Xamarin.Forms - Validation using Xamarin Community Toolkit

In this blog post, you will learn how to validate xaml elements using Xamarin Community Toolkit in Xamarin.Forms App

Introduction

Xamarin.Forms code runs on multiple platforms - each of which has its own filesystem. This means that reading and writing files is most easily done using the native file APIs on each platform. Alternatively, embedded resources are a simpler solution to distribute data files with an app.

Xamarin Community Toolkit

Xamarin Community Toolkit is a collection of reusable elements for mobile development with Xamarin.Forms, including animations, behaviors, converters, effects, and helpers. It simplifies and demonstrates common developer tasks when building iOS, Android, macOS, WPF and UWP apps using Xamarin.Forms.

The Xamarin Community Toolkit is available as a Visual Studio NuGet package for new or existing Xamarin.Forms projects.

Validation Behaviours

1. CharactersValidationBehavior
2. EmailValidationBehavior
3. MultiValidationBehavior
4. NumericValidationBehavior
5. RequiredStringValidationBehavior
6. TextValidationBehavior
7. UriValidationBehavior

References

• https://docs.microsoft.com/en-us/xamarin/community-toolkit/behaviors/
• https://github.com/xamarin/XamarinCommunityToolkit

Prerequisites

• Visual Studio 2017 or later (Windows or Mac)

Let's Start

Setting up a Xamarin.Forms Project 

Start by creating a new Xamarin.Forms project. You will learn more by going through the steps yourself.

Create a new or existing Xamarin forms(.Net standard) Project. With Android and iOS Platform. 

Install Xamarin.CommunityToolkit NuGet

Install the following Nuget from Nuget Manager In your Visual Studio.

• Xamarin.CommunityToolkit

CharactersValidation

CharactersValidationBehavior is a behavior that allows the user to validate text input depending on specified parameters. 

Following CharacterType you can validate

	public enum CharacterType
	{
	/// <summary>Lowercase characters are allowed.</summary>
	LowercaseLetter = 1,
	/// <summary>Uppercase characters are allowed.</summary>
	UppercaseLetter = 2,
	/// <summary>Either lowercase characters or uppercase characters are allowed.</summary>
	Letter = LowercaseLetter | UppercaseLetter,
	/// <summary>Digits are allowed.</summary>
	Digit = 4,
	/// <summary>Characters and digits are allowed.</summary>
	Alphanumeric = Letter | Digit,
	/// <summary>Whitespace is allowed.</summary>
	Whitespace = 8,
	/// <summary>Non-alphanumeric symbols are allowed.</summary>
	NonAlphanumericSymbol = 16,
	/// <summary>Lowercase latin characters are allowed.</summary>
	LowercaseLatinLetter = 32,
	/// <summary>Uppercase latin characters are allowed.</summary>
	UppercaseLatinLetter = 64,
	/// <summary>Either latin lowercase characters or latin uppercase characters are allowed.</summary>
	LatinLetter = LowercaseLatinLetter | UppercaseLatinLetter,
	/// <summary>Any type of character or digit either lowercase or uppercase, latin or non-latin is allowed.</summary>
	Any = Alphanumeric | NonAlphanumericSymbol | Whitespace
	}

view raw CharType.cs hosted with ❤ by GitHub

Xaml Code

Here the sample is validating Numeric with 5 character.

	<Entry.Behaviors>
	<xct:CharactersValidationBehavior
	InvalidStyle="{StaticResource InvalidEntryStyle}"
	CharacterType="Digit"
	MaximumCharacterCount="5"
	/>
	</Entry.Behaviors>

view raw XAMLCode.xaml hosted with ❤ by GitHub

Result

The value should below 5 char only if it's greater than 5 it's shows error when you submit.

More info

https://docs.microsoft.com/en-us/xamarin/community-toolkit/behaviors/charactersvalidationbehavior

EmailValidation

EmailValidationBehavior is a behavior that allows users to determine whether or not text input is a valid email address.

Xaml code

	<Entry Placeholder="Email">
	<Entry.Behaviors>
	<xct:EmailValidationBehavior
	DecorationFlags="Trim"
	InvalidStyle="{StaticResource InvalidEntryStyle}"
	/>
	</Entry.Behaviors>
	</Entry>

view raw XAMLCode.xaml hosted with ❤ by GitHub

Regex validation

	<Entry Placeholder="Email">
	<Entry.Behaviors>
	<xct:EmailValidationBehavior
	RegexPattern="^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$"
	InvalidStyle="{StaticResource InvalidEntryStyle}"
	/>
	</Entry.Behaviors>
	</Entry>

view raw XAMLCode.xaml hosted with ❤ by GitHub

More info

https://docs.microsoft.com/en-us/xamarin/community-toolkit/behaviors/emailvalidationbehavior

Result

MultiValidation

MultiValidationBehavior is a behavior that allows the user to combine multiple validators to validate text input depending on specified parameters. For example, an Entry control can be styled differently depending on whether a valid or an invalid text input is provided.

Xaml code

	<Entry Placeholder="Password">
	<Entry.Behaviors>
	<xct:MultiValidationBehavior
	InvalidStyle="{StaticResource InvalidEntryStyle}">
	<xct:TextValidationBehavior
	MinimumLength="6" />
	<xct:CharactersValidationBehavior
	CharacterType="Digit"
	MinimumCharacterCount="1" />
	<xct:CharactersValidationBehavior
	CharacterType="LowercaseLetter"
	MinimumCharacterCount="1" />
	<xct:CharactersValidationBehavior
	CharacterType="UppercaseLetter"
	MinimumCharacterCount="1" />
	<xct:CharactersValidationBehavior
	CharacterType="NonAlphanumericSymbol"
	MinimumCharacterCount="1" />
	<xct:CharactersValidationBehavior
	CharacterType="Whitespace"
	MaximumCharacterCount="0" />
	</xct:MultiValidationBehavior>
	</Entry.Behaviors>
	</Entry>

view raw XAMLCode.xaml hosted with ❤ by GitHub

More info

https://docs.microsoft.com/en-us/xamarin/community-toolkit/behaviors/multivalidationbehavior

Result

Conclusion

I hope you have understood how to validate xaml elements using Xamarin Community Toolkit in Xamarin.Forms App

Thanks for reading. Please share your comments and feedback. Happy Coding :)