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RequiredStringValidationBehavior

The RequiredStringValidationBehavior is a Behavior that allows the user to determine if text input is equal to specific text. For example, an Entry control can be styled differently depending on whether a valid or an invalid text input is provided.

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 RequiredStringValidationBehavior to an Entry and change the TextColor based on whether the RequiredString has been entered.

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 RequiredStringValidationBehavior

The RequiredStringValidationBehavior 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.RequiredStringValidationBehaviorPage">

    <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:RequiredStringValidationBehavior 
                InvalidStyle="{StaticResource InvalidEntryStyle}"
                ValidStyle="{StaticResource ValidEntryStyle}"
                Flags="ValidateOnValueChanged"
                RequiredString="MAGIC ANSWER" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The RequiredStringValidationBehavior can be used as follows in C#:

class RequiredStringValidationBehaviorPage : ContentPage
{
    public RequiredStringValidationBehaviorPage()
    {
        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 requiredStringValidationBehavior = new RequiredStringValidationBehavior
        {
            InvalidStyle = invalidStyle,
            ValidStyle = validStyle,
            Flags = ValidationFlags.ValidateOnValueChanged,
            RequiredString = "MAGIC ANSWER"
        };

        entry.Behaviors.Add(requiredStringValidationBehavior);

        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 RequiredStringValidationBehaviorPage : ContentPage
{
    public RequiredStringValidationBehaviorPage()
    {
        Content = new Entry()
            .Behaviors(new RequiredStringValidationBehavior
            {
                InvalidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Red),
                ValidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Green),
                Flags = ValidationFlags.ValidateOnValueChanged,
                RequiredString = "MAGIC ANSWER"
            });
    }
}

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

Properties

Property Type Description
ExactMatch bool Determines whether the entered text must match the whole contents of the RequiredString property or simply contain the RequiredString property value.
RequiredString string The string that will be compared to the value provided by the user.

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

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