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Basic steps to create Reactive forms and Form Validation

Basic steps to create Reactive forms and Form Validation:

 

Know about Angular Forms:

Angular forms are used to deal with user inputs. It can include a massive no of input fields, spanning more than one tab. Forms may include complicated validation logic interdependent on multiple fields.

Some things forms are anticipated to do

  • Initialize the forms fields and gift them to the user
  • Collect the user information
  • Track adjustments made to the fields
  • Validate the inputs
  • Display useful errors(mistakes) to the user

Angular forms module offers all the above services. It binds the form field values to the Angular component class. It tracks adjustments made to the form fields in order that we can respond accordingly. The Angular forms will provide the built-in validators to validate the inputs.

Multiple approaches in angular forms creation:

There are 2 approaches to dealing with user input through forms:

  • Reactive forms
  • Template-driven forms

 

Reactive Forms  approach

In Reactive Forms or Model-driven approaches, the logic of the form is described in the component as an object. The Model-driven approach has extra blessings as it makes the testing of the component easier.

 

Template-driven forms approach

In Template-driven approach is the simplest way to build the Angular forms. Template contains the logic of the form.

 

Steps to create Reactive Forms  and custom validator:

Angular reactive forms follow a model-driven approach to handle form input whose values may be modified over time. These are also referred to as model-driven forms. In component class we can define the structure of the form. We can create the form model with Form Groups, Form Controls, and Form Arrays. We can create and update multiple form controls and define the validation rules in the component class. Create the HTML Form resembling the Form Model and bind the HTML Form to the Form Model.

 

1. Register the reactive forms module

You have to import ReactiveFormsModule from the @angular/forms package and add it to NgModule’s imports array to use reactive forms.

Graphical user interface, text, application

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2. Generate and Import a new form control

First step: Generate a component for the control by running the following command:

ng generate component create-edit-person-form

The FormControl class is the fundamental constructing block used in reactive forms. To create and use a form control, you have to import the FormControl class into your component. Create a new instance of this form control to save it as a class property.

Write the following code in create-edit-person-form.component.ts file:

Graphical user interface, text, application

Description automatically generated3. Now, register the control in the HTML form

After creating the control in the component class, you have to add it to the form control element in the HTML form template. Following is a regular HTML form which is enclosed with

tag. The template can be updated using formControl binding.

Graphical user interface, text, application

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We have registered the form controls that are declared in .ts file to the input elements in the HTML template. Now, the form control and DOM element communicate with each other, and the view reflects changes in the model, and vice versa.

 

Create the validation service:

Run below command to create a new service:

ng g s servicescustomvalidation

 

This command will create a folder. Open the customvalidation.service.ts file and put the following code in it:

Graphical user interface, text

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The PasswordPatternValidator method  is used to validate the password pattern in our form.

Regular expression is used to validate the password and if the check fails, the invalidPassword property is to true.

Conclusion:

This explains simple steps to create an angular reactive form and how to validate form inputs. The reactive forms are more flexible and handles complex scenarios. Reactive form module allows us to build the form model and offers an easy way to use reactive patterns and validations. And there are some extra benefits when you can do this when compared to template forms like easier unit testing.  

We have used some of the built-in validators like email and required. There are many more built-in angular form validators like minLength, maxLength, pattern, etc.

We also can easily add custom validation on single fields as well as multiple fields combined in the form. Reactive forms are a little bit of a change from traditional template-driven forms, but there are some distinct benefits to using them.

About the Author:

Madhuchandra Nagaraj is a full stack developer currently @Version1 with around 5 years of experience in technologies such as .NET, Azure, Devops, Angular, SQL, PowerApps. Apart from these technologies he has worked on SAP BW/BI and SAP HANA. He enjoys working on exploring new technologies.

LinkedIn: https://www.linkedin.com/in/madhuchandra-n-988127106/

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