Passing value from parent component to child component by reference

Question

I have 2 components: parentComponent and childComponent. In parentComponent I have a FormGroup type value as parentForm that is passed to childComponent via @input:

export class parentComponent {
...

 parentForm: FormGroup;

....
}

export class childComponent {
...

 @Input()
 childForm :FormGroup; //The parentForm 

....
}

when I run these codes everything is ok and my childComponent recognize the childForm which is an input value from parentComponent but whenever I change some properties in parentForm in parentComponent the childComponent is not able to be aware of these changes and when I debug my codes I see that the childComponent holds old input value and the changes is not updated in childForm in childComponent. now I seek to find a way to pass the reference of parentForm to solve my problem. because I think by this way any change in the parentForm will inform childForm immediately. I do not know how it is possible. (the version of Angular is 5.0.1)

stackblitz.com/edit/angular-lk4j8t : I don't know what behavior you're looking for but I definitely get the changes to the childForm as well. Take a look at this stackblitz. You can try do this.childForm.valueChanges on your childComponent as well. — Chau Tran
– Chau Tran, Commented Dec 22, 2017 at 23:33

JTejedor · Accepted Answer · 2017-12-22 23:30:31Z

0

In essence, this question is very related with this question and this another question.

To solve your problem, I suggest this approach:

Fill an object using using your form group with the directive NgModel.
Change @Input() childForm :FormGroup for @Input() childForm : Object being Object the filled object class using NgModel
If Object is not a primitive value string,boolean, num, it will be passed by reference so you will have the updated value immediately.

answered Dec 22, 2017 at 23:30

JTejedor

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