Fluent Validation With MVVM In Xamarin Forms Application

Introduction

Fluent Validation is used to create the validation logic separate from business logic for any type of object you want to validate. It's a kind of cross-cutting concern in application development and providing validation in the Aspect Oriented Programming structure.

Let us see how we can achieve the fluent validation in our Xamarin forms applications.

Implementation

Open Visual Studio and select New Project.

Select project type and give this project a name.



Select the template as Blank App and code sharing as PCL.

Set the target and minimum platform versions that your application will support.



Set the below configuration.



Open "Manage NuGet packages for Solutions" and install the following components.





The ViewModel directory will be added. This contains two files - MainViewModel.cs and ViewModelLocator.cs.

Create the Models folder and add the following files.

1. Create file cs.
   
   1. namespace FluentValidationDemo1.Models
   2. {
   3. public class User
   4. {
   5. public string UserName { get; set; }
   6. public string Password { get; set; }
   7. public string ConfirmPassword { get; set; }
   8. public string Email { get; set; }
   9. }
   10. }

2. Create file cs.
   
   1. using FluentValidation;
   3. namespace FluentValidationDemo1.Models
   4. {
   5. [FluentValidation.Attributes.Validator(typeof(UserValidator))]
   6. public class UserValidator : AbstractValidator<User>
   7. {
   8. public UserValidator()
   9. {
   10. RuleFor(x => x.UserName).NotNull().Length(10, 20);
   11. RuleFor(x => x.Password).NotNull();
   12. RuleFor(x => x.ConfirmPassword).NotNull().Equal(x => x.Password);
   13. RuleFor(x => x.Email).NotNull().EmailAddress();
   14. }
   15. }
   16. }

We have to define the validation attributes for the class you want to validate.

Inside ViewModel folder, create a file named SignUpPageViewModel.cs.