Cannot read property 'id' of undefined on ngOnInit() Angular7

Question

I am beginner to angular. Problem is actually in EmployeeComponent.ts , if i call this.resetForm(); in ngOnInit() then the controls of dialog gets displayed during page load... but during edit when it comes from employeelist the service.formData sets back to null all time i don't want this to happen. I want both functionalities to happen.

This below error if i remove this.resetForm(); in ngOnInit() . (but edit works fine) Note : service.formData contains fields id, description and active

Consolelog error : EmployeeComponent_Host.ngfactory.js? [sm]:1 ERROR TypeError: Cannot read property 'id' of undefined at EmployeeComponent.push.

EmployeeComponent.ts

ngOnInit() {
  this.resetForm();
}


resetForm(form ? : NgForm) {

  if (form != null)
    form.resetForm();

  this.service.formData = {
    id: null,
    description: '',
    active: true,
  }
  console.log(this.service.formData.id);
}  

EmployeeListComponent.ts

onEdit(emp: Employee) {
  this.service.formData = Object.assign({}, emp);
  const dialogConfig = new MatDialogConfig();
  dialogConfig.disableClose = true;
  dialogConfig.autoFocus = true;
  dialogConfig.width = "50%";
  this.dialog.open(EmployeeComponent, dialogConfig);
}

Employee.component.html

<form #form="ngForm" autocomplete="off" >
  <mat-grid-list cols="2">
          <input type="hidden" name="id" #id="ngModel" [(ngModel)]="service.formData.id">       
        <mat-form-field>   
          <input name="description" matInput #description="ngModel" [(ngModel)]="service.formData.description" placeholder="Employee" required>  
   </mat-form-field>
 <mat-checkbox  matInput #active="ngModel" [(ngModel)]="service.formData.active" name="active">Active</mat-checkbox>         
  </mat-grid-list>
      <button mat-raised-button color="primary" type="submit" [disabled]="form.invalid" (click)="onSubmit(form)">Submit</button>
      <button mat-raised-button color="warn" style="margin-left: 6px;" (click)="onClear(form)">Clear</button>

</form>

Answer 1

Here EmployeeComponent is your mat dialog component to open so you need to provide data to the dialog using below in your constructor of EmployeeComponent

 constructor(
@Inject(MAT_DIALOG_DATA) data)){}

and when you open the dialog for editing purpose, you need to set data

  onEdit(emp: Employee) {
      dialogConfig = new MatDialogConfig();
      dialogConfig.disableClose = true;
      dialogConfig.autoFocus = true;
      dialogConfig.width = "50%";
      // Provide your data here      
      dialogConfig.data = emp;

      this.dialog.open(EmployeeComponent, dialogConfig);
    }

Now you can use this data on EmployeeComponent by name "data" property

and only use reset form in ngOninit

ngOnInit() {
if (form != null)
    form.resetForm();
}

Other things you need to handle like clear this data when you have done with save