Angular Reactive Forms Susan Adelokiki NG2 - MEETUP 

Hello ● Susan Adelokiki ● Software Developer at Andela ● More about me at susanadelokiki.com 

Forms Forms are very effective for business applications to help users interact with software. 

Angular Forms With Angular, we have the liberty to choose between two major form building techniques in receiving and accepting user input ● Template-driven Forms ● Reactive Forms 

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Angular form-building blocks Angular makes use of building blocks to generate the form model. The building blocks are used by both reactive and template-driven forms. They are called FormGroup and FormControl. 

FormGroup and FormControl ● The FormGroup tracks values and states of the form controls. It takes the existing formGroup instance and matches it with an HTML element. ● The Form Control tracks values and states of input elements. ● Instances of this building block create the form model 

Form Model ● It represents the HTML structure ● It retains form states such as dirty, valid, invalid, etc. ● It is different from the data model. ● It is the same for template-driven and reactive forms but created differently. ● For template-driven forms, Angular generates the form model ● For reactive forms, Angular does not generate the form model rather it is generated from instances of the FormGroup and FormControl. 

Template-Driven Forms In Template-Driven forms, Responsibility for the form is heavy on the template with html and data-binding. ● Uses two way data-binding with the [(ngModel)] syntax to keep user entry and data model property in sync. ● Suitable for simple scenarios ● Angular generates Form Model by creating the instances FormGroup and FormControl 

Component Template 

Component Class 

Template-Driven Form Properties From previous image, we see that: ● It makes use of event-binding to submit ● It leverages HTML5 validation ● It leverages data-binding using ngModel 

Strengths of the Template-Driven Forms ● Straightforward and simple to use ● No need to write code to copy data into the input elements. Angular automatically generates them. ● Angular Automatically tracks the form and its data ● Minimal component code 

Weaknesses of Template-Driven Forms ● It does not provide the flexibility of creating form controls, Angular directives generates those controls based on information in the data-binding. ● Adding more & more validators to the input tag eventually makes it unreadable ● Template-driven forms are asynchronous and hence makes unit testing a little more complicated. 

Building a Simple Reactive Form ● Import your building blocks ● Specify a property for the root formGroup ● Create an instance of the FormGroup ● Update AngularModule by adding ReactiveFormsModule to the imports array and declarations ● Bind the form to the formGroup and the input elements to the associated formControl using the reactive form directives. 

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Accessing Form Model Properties We can access the form model in two ways: ● Form Model Heirarchy E.g To access if the firstname input element is valid: CustomerForm.controls.firstName.valid ● Referencing the form control using the Form Group’s get method. CustomerForm.get(‘firstName’).valid 

setValue & patchValue These methods are used to initialize or reset values in the Form model 

Validation To implement validation, we simply import the Validators from @angular/forms. We then pass them in as a second argument to our formControl instances. 

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Form Builder The Form Builder is useful when our forms get bigger and we have multiple form groups. It reduces repetition and clutter by handling control creation. ● Import the FormBuilder, we can take off the FormControl import. ● Inject the FormBuilder in the constructor. ● Use the FormBuilder instance to create the formGroup. 

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Which is better? Template-driven forms is useful in making small scale apps which do not necessarily require control of the forms by the user. Reactive forms are very useful in more complex scenarios and large scale apps because there is flexibility on the form model and form building blocks and unit testing can easily be done. 

Thank You! 

DEMO 

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