Allow only numeric entry in WPF Text Box

I will like to validate user entry to ensure they are integers. How can I do it? I thought of using IDataErrorInfo which seems like the "correct" way to do validation in WPF. So I tried implementing it, in my ViewModel.

But the thing is my text box is bound to an integer field, and there isn't a开发者_StackOverflow社区ny need to validate if an int is an int. I noticed that WPF automatically adds a red border around the textbox to notify the user of the error. The underlying property doesn't change to an invalid value. But I would like to notify the user of this. How can I do it?

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Another way is simply to not allow values that are not integers. The following implementation is a little bit sucky, and I would like to abstract it later on in order for it to be more reusable, but here is what I did:

in the code behind in my view (I know this is might hurt if you are a hardcore mvvm ;o) ) I defined the following functions :

  private void NumericOnly(System.Object sender, System.Windows.Input.TextCompositionEventArgs e)
{
    e.Handled = IsTextNumeric(e.Text);

}


private static bool IsTextNumeric(string str)
{
    System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex("[^0-9]");
    return reg.IsMatch(str);

}

And in the XAML view, every textbox that was only supposed to accept integers was defined like this:

   <TextBox Padding="2"  TextAlignment="Right" PreviewTextInput="NumericOnly" Text="{Binding xxx.yyyy}" MaxLength="1" />

The key attribute being PreviewTextInput

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The red border you've seen is actually a ValidationTemplate, which you can extend and add a info for the user. See this example:

    <UserControl.Resources>
        <ControlTemplate x:Key="validationTemplate">
            <Grid>
                <Label Foreground="Red" HorizontalAlignment="Right" VerticalAlignment="Center">Please insert a integer</Label>
                <Border BorderThickness="1" BorderBrush="Red">
                    <AdornedElementPlaceholder />
                </Border>
            </Grid>
        </ControlTemplate>
    </UserControl.Resources>

<TextBox Name="tbValue" Validation.ErrorTemplate="{StaticResource validationTemplate}">

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We can do validation on text box changed event. The following implementation prevents keypress input other than numeric and one decimal point.

private void textBoxNumeric_TextChanged(object sender, TextChangedEventArgs e)
{
        TextBox textBox = sender as TextBox;
        Int32 selectionStart = textBox.SelectionStart;
        Int32 selectionLength = textBox.SelectionLength;
        String newText = String.Empty;
        int count = 0;
        foreach (Char c in textBox.Text.ToCharArray())
        {
            if (Char.IsDigit(c) || Char.IsControl(c) || (c == '.' && count == 0))
            {
                newText += c;
                if (c == '.')
                    count += 1;
            }
        }
        textBox.Text = newText;
        textBox.SelectionStart = selectionStart <= textBox.Text.Length ? selectionStart : textBox.Text.Length;    
}

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if you are working in WPF Better to use PreviewTextInput event which support all platforms and from presentationcore.dll

here is the example:

private void TextBox_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
    {
        if ((e.Text) == null || !(e.Text).All(char.IsDigit))
        {
            e.Handled = true;
        }
    }

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Here is how to create a numeric field in WPF, using the regular expressions.

XAML:

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

Code behind:

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