嵌套表单组多次触发变更检测

Question

使用作为参考，我已经复制了使用反应式表单创建的动态嵌套表单组。

但在将新的表单组添加到表单数组时，它会多次触发更改检测。

my code

component.html

<button mat-flat-button color="primary" (click)="addMaterial()">Add</button>

<form [formGroup]="positionFormGroup" novalidate>
  <table formArrayName="positionInfos">

    <div *ngFor="let data of Controls.controls; let i = index">
      <div [formGroupName]="i">

        <input type="text" formControlName="idMaterial" [matAutocomplete]="materialAuto">
        <mat-autocomplete #materialAuto="matAutocomplete">
          <mat-option *ngFor="let option of materialFilteredOptions | async" [value]="option.description">
            {{option.description}}
          </mat-option>
        </mat-autocomplete>
      </div>
    </div>

  </table>
</form>

component.ts

export class AppComponent {
  positionFormGroup: FormGroup;
  materialControl: FormControl = new FormControl('');
  materialFilteredOptions: Observable<{ description: string; }[]>;
  options = [
    { description: 'item1' },
    { description: 'item2' },
    { description: 'item3' },
    { description: 'item4' }
  ]
  constructor(private formBuilder: FormBuilder) {
  }

  ngOnInit(): void {
    this.materialFilteredOptions = this.materialControl.valueChanges
      .pipe(
        startWith(''),
        map(value => this.options)
      );
    this.positionFormGroup = this.formBuilder.group({
      positionInfos: new FormArray([])
    });

    this.addMaterial();

  }

  ngDoCheck(){
    console.log('triggered');
  }

  addMaterial() {
    (this.positionFormGroup.get('positionInfos') as FormArray).push(this.formBuilder.group({
      rowID: '0',
      position: '0',
      idMaterial: 'item1',
      quantity: 1,
      isDeleted: false,
      isActive: true
    }));
  }

  confirm(){
    console.log( this.positionFormGroup.get('positionInfos').value)
  }

  get Controls(){
    console.log( (this.positionFormGroup.get('positionInfos') as FormArray));
    return (this.positionFormGroup.get('positionInfos') as FormArray);
     
  }
}

也共享了控制台。当我将新的表单组添加到表单数组时，它正在发生。我不明白为什么它会多次触发变化检测。

如果我遗漏了什么，请告诉我。提前致谢

Answer 1

我应该将 ChangeDetectionStrategy 更改为 onPush，这样组件只会渲染一次

@Component({
  selector: "hello",
  templateUrl: "./hello.component.html",
  changeDetection: ChangeDetectionStrategy.OnPush,
})

your working example

Answer 2

经过一番研究，我得到了答案。每当发生变化检测时，模板都会重新评估该方法。

不用控件getter，直接用class属性得到嵌套表单组控件

ts

  this.control = this.getControls().controls;

  getControls(){
    console.log( (this.positionFormGroup.get('positionInfos') as FormArray));
    return (this.positionFormGroup.get('positionInfos') as FormArray);
  }

html

    <div *ngFor="let data of control; let i = index">

嵌套表单组多次触发变更检测

Nested Form Group triggeres change detection multiple times

typescript

angular-reactive-forms

formarray

formgroups

angular9