Angular Reactive Forms Example

Reactive forms ( also known as Model-driven forms) are one of the two ways to build Angular forms. In this tutorial, we will learn how to build a simple Example Reactive Form. To build reactive forms, first, we need to import ReactiveFormsModule. We then create the Form Model in component class using Form Group, Form Control & FormArrays. Next, we will create the HTML form template and bind it to the Form Model.

What are Reactive Forms?

Reactive forms are forms where we define the structure of the form in the component class. i.e. we create the form model with Form Groups, Form Controls, and FormArrays. We also define the validation rules in the component class. Then, we bind it to the HTML form in the template. This is different from the template-driven forms, where we define the logic and controls in the HTML template.

How to use Reactive Forms

  1. Import ReactiveFormsModule
  2. Create Form Model in component class using FormGroup, FormControl & FormArrays
  3. Create the HTML Form resembling the Form Model.
  4. Bind the HTML Form to the Form Model

Reactive Forms Example Application

Use ng new to create a new application

Run ng serve and verify if everything is installed correctly.

Import ReactiveFormsModule

To work with Reactive forms, we must import the ReactiveFormsModule. We usually import it in root module or in a shared module. The ReactiveFormsModule contains all the form directives and constructs for working with angular reactive forms.

Model

In the template-driven approach, we used ngModel & ngModelGroup directive on the HTML elements. The FormsModule automatically creates the FormGroup & FormControl instances from the HTML template. This happens behind the scene.

In the Reactive Forms approach, It is our responsibility to build the Model using FormGroupFormControl and FormArray.

The FormGroup, FormControl & FormArray are the three building blocks of the Angular Forms. We learned about them in the Angular Forms Tutorial.

FormControl encapsulates the state of a single form element in our form. It stores the value and state of the form element and helps us to interact with them using properties & methods.

FormGroup represents a collection of form controls. It can also contain other FormGroups and FormArrays. In fact, an angular form is a FormGroup.

Let’s create the model for our Form.

First, we need to import FormGroupFormControl & Validator from the @angular/forms. Open the app.component.ts and the add following import statement.


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Creating the Form Model

The FormGroup is created with the following syntax

In the above, we have created an instance of a FormGroup and named it as contactForm. The contactForm is top level FormGroup and is the name of our form model.

The FormGroup takes 3 arguments. a collection of a child controls (which can be FormControl, FormArray, or another FormGroup), a validator, and an asynchronous validator. The validators are optional.

Adding the Child Controls

The next step is to add the child controls to the contactForm.

The first argument to FormGroup is the collection of controls. The Controls can be FormControl, FormArray or another FormGroup. It can be done by creating a new instance for FormControl (or FormGroup or FormArray)

In the above example, we have added five FormControl instances each representing the properties firstname. lastname.email, gender, ismarried & country.

The Other two arguments to FormGroup are Sync Validator & Async Validator. They are optional.

With this our model is ready.

HTML Form

The next task is to build an HTML form. The following is a regular HTML form. We enclose it in a <form> tag. We have included two text inputs (FirstName & LastName), an email field, a radio button (gender), a checkbox (isMarried), and a select list (country). These are simple HTML Form elements.

Binding the template to the model

Now we need to associate our model with the above HTML Template. We need to tell angular that we have a model for the form.

This is done using the formGroup directive as shown below.

We use the square bracket (one-way binding) around FormGroup directive and assign our form model (i.e. contactForm name that we gave to our model in the component class) to it.

Next, we need to bind each form field to an instance of the FormControl models. We use the FormControlName directive for this. We add this directive to every form field element in our form. The value is set to the name of the corresponding FormControl instance in the component class.

Submit form

We submit the form data to the component using the Angular directive named ngSubmit.  Note that we already have a submit button in our form. The ngSubmit directive binds itself to the click event of the submit button. We are using event binding (parentheses) to bind ngSubmit to OnSubmit method. When the user clicks on the submit button ngSubmit invokes the OnSubmit method on the Component class

We are yet to add the onSubmit() method in the component class. Hence the Angular will throw an error here.

Final Template

Our Final Template is as shown below

Receive the data in the Component class

The last step is to receive the form data in the component class. All we need to do is to create the onSubmit method in our component class.

We are using the console.log(this.contactForm.value) to send the value of our form data to the console window.

The final component class is shown below.

Test the form

Now you can run the app and see the result. Open the developer console and see the value returned by the contactForm.value. The values of the form are returned as JSON object, which you can pass it your backend API to persist the information to the database.

FormControl

A FormControl takes 3 arguments. a default value, a validator, and an asynchronous validator. All of them are optional.

Default Value

You can pass a default value either as a string or as an object of key-value pair. When you pass an object you can set both the value and the whether or not the control is disabled.

Sync Validator

The second parameter is an array of sync Validators. Angular has some built-in Validators such as required and minLength etc.

You can pass the Validator function as shown below.

Asynchronous validator

The third argument is the Async Validator. The syntax of Async Validators is similar to Sync Validators.

More on validation in our next tutorial Validations in Reactive forms.

Grouping the controls using FormGroup

We can group various FormControls together. For Example fields such as street, city, country and Pincode each will have their own FormControl but can be grouped together as an address FormGroup

In the code above, we have created new FormGroup Address and added three form controls i.e citystreet, country & Pincode

In the template use the formGroupName directive to enclose the control using a div element as shown below

Summary

We learned how to build Angular Reactive Forms in this tutorial. In the next tutorial, we will add validation rules to our application.

  1. Angular Forms Tutorial: Fundamental & Concepts
  2. Template Driven Forms in Angular
  3. Set Value in Template Driven forms in Angular
  4. Reactive Forms in Angular
  5. FormBuilder in Reactive Forms
  6. SetValue & PatchValue in Angular
  7. StatusChanges in Angular Forms
  8. ValueChanges in Angular Forms
  9. FormControl
  10. FormGroup
  11. FormArray Example
  12. Build Dynamic or Nested Forms using FormArray
  13. Validations in Reactive Forms in Angular
  14. Custom Validator in Reactive Forms
  15. Passing Parameter to Custom Validator in Reactive Forms
  16. Inject Service into Custom Validator
  17. Validation in Template Driven Forms
  18. Custom Validator in Template Driven Forms

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