How can we dynamically enable or disable a button based on the availability of input field data in an Angular FormGroup?

When it comes to deciding whether my form input field is required or not, I rely on the API data set. If the input is mandatory, I want to disable the button until the user inputs some value. As an absolute beginner in reactive form in angular, I could really use some expert guidance on how to achieve this.

------------HTML----------------------

 <div class="a">
      <at-card *ngIf="selectedId$|async" class="b">
        <at-detail [selectedDetail]="selectedDetailModel$|async">
        </at-detail>
        <div [formGroup]="DetailForm" class="grid grid-columns-2">
          <br />
          <mat-form-field>
            <mat-label>Comment</mat-label>
            <input matInput formControlName="comment" [type]="'text'" [required]="commentRequired">
          </mat-form-field>
        </div>
      </at-card>
      <at-sticky-footer>
        <button *ngIf="selectedId$|async" (click)="onSubmit()">submit</button>
      </at-sticky-footer> 
</div>

------------------component.ts------------------

commentRequired: boolean;

DetailForm = new FormGroup({ comment: new FormControl(), rate: new FormControl() });

ngOnInit(): void {
   inputCommentIsMandatory:boolean = <retrieve API data about whether entering a comment is required or not>
         
   //Based on the API data, mark the comment field as required
   //Check if user input is needed for the comment field
   //If it is required, check if there is user input in the comment field -> 
   //Enable the button if there is, otherwise disable it
   if(inputCommentIsMandatory){
    this.commentRequired = true;
    //Enable the button when user enters data, disable it if the input field is empty
    }else{
    //Button always enabled (whether comment is entered or not)
    this.commentRequired = false;
    }
 
  }

------------------latest update (button always disable, even if comment is not mandatory ------------------------------------

I have updated the code as follows.

isCommentMandatory(Reviews: ReviewModel[]): void {
  

      if (Reviews.length > 0) {
          console.log("called ...1 ");
          this.isCommentRequired = false;
          this.DetailForm = this.fb.group({
            comment: [''],
            rate: ['']
          });
        } else {
          console.log("called ...2 ");
          this.isCommentRequired = true;
          this.DetailForm = this.fb.group({
            comment: ['', Validators.required],
            rate: ['']
          });
        }
      }

and called it like this,

ngOnInit(): void {
  
       this.DetailModel$.pipe().subscribe((opd => {
          this.detail = opd as Detail;
          const date = this.detail?.time;
          const planDate = date !== undefined ? date : new Date();
          //Select reviews data based on the date
          this.store.select(selectAllReviewsDetailsModel(planDate)).
            subscribe(res => this.Reviews = res);
    
          //Need to call after changing Details
          this.isCommentMandatory(this.Reviews);
        }));
      }

In the HTML template, it is bound as below,

 <at-sticky-footer>
        <button *ngIf="selectedId$|async" [disabled]="!(DetailModel.valid && (DetailModel.dirty))" (click)="submit()">submit</button>
      </at-sticky-footer>

However, now in both scenarios, something needs to be typed in to enable the button.

Answer №1

When working with reactive forms, the key concept is the one-way data flow. Data originates from the component and flows to the template. Once the user interacts with the data and clicks "save," control is handed back to the component.

Any data validation or conditional logic that alters the data should be handled within the component. However, behavioral changes that do not affect the data or validation can be implemented in the template as a directive. For example, displaying a visual indicator like "this row changed" can be achieved through a template directive.

All form controls in your form are Observables, allowing you to monitor changes and take appropriate actions in the component. However, for simpler use cases, setting up the form logic during initialization is sufficient. It is advisable to delay building the form until the Http.GET operation returns, as it is an asynchronous event. This involves placing the form-building logic inside the closure for the http call.

Save Button Configuration:

For the save button functionality, consider using the following code snippet:

<button [disabled]="!(DetailForm.touched && DetailForm.valid)">

This code snippet assumes that DetailForm represents the base FormGroup.

The comment form control should include a [Validator.Required] in its definition:

 this.DetailForm= this.fb.group({
      comment: ['', Validators.required]
  });

It is also possible to create a Custom Validation while setting up the form and retrieving initial data from the server to determine if the comment field should be mandatory.

Organizing the Form Group and Form Builder:

Based on your recent update, here is a suggested structure for the component.ts:

constructor(private fb: FormBuilder) { }
DetailForm: FormGroup;

ngOnInit(): void {
   const dataAvailable = //this.http.get<boolean>(s =>  s);
   if (dataAvailable) {
     this.DetailForm = this.fb.group({ 
      comment: ['', Validators.Required]
     });
   }
   else {
     this.DetailForm = this.fb.group({ 
      comment: [''];
     })
   }
  }
   

component.html

<div class="a">
      <at-card *ngIf="selectedId$|async" class="b">
        <at-detail [selectedDetail]="selectedDetailModel$|async">
        </at-detail>
        <div [formGroup]="DetailForm" class="grid grid-columns-2">
          <br />
          <mat-form-field>
            <mat-label>Comment</mat-label>
            <input matInput formControlName="comment" [type]="'text'">
          </mat-form-field>
        </div>
      </at-card>
      <at-sticky-footer>
        <button [disabled]="!(DetailForm.valid && (DetailForm.touched || DetailForm.dirty)" (click)="onSubmit()">submit</button>
      </at-sticky-footer> 
</div>

Understanding touched and blurred:

touched: Indicates the control has been interacted with, changed, and blurred; dirty: Indicates the control has been interacted with, changed, but not yet blurred.

Choosing between touched and dirty depends on the specific use case.

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