Disable a field in angular reactive form

Question

In my angular 6 application, i am making a reactive form which has,

Html

<form [formGroup]="form">

    <h2>Click the add button below</h2>
    <button (click)="addCreds()">Add</button>
    <div formArrayName="credentials" >
      <div *ngFor="let creds of form.get('credentials').controls; let i = index" 
          [formGroupName]="i" style="display: flex">
          <select formControlName="action">
             <option *ngFor="let option of options" value="{{option.key}}">
               {{option.value}} 
             </option>
          </select>
          <input placeholder="Name" formControlName="name">
<div *ngIf="creds.value.action=='set' ||
      creds.value.action=='go'">
                   <input placeholder="Label" formControlName="label">
          </div>
      </div>
    </div>
    </form>

Here i have used

<div *ngIf="creds.value.action=='set' || creds.value.action=='go'"> <input placeholder="Label" formControlName="label"> </div>

which will display the field label if the condition is true or else it will not be displayed.

But i need to only disable that field and should not remove it completely..

For which i have tried,

<input [disabled]="creds.value.action != 'set' || creds.value.action != 'go' " placeholder="Label" formControlName="label">

But it doesn't works.

Stackblitz with *ngIf https://stackblitz.com/edit/angular-form-array-example-25y1ix

Stackblitz with disabled https://stackblitz.com/edit/angular-form-array-example-laftgu

Kindly help me how to disable the label field if the selected action (first dropdown) value is wait ..

Answer 1

Just create a CSS class:

.disabled {
  pointer-events:none;
  background-color: #D3D3D3;
}

Add a method to your Component:

getValueByIndex(index) {
  const actionValue = ( < FormArray > this.form.get('credentials')).at(index).value.action;
  return actionValue !== 'set' && actionValue !== 'go';
}

Use this method in your template:

<input 
    [class.disabled]="getValueByIndex(i)" 
    placeholder="Label" 
    formControlName="label">

---

Here's a Working Sample StackBlitz for your ref.

---

UPDATE:

Alternatively, you can do the following:

Make the label field disabled by default:

addCreds() {
  const creds = this.form.controls.credentials as FormArray;
  creds.push(this.fb.group({
    action: '',
    name: '',
    label: {
      value: '',
      disabled: true
    },
    state: 'na'
  }));
}

And then listen to the (ngModelChange) event on the form to update the state of the label field:

<select 
  formControlName="action"
  (ngModelChange)="($event === 'set' || $event === 'go') ? creds.controls.label.enable() : creds.controls.label.disable()">
  <option 
    *ngFor="let option of data" 
    [value]="option.key">
    {{option.value}} 
  </option>
</select>

---

Here's a Working Sample StackBlitz for this approach.

---

Thanks to A.Winnen for his comments on the performance implications of using the previous approach.

Answer 2

In Reactive Form you cannot use the disabled directive. Instead, you'll need to disable the formControl the 'reactive way' by calling enable() or disable() function.

addCreds() {
    const creds = this.form.controls.credentials as FormArray;
    const newGroup = this.fb.group({
      action: '',
      name: '',
      label: ''
    });
    newGroup.controls.action.valueChanges.subscribe((currentAction) => {
      if (typeof currentAction === "string" && currentAction.toLowerCase() === 'wait') {
        newGroup.controls.label.disable();
      } else {
        newGroup.controls.label.enable();
      }
    });
    creds.push(newGroup);
  }

I modified your stackblitz example: https://stackblitz.com/edit/angular-form-array-example-ymysw4