NumericValidationBehavior

Article
04/02/2024

The NumericValidationBehavior is a Behavior that allows the user to determine if text input is a valid numeric value. For example, an Entry control can be styled differently depending on whether a valid or an invalid numeric 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 NumericValidationBehavior to an Entry and change the TextColor when the number entered is considered invalid (not between 1 and 100).

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 NumericValidationBehavior

The NumericValidationBehavior 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.NumericValidationBehaviorPage">

    <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 Keyboard="Numeric">
        <Entry.Behaviors>
            <toolkit:NumericValidationBehavior 
                InvalidStyle="{StaticResource InvalidEntryStyle}"
                ValidStyle="{StaticResource ValidEntryStyle}"
                Flags="ValidateOnValueChanged"
                MinimumValue="1.0"
                MaximumValue="100.0"
                MaximumDecimalPlaces="2" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The NumericValidationBehavior can be used as follows in C#:

class NumericValidationBehaviorPage : ContentPage
{
    public NumericValidationBehaviorPage()
    {
        var entry = new Entry
        {
            Keyboard = Keyboard.Numeric
        };

        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 numericValidationBehavior = new NumericValidationBehavior
        {
            InvalidStyle = invalidStyle,
            ValidStyle = validStyle,
            Flags = ValidationFlags.ValidateOnValueChanged,
            MinimumValue = 1.0,
            MaximumValue = 100.0,
            MaximumDecimalPlaces = 2
        };

        entry.Behaviors.Add(numericValidationBehavior);

        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 NumericValidationBehaviorPage : ContentPage
{
    public NumericValidationBehaviorPage()
    {
        Content = new Entry
        {
            Keyboard = Keyboard.Numeric
        }.Behaviors(new NumericValidationBehavior
        {
            InvalidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Red),
            ValidStyle = new Style<Entry>(Entry.TextColorProperty, Colors.Green),
            Flags = ValidationFlags.ValidateOnValueChanged,
            MinimumValue = 1.0,
            MaximumValue = 100.0,
            MaximumDecimalPlaces = 2
        });
    }
}

Properties

Property	Type	Description
`MaximumDecimalPlaces`	`double`	The maximum number of decimal places that will be allowed.
`MinimumDecimalPlaces`	`double`	The minimum number of decimal places that will be allowed.
`MaximumValue`	`double`	The maximum numeric value that will be allowed.
`MinimumValue`	`double`	The minimum numeric value that 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 NumericValidationBehavior over on the .NET MAUI Community Toolkit GitHub repository.

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