Breaking down a form into several sections for validation purposes

Question

Breaking down a form into several sections for validation purposes

I am attempting to build a large form using Angular 2, but I would like to structure it with multiple components. Here is an example of what I have in mind.

App component

<form novalidate #form1="ngForm" [formGroup]="myForm">
<div>
    <address></address>
</div>
<div>
    <input type="text" ngModel required/>
</div>

<input type="submit" [disabled]="!form1.form.valid" > </form>

Address component

<div>
<input type="text" ngModel required/> </div>

After implementing the above code, I noticed that the form appeared correctly in the browser. However, there was an issue with the submit button. It remained enabled even after deleting text from the address component. Strangely, it worked fine when deleting text from the input box in the app component.

angular typescript angular-forms

Answer 1

Answer №1

If you're looking for a cleaner way to handle forms, I recommend using a reactive form. Regarding your question:

Is there another example that doesn't involve loops?

Sure, I can provide you with an alternative example. You just need to nest a FormGroup and pass it to the child component.

For instance, if your form has this structure and you want to pass the address FormGroup to the child:

ngOnInit() {
  this.myForm = this.fb.group({
    name: [''],
    address: this.fb.group({ 
      street: [''],
      zip: ['']
    })
  })
}

In the parent component, simply forward the nested FormGroup:

<address [address]="myForm.get('address')"></address>

In the child component, use @Input for the nested FormGroup:

@Input() address: FormGroup;

In the template of the child component, bind the FormGroup using [formGroup]:

<div [formGroup]="address">
  <input formControlName="street">
  <input formControlName="zip">
</div>

If you prefer not to create a nested FormGroup, you can directly pass the parent form to the child. For example:

this.myForm = this.fb.group({
  name: [''],
  street: [''],
  zip: ['']
})

You have the flexibility to choose which controls to display in the child component. Following the previous example, if we only want to show street and zip, the child tag within the template would be:

<address [address]="myForm"></address>

Check out this

Demo demonstrating the first option, or explore the second Demo

For more insights on nested model-driven forms, visit this resource.

Answer 2

If you're looking for a cleaner way to handle forms, I recommend using a reactive form. Regarding your question:

Is there another example that doesn't involve loops?

Sure, I can provide you with an alternative example. You just need to nest a FormGroup and pass it to the child component.

For instance, if your form has this structure and you want to pass the address FormGroup to the child:

ngOnInit() {
  this.myForm = this.fb.group({
    name: [''],
    address: this.fb.group({ 
      street: [''],
      zip: ['']
    })
  })
}

In the parent component, simply forward the nested FormGroup:

<address [address]="myForm.get('address')"></address>

In the child component, use @Input for the nested FormGroup:

@Input() address: FormGroup;

In the template of the child component, bind the FormGroup using [formGroup]:

<div [formGroup]="address">
  <input formControlName="street">
  <input formControlName="zip">
</div>

If you prefer not to create a nested FormGroup, you can directly pass the parent form to the child. For example:

this.myForm = this.fb.group({
  name: [''],
  street: [''],
  zip: ['']
})

You have the flexibility to choose which controls to display in the child component. Following the previous example, if we only want to show street and zip, the child tag within the template would be:

<address [address]="myForm"></address>

Check out this

Demo demonstrating the first option, or explore the second Demo

For more insights on nested model-driven forms, visit this resource.

Answer 3

Answer №2

One way to achieve this functionality in template-driven forms is by utilizing ngModel. By adding the following code snippet to your component, you can inject the form of the parent component:

@Component({
viewProviders: [{ provide: ControlContainer, useExisting: NgForm}]
}) export class ChildComponent

It is important to ensure that each input field has a unique name. When using *ngFor to iterate over child components, make sure to include an index or another unique identifier in the name attribute, such as:

[name]="'address_' + i"

If you plan to organize your form into FormGroups, utilize ngModelGroup and

viewProviders: [{ provide: ControlContainer, useExisting: NgModelGroup }]

in place of ngForm. Additionally, add [ngModelGroup]="yourNameHere" to the HTML tags of certain child components.

Answer 4

One way to achieve this functionality in template-driven forms is by utilizing ngModel. By adding the following code snippet to your component, you can inject the form of the parent component:

@Component({
viewProviders: [{ provide: ControlContainer, useExisting: NgForm}]
}) export class ChildComponent

It is important to ensure that each input field has a unique name. When using *ngFor to iterate over child components, make sure to include an index or another unique identifier in the name attribute, such as:

[name]="'address_' + i"

If you plan to organize your form into FormGroups, utilize ngModelGroup and

viewProviders: [{ provide: ControlContainer, useExisting: NgModelGroup }]

in place of ngForm. Additionally, add [ngModelGroup]="yourNameHere" to the HTML tags of certain child components.

Answer 5

Answer №3

In my experience, creating a form field composition like this can be challenging with template-driven forms. The fields within your address component may not be properly registered in the form (NgForm.controls object), leading to issues with form validation.

