CODEWITHSUNDEEP
angularangular2-formsangular2-formbuilder
ebakunin
ebakunin

Reputation: 3791

Two way binding in reactive forms

Using Angular 2, two-way binding is easy in template-driven forms - you just use the banana box syntax. How would you replicate this behavior in a model-driven form?

For example, here is a standard reactive form. Let's pretend it's much more complicated than it looks, with lots and lots of various inputs and business logic, and therefore more appropriate for a model-driven approach than a template-driven approach.

    export class ExampleModel {
        public name: string;
        // ... lots of other inputs
    }

    @Component({
        template: `
            <form [formGroup]="form">
                <input type="text" formControlName="name">
                ... lots of other inputs
            </form>

            <h4>Example values: {{example | json}}</h4>
        `
    })
    export class ExampleComponent {
        public form: FormGroup;
        public example: ExampleModel = new ExampleModel();

        constructor(private _fb: FormBuilder) {
            this.form = this._fb.group({
                name: [ this.example.name, Validators.required ]
                // lots of other inputs
            });
        }

        this.form.valueChanges.subscribe({
            form => {
                console.info('form values', form);
            }
        });
    }

In the subscribe() I can apply all sorts of logic to the form values and map them as necessary. However, I don't want to map every input value from the form. I just want to see the values for the entire employee model as it updates, in a approach similar to [(ngModel)]="example.name", and as displayed in the json pipe in the template. How can I accomplish this?

Upvotes: 94

Views: 173353

Answers (9)

Shiba Shill
Shiba Shill

Reputation: 1

Do not use ng model in reactive form cause it is deprecated. Suppose if you have html control which is not a part of form group, we can use simple includeinactive = new formControl() in ts file and html inside form in html control we can use [formControl] = includeinactive. If we want to disable update value we can use patchvalue or setvalue to update it. It will not log any error or warnings in developers tool console also.

Upvotes: 0

Eamanpreet Singh
Eamanpreet Singh

Reputation: 11

You can achieve two way binding by using Reactive forms

constructor(private fb: FormBuilder)

this.formData= fb.group({
        variable: new FormControl(value,Validators.required)
      })
      
      //the 'value' attribute carries the value you want to bind
var value="Eamanpreet Singh"

<form [formGroup]="formData" (ngSubmit)="submit();">
      <mat-form-field>
            <input matInput placeholder="Name" formControlName="variable">
      </mat-form-field>

Upvotes: 0

kneeki
kneeki

Reputation: 2692

An Angular 6+ solution...

I too would like reactive form validation while also using two-way data binding. The best solution I've come up with was to hook the form group's valueChanges event with a debounce timer to update the model. Here's an example:

<form [formGroup]="form">
  <input class="form-control" type="date" name="myDate" formControlName="myDate">
</form>

public myModel = {
  myDate: '2021-01-27'
};

public form = this.builder.group({
  myDate: [this.myModel.myDate, [Validators.required]],
});

// Don't update the model with every keypress, instead wait 1s and then update
this.form.valueChanges.pipe(debounceTime(1000)).subscribe((changes) => {
  for (let key of Object.keys(changes)) {
    this.myModel[key] = values[key];
  }
});

To better help copy/pasta I'm going to update the value of all properties of the moodel with the given changes. If you only wanted to update one property with two-way data binding you should use something like:

this.form.get('myDate').valueChanges.pipe(debounceTime(1000)).subscribe((changes) => {
  this.myModel.myDate = changes.myDate;
});

Upvotes: 6

Paul Samsotha
Paul Samsotha

Reputation: 208944

Note: as mentioned by @Clouse24, "Using Reactive Froms with ngModel is deprecated in angular 6 and will be removed in a future version of Angular" (which means that the answer below will no longer be supported in the future). Please read the link to see the reasoning for deprecation and to see what alternatives you will have.

You can use [(ngModel)] with Reactive forms.

template

<form [formGroup]="form">
  <input name="first" formControlName="first" [(ngModel)]="example.first"/>
  <input name="last" formControlName="last" [(ngModel)]="example.last"/>
</form>

component

export class App {
  form: FormGroup;
  example = { first: "", last: "" };

  constructor(builder: FormBuilder) {
    this.form = builder.group({
      first: "",
      last: ""
    });
  }
}

Plunker

This will a completely different directive than the one that would be used without the formControlName. With reactive forms, it will be the FormControlNameDirective. Without the formControlName, the NgModel directive would be used.

Upvotes: 81

Matheus Bueno
Matheus Bueno

Reputation: 21

If you just want to show a input value just create a variable in your input and use in your template.

<form [formGroup]="form">
  <input type="text" formControlName="name" #name>
  ... lots of other inputs
</form>

<h4>Example values: {{ name.value }}</h4>

Upvotes: 2

Vedran
Vedran

Reputation: 11029

    // Allow two way binding on the [(name)] from the parent component
    private nameValue: string;
    @Input()
    get name() {
        return this.nameValue;
    }
    set name(values) {
        this.nameValue = values;
        this.nameChange.emit(this.nameValue);
    }
    @Output() nameChange = new EventEmitter<string>();

    ngOnInit() {
        // Update local value and notify parent on control value change
        this.formControl.valueChanges.forEach(value => this.name = value));
    }

    ngOnChanges() {
        // Update local value on parent change
        this.formControl.setValue(this.expression);
    }

Upvotes: 4

Alexander Gharibashvili
Alexander Gharibashvili

Reputation: 983

ngModel or Template driven forms and reactive forms( model driven forms ) can be mixed together. for example, it's easy to read data without subscription when you use TDF and on the other hand, you can provide some validations using MDF. But i would prefer to choose only one of them.

The biggest disadvantage of TDF is that you can't apply unit tests on them and on the other hand it's much dirtier the template when you use TDF.

Upvotes: 0

Andre Elrico
Andre Elrico

Reputation: 11480

Here is how you can solve it:

In order to have the result of two-way-binding

I use local "template variables" and use the same formControl for both fields.

<form [formGroup]="formGroup">
  <input #myInput (input)="mySlider.value = myInput.value" type="number" formControlName="twoWayControl">

  <mat-slider #mySlider (input)="myInput.value = mySlider.value" formControlName="twoWayControl" min="1" max="100">
  </mat-slider>

</form>

When I programmatically want to change the value of the model I use setValue() as others have proclaimed.

setTo33() {
  this.formGroup.get('twoWayControl').setValue(33);
}

Upvotes: 17

Jens Alenius
Jens Alenius

Reputation: 1931

Sometimes you might need to combine [(ngModel)] with Reactive forms. I could be some inputcontrol that you don't need as a part of the form, but you still need it to be binded to the controller. Then you can use: [(ngModel)]="something" [ngModelOptions]="{standalone: true}"

Upvotes: 24

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