text-validation-behavior.md

title	author	description	ms.date
TextValidationBehavior - .NET MAUI Community Toolkit	bijington	The TextValidationBehavior is a Behavior that allows the user to validate a given text depending on specified parameters.	04/20/2022

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.

[!INCLUDE important note on bindings within 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

[!INCLUDE XAML usage guidance]

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.

[!INCLUDE common validation properties]

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.