EmailValidationBehavior

Article
04/02/2024

The EmailValidationBehavior is a Behavior that allows users to determine whether or not text input is a valid e-mail address. For example, an Entry control can be styled differently depending on whether a valid or an invalid e-mail address is provided. The validation is achieved through a regular expression that is used to verify whether or not the text input is a valid e-mail address.

When attached to an InputView (e.g. Entry, Editor, etc.), EmailValidationBehavior will change the default Keyboard, Keyboard.Default, to Keyboard.Email. If a non-default Keyboard has been specified for the InputView, EmailValidationBehavior will not change the Keyboard.

When detached from an InputView, EmailValidationBehavior will change Keyboard.Email back to Keyboard.Default. If a Keyboard other than Keyboard.Email has been specified for the InputView, EmailValidationBehavior, will not change the Keyboard when detaching.

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 EmailValidationBehavior to an Entry and change the TextColor based on whether the entered text is a valid email address.

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 EmailValidationBehavior

The EmailValidationBehavior 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.EmailValidationBehaviorPage">

    <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:EmailValidationBehavior 
                InvalidStyle="{StaticResource InvalidEntryStyle}"
                ValidStyle="{StaticResource ValidEntryStyle}"
                Flags="ValidateOnValueChanged" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The EmailValidationBehavior can be used as follows in C#:

class EmailValidationBehaviorPage : ContentPage
{
    public EmailValidationBehaviorPage()
    {
        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 emailValidationBehavior = new EmailValidationBehavior
        {
            InvalidStyle = invalidStyle,
            ValidStyle = validStyle,
            Flags = ValidationFlags.ValidateOnValueChanged
        };

        entry.Behaviors.Add(emailValidationBehavior);

        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 EmailValidationBehaviorPage : ContentPage
{
    public EmailValidationBehaviorPage()
    {
        Content = new Entry()
            .Behaviors(new EmailValidationBehavior
            {
                InvalidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Red),
                ValidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Green),
                Flags = ValidationFlags.ValidateOnValueChanged
            });
    }
}

The following screenshot shows the resulting EmailValidationBehavior on Android: Screenshot of an EmailValidationBehavior 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.

Methods

Method	Description
EmailRegex (static)	A `GeneratedRegex` to match an input is a valid email address.
EmailDomainRegex (static)	A `GeneratedRegex` to match the domain of an email address.

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 EmailValidationBehavior over on the .NET MAUI Community Toolkit GitHub repository.

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