MaxLengthReachedBehavior

The MaxLengthReachedBehavior is a Behavior that allows the user to trigger an action when a user has reached the maximum length allowed on an InputView. It can either trigger a Command or an event depending on the user's preferred scenario. Both the Command and event will include the resulting text of the InputView.

Additionally it is possible to dismiss the keyboard when the maximum length is reached via the ShouldDismissKeyboardAutomatically property which defaults to false.

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

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 MaxLengthReachedBehavior

The MaxLengthReachedBehavior 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.MaxLengthReachedBehaviorPage"
    x:Name="Page">

    <Entry Placeholder="Start typing until MaxLength is reached..."
           MaxLength="100">
        <Entry.Behaviors>
            <toolkit:MaxLengthReachedBehavior 
                Command="{Binding Source={x:Reference Page}, Path=BindingContext.MaxLengthReachedCommand}" />
        </Entry.Behaviors>
    </Entry>

</ContentPage>

C#

The MaxLengthReachedBehavior can be used as follows in C#:

class MaxLengthReachedBehaviorPage : ContentPage
{
    public MaxLengthReachedBehaviorPage()
    {
        var entry = new Entry
        {
            Placeholder = "Start typing until MaxLength is reached...",
            MaxLength = 100
        };

        var behavior = new MaxLengthReachedBehavior();
        behavior.SetBinding(
            MaxLengthReachedBehavior.CommandProperty,
            new Binding(
                nameof(ViewModel.MaxLengthReachedCommand)
            )
        );

        entry.Behaviors.Add(behavior);

        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 MaxLengthReachedBehaviorPage : ContentPage
{
    public MaxLengthReachedBehaviorPage()
    {
        Content = new Entry
        {
            Placeholder = "Start typing until MaxLength is reached...",
            MaxLength = 100
        }.Behaviors(
            new MaxLengthReachedBehavior().Bind(
                MaxLengthReachedBehavior.CommandProperty,
                static (ViewModel vm) => vm.MaxLengthReachedCommand));
    }
}

Properties

Property	Type	Description
Command	ICommand	The command that is executed when the user has reached the maximum length. The parameter of the command will contain the Text of the InputView.
ShouldDismissKeyboardAutomatically	bool	Indicates whether or not the keyboard should be dismissed automatically when the maximum length is reached.

Events

Event	Description
MaxLengthReached	The event that is raised when the user has reached the maximum length. The event args will contain the Text of the InputView.

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