata(".*"));    public string RegularExpression    {        get        {            return (string)base.GetValue(RegularExpressionProperty);        }        set        {            base.SetValue(RegularExpressionProperty, value);        }    }    public static readonly DependencyProperty MaxLengthProperty =        DependencyProperty.Register("MaxLength", typeof(int), typeof(AllowableCharactersTextBoxBehavior),        new FrameworkPropertyMetadata(int.MinValue));    public int MaxLength    {        get        {            return (int)base.GetValue(MaxLengthProperty);        }        set        {            base.SetValue(MaxLengthProperty, value);        }    }    protected override void OnAttached()    {        base.OnAttached();        AssociatedObject.PreviewTextInput += OnPreviewTextInput;        DataObject.AddPastingHandler(AssociatedObject, OnPaste);    }    private void OnPaste(object sender, DataObjectPastingEventArgs e)    {        if (e.DataObject.GetDataPresent(DataFormats.Text))        {            string text = Convert.ToString(e.DataObject.GetData(DataFormats.Text));            if (!IsValid(text, true))            {                e.CancelCommand();            }        }        else        {            e.CancelCommand();        }    }    void OnPreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)    {        e.Handled = !IsValid(e.Text, false);    }    protected override void OnDetaching()    {        base.OnDetaching();        AssociatedObject.PreviewTextInput -= OnPreviewTextInput;        DataObject.RemovePastingHandler(AssociatedObject, OnPaste);    }    private bool IsValid(string newText, bool paste)    {        return !ExceedsMaxLength(newText, paste) && Regex.IsMatch(newText, RegularExpression);    }    private bool ExceedsMaxLength(string newText, bool paste)    {        if (MaxLength == 0) return false;        return LengthOfModifiedText(newText, paste) > MaxLength;    }    private int LengthOfModifiedText(string newText, bool paste)    {        var countOfSelectedChars = this.AssociatedObject.SelectedText.Length;        var caretIndex = this.AssociatedObject.CaretIndex;        string text = this.AssociatedObject.Text;        if (countOfSelectedChars > 0 || paste)        {            text = text.Remove(caretIndex, countOfSelectedChars);            return text.Length + newText.Length;        }        else        {            var insert = Keyboard.IsKeyToggled(Key.Insert);            return insert && caretIndex < text.Length ? text.Length : text.Length + newText.Length;        }    }}

Here is the relevant view code:

<TextBox MaxLength="50" TextWrapping="Wrap" MaxWidth="150" Margin="4" Text="{Binding Path=FileNameToPublish}" >     <interactivity:Interaction.Behaviors>         <v:AllowableCharactersTextBoxBehavior RegularExpression="^[0-9.\-]+$" MaxLength="50" />     </interactivity:Interaction.Behaviors></TextBox>