Angular FormArray valueChanges更改后执行多​​次

Question

我有一个带有FormAwway的表格，其中显示了所购买产品的内容，这是我的组成部分：

constructor() {
    this.purchaseForm = new FormGroup({
        id: new FormControl(null, Validators.required),
        purchase: new FormControl(null, Validators.required),
        date: new FormControl(null, Validators.required),
        products: new FormArray([]),
    });
}

public createNewLine(object: any = {}): FormGroup {
    const newLine = new FormGroup({
      index: new FormControl(null),
      id: new FormControl(object.id, Validators.required),
      id_product: new FormControl(object.id_produto, Validators.required),
      quantity: new FormControl(object.quantidade, Validators.required),
      value_unit: new FormControl(object.valor_unitario, Validators.required),
      value_total: new FormControl(object.valor_total, Validators.required),
    });

    const formArray = <FormArray>this.purchaseForm.get('products');
    newLine.get('index').patchValue(formArray.length);
    newLine.valueChanges.pipe(debounceTime(400)).subscribe(value => this.updateProductValue(value));

    return newLine;
}

private updateProductValue(object): void {
    const quantity = parseFloat(object.quantity);
    const value_total = parseFloat(object.value_total);
    const formArray = this.purchaseForm.controls['products'] as FormArray;

    object.value_unit = value_total / quantity;
    formArray.at(object.index).patchValue(object);
}

当我用数量或总价值更改输入时，我需要更新该特定产品的单位价值。问题在于，当我进行计算并更新值时，它将检测为新的值更改并再次执行该函数，直到创建一个循环。

我在这里做错了什么？或者我需要采取什么措施来防止这种行为？除了此循环外，其他所有功能都按预期运行。

Answer 1

尝试像这样更改最后一行：

formArray.at(object.index).patchValue(object, { emitEvent: false, onlySelf: true });