One option is to develop a ControlValueAccessor component that accepts ngModel attribute along with all validations. However, displaying validation errors and managing changes can be complex since the address is treated as a single form field with intricate value.
Alternatively, you might consider passing the form reference into the Address component and registering the inner controls within it. While unconventional, this approach could potentially work (although not widely seen).
If feasible, transitioning to reactive forms from template-driven ones could provide a solution. By passing a form group object representing an address into the Address component, you can maintain the validation within your form definition. For a detailed example, refer to https://scotch.io/tutorials/how-to-build-nested-model-driven-forms-in-angular-2.

Answer 6

In my experience, creating a form field composition like this can be challenging with template-driven forms. The fields within your address component may not be properly registered in the form (NgForm.controls object), leading to issues with form validation.

One option is to develop a ControlValueAccessor component that accepts ngModel attribute along with all validations. However, displaying validation errors and managing changes can be complex since the address is treated as a single form field with intricate value.
Alternatively, you might consider passing the form reference into the Address component and registering the inner controls within it. While unconventional, this approach could potentially work (although not widely seen).
If feasible, transitioning to reactive forms from template-driven ones could provide a solution. By passing a form group object representing an address into the Address component, you can maintain the validation within your form definition. For a detailed example, refer to https://scotch.io/tutorials/how-to-build-nested-model-driven-forms-in-angular-2.

Answer 7

Answer №4

In the most recent releases of Angular 2+, it is now possible to divide your form into multiple components without needing to pass the formGroup instance to the child as an input.

To make this happen, you just need to import a specific provider into your child component:

viewProviders: [{provide: ControlContainer,useExisting: FormGroupDirective}]

Once you have done this, you can then access the main form by injecting the formGroupDirective in your child component like so:

constructor(private readonly formGroupDirective: FormGroupDirective)

Answer 8

In the most recent releases of Angular 2+, it is now possible to divide your form into multiple components without needing to pass the formGroup instance to the child as an input.

To make this happen, you just need to import a specific provider into your child component:

viewProviders: [{provide: ControlContainer,useExisting: FormGroupDirective}]

Once you have done this, you can then access the main form by injecting the formGroupDirective in your child component like so:

constructor(private readonly formGroupDirective: FormGroupDirective)

Answer 9

Answer №5

Here is a method that worked for me in a similar situation. I developed a directive called UseParentForm:

import { Directive } from '@angular/core';
import { ControlContainer, NgForm } from '@angular/forms';

@Directive({
  selector: '[appUseParentForm]',
  providers: [
    {
      provide: ControlContainer,
      useFactory: function (form: NgForm) {
        return form;
      },
      deps: [NgForm]
    }
  ]
})
export class UseParentFormDirective {
}

By using this directive on a child component like this:

<address app-use-parent-form></address>

The controls from AddressComponent will be included in form1. This means that the form validity will now also depend on the state of controls inside the child component.

This has been tested with Angular 6 only.

Answer 10

Here is a method that worked for me in a similar situation. I developed a directive called UseParentForm:

import { Directive } from '@angular/core';
import { ControlContainer, NgForm } from '@angular/forms';

@Directive({
  selector: '[appUseParentForm]',
  providers: [
    {
      provide: ControlContainer,
      useFactory: function (form: NgForm) {
        return form;
      },
      deps: [NgForm]
    }
  ]
})
export class UseParentFormDirective {
}

By using this directive on a child component like this:

<address app-use-parent-form></address>

The controls from AddressComponent will be included in form1. This means that the form validity will now also depend on the state of controls inside the child component.

This has been tested with Angular 6 only.

Answer 11

Answer №6

The top-rated response is quite common: I've encountered a project using this method and found it very difficult to manage.

A special thanks goes out to user @elia for their insightful contribution.

For added convenience, consider placing the provider in a constant:

import { Provider } from '@angular/core';
import { ControlContainer, FormGroupDirective } from '@angular/forms';

export const FormPart: Provider = {
  provide: ControlContainer,
  useExisting: FormGroupDirective,
};

In your desired component, simply import it like so:

@Component({
  ...
  viewProviders: [FormPart],
})

Add a directive with the aforementioned constructor code, which provides the parent form when necessary, allowing you to break down form logic into smaller sections.

I attempted to delve into how decorators work in Angular in order to extend @Component with a viewProvider, but it proved to be quite complex. It appears that it may not be possible, so I decided to abandon the idea. I would love to hear about others' experiences on this matter. Having such a feature supported by Angular would greatly simplify working with intricate forms.

Answer 12

The top-rated response is quite common: I've encountered a project using this method and found it very difficult to manage.

A special thanks goes out to user @elia for their insightful contribution.

For added convenience, consider placing the provider in a constant:

import { Provider } from '@angular/core';
import { ControlContainer, FormGroupDirective } from '@angular/forms';

export const FormPart: Provider = {
  provide: ControlContainer,
  useExisting: FormGroupDirective,
};

In your desired component, simply import it like so:

@Component({
  ...
  viewProviders: [FormPart],
})

Add a directive with the aforementioned constructor code, which provides the parent form when necessary, allowing you to break down form logic into smaller sections.

I attempted to delve into how decorators work in Angular in order to extend @Component with a viewProvider, but it proved to be quite complex. It appears that it may not be possible, so I decided to abandon the idea. I would love to hear about others' experiences on this matter. Having such a feature supported by Angular would greatly simplify working with intricate forms.

Breaking down a form into several sections for validation purposes

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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