Bidirectional data binding in model-driven forms

Question

Bidirectional data binding in model-driven forms

Currently, I am working on a reactive form that includes fields for first name, last name, and display name. The goal is for the display name to automatically populate with the concatenated values of the first and last name. However, as I am still learning, I have been struggling to identify the issue in my code. Any guidance or advice would be greatly appreciated. Thank you.

Below is the code I have so far:


  <form [formGroup]="myForm" novalidate (ngSubmit)="save(myForm.value, myForm.valid)">
    <div class="form-group">
      <label for="">First Name</label>
      <input type="text" class="form-control" formControlName="firstname" [(ngModel)]="firstname">
    </div>
    <div class="form-group">
      <label for="">Last Name</label>
      <input type="text" class="form-control" formControlName="lastname" [(ngModel)]="secondnamename">
    </div>
    <div class="form-group">
      <label for="">Display Name</label>
      <input type="text" class="form-control" formControlName="displayname" value='{{firstname}}{{lastname}}'>
    </div>
    <div class="margin-20">
      <div>myForm details:-</div>
      <pre>myForm value: <br>{{myForm.value | json}}</pre>
    </div>
  </form>

Link to my Plunker

Gif:

https://i.sstatic.net/n4KxG.gif

angular typescript

Answer 1

Answer №1

If you prefer a more "reactive" approach, you can listen to changes of the form using the following code snippet:

   this.myForm.valueChanges.subscribe((form) => {
     this.displayname = `${form.firstname} ${form.secondname}`;
   });

This method allows you to eliminate the need for two-way data-binding and local state for firstname and secondname. Check out the Plunker example here: https://plnkr.co/edit/h5aFRDTWfj0gQ69CvVK7?p=preview

Answer 2

If you prefer a more "reactive" approach, you can listen to changes of the form using the following code snippet:

   this.myForm.valueChanges.subscribe((form) => {
     this.displayname = `${form.firstname} ${form.secondname}`;
   });

This method allows you to eliminate the need for two-way data-binding and local state for firstname and secondname. Check out the Plunker example here: https://plnkr.co/edit/h5aFRDTWfj0gQ69CvVK7?p=preview

Answer 3

Answer №2

To achieve the desired functionality, you can follow this example (referencing: https://angular.io/docs/ts/latest/guide/user-input.html)

Update your template as shown below:

<div class="form-group">
  <label for="">First Name</label>
  <input type="text" class="form-control" formControlName="firstname" [(ngModel)]="firstname" (keyup)="onKey($event)">
</div>
<div class="form-group">
  <label for="">Last Name</label>
  <input type="text" class="form-control" formControlName="lastname" [(ngModel)]="secondname" (keyup)="onKey($event)">
</div>
<div class="form-group">
  <label for="">Display Name</label>
  <input type="text" class="form-control" formControlName="displayname" value='{{displayname}}'>
</div>

Then, update your component.ts file with the following function:

onKey(event:any) { 
displayname = firstname + ' ' + secondnamename;
}

Answer 4

To achieve the desired functionality, you can follow this example (referencing: https://angular.io/docs/ts/latest/guide/user-input.html)

Update your template as shown below:

<div class="form-group">
  <label for="">First Name</label>
  <input type="text" class="form-control" formControlName="firstname" [(ngModel)]="firstname" (keyup)="onKey($event)">
</div>
<div class="form-group">
  <label for="">Last Name</label>
  <input type="text" class="form-control" formControlName="lastname" [(ngModel)]="secondname" (keyup)="onKey($event)">
</div>
<div class="form-group">
  <label for="">Display Name</label>
  <input type="text" class="form-control" formControlName="displayname" value='{{displayname}}'>
</div>

Then, update your component.ts file with the following function:

onKey(event:any) { 
displayname = firstname + ' ' + secondnamename;
}

Answer 5

Answer №3

Issue with Display Name not updating after the second name change:

The reason for this issue is a typo in your code - you should use the model value instead of formControlName. Please refer to the updated code on Plunker.

