Using Angular 2's ngModel directive to bind a value passed in from an

Question

Using Angular 2's ngModel directive to bind a value passed in from an

Using [(ngModel)] in my child component with a string passed from the parent via @Input() is causing some issues.

Although the string is successfully passed from the parent to the child, any changes made to it within the child component do not reflect back to the parent's value.

I am confused about what might be missing or causing this problem.

Parent Component:

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [(value)]="name"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyValue';
  constructor() {

  }
}

Child Component:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>My custom input</p>
      <textarea [(ngModel)]="value"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;

  constructor() {

  }
}

A Plnkr example demonstrating the issue can be found here: https://plnkr.co/edit/jCF5kt73P38EFYUAZF6l

angular typescript angular2-forms

Answer 1

Answer №1

If you want to implement a feature that notifies about changes, consider adding an output element:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>Input Field:</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>()

  update(value) {
    this.valueChange.emit(value);
  }

  constructor() {

  }
}

Answer 2

If you want to implement a feature that notifies about changes, consider adding an output element:

import {Component, Input} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
    <p>Input Field:</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>()

  update(value) {
    this.valueChange.emit(value);
  }

  constructor() {

  }
}

Answer 3

Answer №2

Indeed, the @Input directive operates in a singular direction. It allows for communication from parent to child by notifying the child component of any changes made by the parent. Conversely, the parent component remains oblivious to any alterations within the child component when exclusively utilizing @Input.

Answer 4

Indeed, the @Input directive operates in a singular direction. It allows for communication from parent to child by notifying the child component of any changes made by the parent. Conversely, the parent component remains oblivious to any alterations within the child component when exclusively utilizing @Input.

Answer 5

Answer №3

Building upon the response from @Günter Zöchbauer, I have made some changes to the app.ts file.

Here is the updated app.ts code:

// Main app component
import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {Child} from './child'
import {FormsModule} from "@angular/forms";

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [value]="name" (valueChange)="updateValue($event)"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyUpdatedValue';
  constructor() {

  }
  
  updateValue(value){
      this.name = value;
    }
}

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App, Child ],
  bootstrap: [ App ]
})
export class AppModule {}

And here is the Child component:

import {Component, Input, Output, EventEmitter} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
      <p>My customized input</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>();

  constructor() {

  }

  update(value) {
    this.valueChange.emit(value);
  }
}

Answer 6

Building upon the response from @Günter Zöchbauer, I have made some changes to the app.ts file.

Here is the updated app.ts code:

// Main app component
import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {Child} from './child'
import {FormsModule} from "@angular/forms";

@Component({
  selector: 'my-app',
  template: `
    <div>
      <child [value]="name" (valueChange)="updateValue($event)"></child>
      <p>{{name}}</p>
    </div>
  `,
})
export class App {
  name:string = 'MyUpdatedValue';
  constructor() {

  }
  
  updateValue(value){
      this.name = value;
    }
}

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App, Child ],
  bootstrap: [ App ]
})
export class AppModule {}

And here is the Child component:

import {Component, Input, Output, EventEmitter} from '@angular/core'

@Component({
  selector: 'child',
  template: `
    <div>
      <p>My customized input</p>
      <textarea [(ngModel)]="value" (ngModelChange)="update($event)"></textarea>
    </div>
  `,
})
export class Child {


  @Input() value:string;
  @Output() valueChange:EventEmitter<string> = new EventEmitter<String>();

  constructor() {

  }

  update(value) {
    this.valueChange.emit(value);
  }
}

Using Angular 2's ngModel directive to bind a value passed in from an

Answer №1

Answer №2

Answer №3

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