CharactersValidationBehavior

The CharactersValidationBehavior is a Behavior that allows the user to validate text input depending on specified parameters. For example, an Entry control can be styled differently depending on whether a valid or an invalid text value is provided. This behavior includes built-in checks such as checking for a certain number of digits or alphanumeric characters.

Important

The .NET MAUI Community Toolkit Behaviors do not set the BindingContext of a behavior, because behaviors can be shared and applied to multiple controls through styles. For more information refer to .NET MAUI Behaviors

Syntax

The following examples show how to add the CharactersValidationBehavior to an Entry and change the TextColor based on whether the entered text only contains numbers and have at least 2 numbers.

XAML

Including the XAML namespace

In order to use the toolkit in XAML the following xmlns needs to be added into your page or view:

xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"

Therefore the following:

<ContentPage
    x:Class="CommunityToolkit.Maui.Sample.Pages.MyPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">

</ContentPage>

Would be modified to include the xmlns as follows:

<ContentPage
    x:Class="CommunityToolkit.Maui.Sample.Pages.MyPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit">

</ContentPage>

Using the CharactersValidationBehavior

The CharactersValidationBehavior can be used as follows in XAML:

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
             x:Class="CommunityToolkit.Maui.Sample.Pages.Behaviors.CharactersValidationBehaviorPage">

    <ContentPage.Resources>
        <Style x:Key="InvalidEntryStyle" TargetType="Entry">
            <Setter Property="TextColor" Value="Red" />
        </Style>
        <Style x:Key="ValidEntryStyle" TargetType="Entry">
            <Setter Property="TextColor" Value="Green" />
        </Style>
    </ContentPage.Resources>

    <Entry>
        <Entry.Behaviors>
            <toolkit:CharactersValidationBehavior 
                InvalidStyle="{StaticResource InvalidEntryStyle}"
                ValidStyle="{StaticResource ValidEntryStyle}"
                Flags="ValidateOnValueChanged"
                CharacterType="Digit"
                MinimumCharacterTypeCount="3" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The CharactersValidationBehavior can be used as follows in C#:

class CharactersValidationBehaviorPage : ContentPage
{
    public CharactersValidationBehaviorPage()
    {
        var entry = new Entry();

        var validStyle = new Style(typeof(Entry));
        validStyle.Setters.Add(new Setter
        {
            Property = Entry.TextColorProperty,
            Value = Colors.Green
        });

        var invalidStyle = new Style(typeof(Entry));
        invalidStyle.Setters.Add(new Setter
        {
            Property = Entry.TextColorProperty,
            Value = Colors.Red
        });

        var charactersValidationBehavior = new CharactersValidationBehavior
        {
            InvalidStyle = invalidStyle,
            ValidStyle = validStyle,
            Flags = ValidationFlags.ValidateOnValueChanged,
            CharacterType = CharacterType.Digit,
            MinimumCharacterTypeCount = 3
        };

        entry.Behaviors.Add(charactersValidationBehavior);

        Content = entry;
    }
}

C# Markup

Our CommunityToolkit.Maui.Markup package provides a much more concise way to use this Behavior in C#.

using CommunityToolkit.Maui.Markup;

class CharactersValidationBehaviorPage : ContentPage
{
    public CharactersValidationBehaviorPage()
    {
        Content = new Entry()
            .Behaviors(new CharactersValidationBehavior
            {
                InvalidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Red),
                ValidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Green),
                Flags = ValidationFlags.ValidateOnValueChanged,
                CharacterType = CharacterType.Digit,
                MinimumCharacterTypeCount = 3
            });
    }
}

The following screenshot shows the resulting CharactersValidationBehavior on Android:

Properties

Property	Type	Description
CharacterType	CharacterType	Provides an enumerated value to use to set how to handle comparisons.
DecorationFlags	TextDecorationFlags	Provides enumerated value to use to set how to handle white spaces.
MaximumCharacterTypeCount	int	The maximum number of CharacterType characters required.
MaximumLength	int	The maximum length of the value that will be allowed.
MinimumCharacterTypeCount	int	The minimum number of CharacterType characters required.
MinimumLength	int	The minimum length of the value that will be allowed.
RegexOptions	RegexOptions	Provides enumerated values to use to set regular expression options.
RegexPattern	string	The regular expression pattern which the value will have to match before it will be allowed.

ValidationBehavior Properties

The following properties are implemented in the base class, public abstract class ValidationBehavior:

Property	Type	Description
Flags	ValidationFlags	Provides an enumerated value that specifies how to handle validation.
ForceValidateCommand	ICommand	Allows the user to provide a custom ICommand that handles forcing validation.
InvalidStyle	Style	The Style to apply to the element when validation fails.
IsNotValid	bool	Indicates whether or not the current value is considered not valid.
IsRunning	bool	Indicates whether or not the validation is in progress now (waiting for an asynchronous call is finished).
IsValid	bool	Indicates whether or not the current value is considered valid.
ValidStyle	Style	The Style to apply to the element when validation is successful.
Value	object	The value to validate.
ValuePropertyName	string	Allows the user to override the property that will be used as the value to validate.

Examples

You can find an example of this behavior in action in the .NET MAUI Community Toolkit Sample Application.

API

You can find the source code for CharactersValidationBehavior over on the .NET MAUI Community Toolkit GitHub repository.