Angular 中的 'missingFormException' 使用 Reactive forms？

Question

I'm getting some weird behavior which I don't know how to deal with.

I have a template which is one big form, but I'll show only single input filed where the errors is showing.

    <form [formGroup]="myForm" (ngSubmit)="submitForm()" class="row g-3 needs-validation" novalidate>

                <div class="col-md-4">
                  <label for="idCourse" class="form-label">ID</label>
                  
                  <input type="text" class="form-control" [value]="course['id']"  disabled id="idCourse" >
                </div>
    </form>

Now, in .ts file I'm basically fetching DTO from a service and initializing FormControl with bunch of FormGroups. They all work correct and map on the template as expected. But once I use service from backend I'm getting an error.

 initReactiveForm() {
            
        this.myForm = this.fb.group({
         // id:[this.course['id'],   [ ]], since this input field is disabled I'm not adding it to form, but I tried adding it as well, didn't do the job
          name:[this.course['name'], [Validators.required, Validators.minLength(3),  Validator.cannotContainWhitespaceOnly]],
    
        })
    
 }

Inside ngOnInit()

ngOnInit(): void {

    this.activatedRoute.paramMap.subscribe(params => {
      var courseId = params.get('courseIdPlaceholder');

      //some custom validation and simple checks...
    
      if (courseId) {
        

        //check in service layer if Course exists for given Id; this won't work
        this.firebaseService.getCourseById(courseId).subscribe(course => {

           this.course = course ;
           this.initReactiveForm();

        });

        //this.course = Builider(Course).id("1").build(); but this works if I comment out above code which fetches Course from service
       // this.initReactiveForm();

      } else {
        alert("Not valid id!")
        this.router.navigate(["/home"]);
        return;
      }

    });
    
  }

The error I'm getting looks like this:

    core.mjs:6485 ERROR Error: formGroup expects a FormGroup instance. Please pass one in.

      Example:

      
  <div [formGroup]="myGroup">
    <input formControlName="firstName">
  </div>

  In your class:

  this.myGroup = new FormGroup({
      firstName: new FormControl()
  });
    at missingFormException (forms.mjs:1494:12)
    at FormGroupDirective._checkFormPresent (forms.mjs:5523:19)
    at FormGroupDirective.ngOnChanges (forms.mjs:5296:14)
    at FormGroupDirective.rememberChangeHistoryAndInvokeOnChangesHook (core.mjs:1508:1)
    at callHook (core.mjs:2552:1)
    at callHooks (core.mjs:2511:1)
    at executeInitAndCheckHooks (core.mjs:2462:1)
    at selectIndexInternal (core.mjs:8405:1)
    at Module.ɵɵadvance (core.mjs:8388:1)
at CourseComponent_Template (course.component.html:9:59)

Line course.component.html:9:59 points at the beginning of [value]="course['id'] in the template.

If I don't use firebaseService and just hardcode a object, this.course = Builider(Course).id("1").build(); then, form populates and everything works and no error in console.

Here is the service:

public getAllCourses() : Observable<Course[]>{
    return this.fireDb.list<Course>('courses').valueChanges();
   
}

I'm actually fetching all the courses from Firebase and in subscribe() I take the first Course. Everything is console.log -ed and I have values I want. But somehow the template renders before I get the object.

Just to be clear, my form does in fact gets populated, but I'm getting this error which annoys me so much.

Answer 1

Since you're initializing the myForm FromGroup synchronously within the subscribe of the paramMap and getCourseById , then the component template won't be able (while the initialization) to recognize the myForm instance which is null before initializing it in the initReactiveForm method.

I think to resolve this issue you either need to:

• Add *ngIf="myForm" , to render the form element only after initializing the myForm .
• OR initialize the myForm directly within the ngOnInit , then you can patchValue to it once the data comes from the getCourseById .