WPF ValidationRule to check if a TextBox contains only alphabets

Question

I am trying to implement ValidationRule to validate that user enters only alphabets in a TextBox. My following code is a bit different than the above linked example where the properties Min and Max are the fixed numbers; whereas in my case the property AlphabetsOnly contains range of alphabets.

Question: In the following part of the MainWindow.xaml file (shown at the bottom) what should I replace ???? with? I found something similar here, but they have declared a property MustEndWith that indicates the value should end with a word .def - that is different than saying all characters must be alphabets.

<Binding.ValidationRules>
     <local:AlphabetsOnlyValidationRule AlphabetsOnly="????" />
</Binding.ValidationRules>

Code:

public class AlphabetsOnlyValidationRule : ValidationRule
{
    public string AlphabetsOnly { get; set; }

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        string sVal = value as string;

        if (sVal == null)
        {
            return new ValidationResult(false, "Please enter some text");
        }

        if (!sVal.ToList().All(c=>char.IsLetter(c)))
        {
            return new ValidationResult(false, "First Name should contains alphabets only"));
        }

        return new ValidationResult(true, null);
    }
}

MainWindow.xaml:

<Window x:Class="WPF_DeleteNow.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        .....
        xmlns:local="clr-namespace:MyWPFProject"
        mc:Ignorable="d">

    <Window.Resources>
        <local:AlphabetsOnlyValidationRule x:Key="AlphabetsOnlyKey"/>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            .....
        </Grid.RowDefinitions>
        <TextBox Name="txtFirstName">
            <TextBox.Text>
                <Binding Path="FirstName" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <local:AlphabetsOnlyValidationRule AlphabetsOnly="??????" />
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
    </Grid>
</Window>

What is the `AlphabetsOnly` supposed to be set to in your example? — mm8, Sep 01 '20 at 18:49
@mm8 Yes, that is my confusion. As you may have noticed in block `if (!sVal.ToList().All(c=>char.IsLetter(c))){...}` I'm checking if the text value contains only `alphabets`. But I'm note sure what should `AlphabetsOnly` be set to. Any comments/suggestions? I know in RegEx we do something like `[a-zA-Z]` but I'm not sure in the above class what `AlphabetsOnly` would be set to. — nam, Sep 01 '20 at 19:01
If you don't know why you need the property or what to set it to, why don't you just remove it? — mm8, Sep 01 '20 at 19:01

score 1 · Accepted Answer · answered Sep 01 '20 at 19:21

You don't need a property to verify that the string contains only alphabetical letters. Just remove the AlphabetsOnly property and use a regular expression to perform the validation:

public class AlphabetsOnlyValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        string sVal = value as string;

        if (string.IsNullOrEmpty(sVal))
        {
            return new ValidationResult(false, "Please enter some text");
        }

        if (System.Text.RegularExpressions.Regex.IsMatch(sVal, @"^[a-zA-Z]+$"))
        {
            return new ValidationResult(false, "First Name should contains alphabets only");
        }

        return new ValidationResult(true, null);
    }
}

WPF ValidationRule to check if a TextBox contains only alphabets

1 Answers1