 <form [formGroup]="myForm" novalidate (ngSubmit)="save(myForm.value, myForm.valid)">
    <div class="form-group">
      <label for="">First Name</label>
      <input type="text" class="form-control" formControlName="firstname" [(ngModel)]="firstname">
    </div>
    <div class="form-group">
      <label for="">Last Name</label>
      <input type="text" class="form-control" formControlName="lastname" [(ngModel)]="secondnamename">
    </div>
    <div class="form-group">
      <label for="">Display Name</label>
      <input type="text" class="form-control" formControlName="displayname" value='{{firstname}} {{secondnamename}}'> //change in this line
    </div>
    <div class="margin-20">
      <div>myForm details:-</div>
      <pre>myForm value: <br>{{myForm.value | json}}</pre>
    </div>
  </form>

To update the form value for 'Display Name', you need to trigger an event like:

this.element.nativeElement.dispatchEvent(new Event('input'));

Or any other appropriate events (onBlur, onClick, onFocus) for the first two text boxes in the component.

Answer 6

Issue with Display Name not updating after the second name change:

The reason for this issue is a typo in your code - you should use the model value instead of formControlName. Please refer to the updated code on Plunker.

 <form [formGroup]="myForm" novalidate (ngSubmit)="save(myForm.value, myForm.valid)">
    <div class="form-group">
      <label for="">First Name</label>
      <input type="text" class="form-control" formControlName="firstname" [(ngModel)]="firstname">
    </div>
    <div class="form-group">
      <label for="">Last Name</label>
      <input type="text" class="form-control" formControlName="lastname" [(ngModel)]="secondnamename">
    </div>
    <div class="form-group">
      <label for="">Display Name</label>
      <input type="text" class="form-control" formControlName="displayname" value='{{firstname}} {{secondnamename}}'> //change in this line
    </div>
    <div class="margin-20">
      <div>myForm details:-</div>
      <pre>myForm value: <br>{{myForm.value | json}}</pre>
    </div>
  </form>

To update the form value for 'Display Name', you need to trigger an event like:

this.element.nativeElement.dispatchEvent(new Event('input'));

Or any other appropriate events (onBlur, onClick, onFocus) for the first two text boxes in the component.

Answer 7

Answer №4

To modify your display name input, follow these steps:

 <input type="text" class="form-control" formControlName="displayname" [ngModel]=firstname+secondname>

This setup enables one-way binding between the inputs of firstname and secondname.

The next step involves updating your app.component.ts file as shown below:

firstname:string = '';
secondname:string = '';

Simply insert an empty string for both variables to complete the process.

Answer 8

To modify your display name input, follow these steps:

 <input type="text" class="form-control" formControlName="displayname" [ngModel]=firstname+secondname>

This setup enables one-way binding between the inputs of firstname and secondname.

The next step involves updating your app.component.ts file as shown below:

firstname:string = '';
secondname:string = '';

Simply insert an empty string for both variables to complete the process.

Answer 9

Answer №5

The information provided back in 2016 is now outdated, according to the Angular API documentation. The use of ngModel with reactive form directives has been deprecated starting from Angular v6 and will be removed in a future version.

Deprecated Usage of ngModel with Reactive Forms

It is recommended to follow reactive forms patterns going forward as outlined in the deprecation guide.

In this context, it is best practice to utilize reactive forms like so:

<input [formControl]="control">

in the template, and set the value within the component model using:

this.control.setValue('some value');

Instead of directly using the line:

<input type="text" class="form-control" formControlName="displayname">

You would create a FormControl object, likely named dname, and connect it accordingly:

<input type="text" class="form-control" [formControl]="dname">

To update the value of this control in the component model, you can use:

this.dname.setValue(this.fname.value + this.lname.value)

This action should be triggered on the desired event for changing the display name control, such as the subscriber function linked to the value change observable for the first and last name controls. For clarity purposes, let's assume these controls are named fname and lname respectively within the component model.

Answer 10

The information provided back in 2016 is now outdated, according to the Angular API documentation. The use of ngModel with reactive form directives has been deprecated starting from Angular v6 and will be removed in a future version.

Deprecated Usage of ngModel with Reactive Forms

It is recommended to follow reactive forms patterns going forward as outlined in the deprecation guide.

In this context, it is best practice to utilize reactive forms like so:

<input [formControl]="control">

in the template, and set the value within the component model using:

this.control.setValue('some value');

Instead of directly using the line:

<input type="text" class="form-control" formControlName="displayname">

You would create a FormControl object, likely named dname, and connect it accordingly:

<input type="text" class="form-control" [formControl]="dname">

To update the value of this control in the component model, you can use:

this.dname.setValue(this.fname.value + this.lname.value)

This action should be triggered on the desired event for changing the display name control, such as the subscriber function linked to the value change observable for the first and last name controls. For clarity purposes, let's assume these controls are named fname and lname respectively within the component model.

Bidirectional data binding in model-driven forms

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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