TextValidationBehavior

The TextValidationBehavior is a Behavior that allows the user to validate a given text depending on specified parameters. By adding this behavior to any InputView control it can be styled differently depending on whether a valid or an invalid text value is provided. It offers various built-in checks such as checking for a certain length or whether or not the input value matches a specific regular expression.

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 TextValidationBehavior to an Entry and change the TextColor based on whether the entered text is between 1 and 10 characters long.

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 TextValidationBehavior

The TextValidationBehavior 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.TextValidationBehaviorPage">

    <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:TextValidationBehavior 
                InvalidStyle="{StaticResource InvalidEntryStyle}"
                ValidStyle="{StaticResource ValidEntryStyle}"
                Flags="ValidateOnValueChanged"
                MinimumLength="1"
                MaximumLength="10" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The TextValidationBehavior can be used as follows in C#:

class TextValidationBehaviorPage : ContentPage
{
    public TextValidationBehaviorPage()
    {
        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 textValidationBehavior = new TextValidationBehavior
        {
            InvalidStyle = invalidStyle,
            ValidStyle = validStyle,
            Flags = ValidationFlags.ValidateOnValueChanged,
            MinimumLength = 1,
            MaximumLength = 10
        };

        entry.Behaviors.Add(textValidationBehavior);

        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 TextValidationBehaviorPage : ContentPage
{
    public TextValidationBehaviorPage()
    {
        Content = new Entry()
            .Behaviors(new TextValidationBehavior
            {
                InvalidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Red),
                ValidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Green),
                Flags = ValidationFlags.ValidateOnValueChanged,
                MinimumLength = 1,
                MaximumLength = 10
            });
    }
}

The following screenshot shows the resulting TextValidationBehavior on Android:

Properties

Property	Type	Description
DecorationFlags	TextDecorationFlags	Provides enumerated value to use to set how to handle white spaces.
MaximumLength	int	The maximum length of the value that will be allowed.
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 TextValidationBehavior over on the .NET MAUI Community Toolkit GitHub repository.