Angular 2 Checkbox Two Way Data Binding

I´m fairly new to Angular2 and I have a little problem:

In my Login-Component-HTML, I have two checkboxes, which I want to bind in two way data-binding to the Login-Component-TypeScript.

This is the HTML:

<div class="checkbox">
<label>
    <input #saveUsername [(ngModel)]="saveUsername.selected" type="checkbox" data-toggle="toggle">Save username
</label>
</div>

And this is the Component.ts:

import { Component, OnInit }    from '@angular/core';
import { Router }               from '@angular/router';
import { Variables }            from '../../services/variables';

@Component({
    selector: 'login',
    moduleId: module.id,
    templateUrl: 'login.component.html',
    styleUrls: ['login.component.css']
})


export class LoginComponent implements OnInit {

    private saveUsername: boolean = true;
    private autoLogin: boolean = true;
    constructor(private router: Router, private variables: Variables) { }

    ngOnInit() { 
        this.loginValid = false;
        // Get user name from local storage if you want to save

        if (window.localStorage.getItem("username") === null) {
           this.saveUsername = true;
           this.autoLogin = true;
           console.log(this.saveUsername, this.autoLogin);
        } else {
           console.log("init", window.localStorage.getItem("username"));
        }
    }

    login(username: string, password: string, saveUsername: boolean, autoLogin: boolean) {
        this.variables.setUsername(username);
        this.variables.setPassword(password);
        this.variables.setIsLoggedIn(true);
        console.log(saveUsername, autoLogin);
        //this.router.navigate(['dashboard']);
    }

If I click an checkbox, I get the correct value in the controller (component).

But if I change the value of for example saveUsername in the component, the checkbox didn't "get" the new value.

So I can´t manipulate the checkbox from the Component (like I want to do in the ngOnInit in the component.

Thanks for your help!

You can remove .selected from saveUsername in your checkbox input since saveUsername is a boolean. Instead of [(ngModel)] use [checked]="saveUsername" (change)="saveUsername = !saveUsername"

Edit: Correct Solution:

<input
  type="checkbox"
  [checked]="saveUsername"
  (change)="saveUsername = !saveUsername"/>

Update: Like @newman noticed when ngModel is used in a form it won't work. However, you should use [ngModelOptions] attribute like (tested in Angular 7):

<input
  type="checkbox"
  [(ngModel)]="saveUsername"
  [ngModelOptions]="{standalone: true}"/> `

I also created an example at Stackblitz: https://stackblitz.com/edit/angular-abelrm

Unfortunately solution provided by @hakani is not two-way binding. It just handles One-way changing model from UI/FrontEnd part.

Instead the simple:

<input [(ngModel)]="checkboxFlag" type="checkbox"/>

will do two-way binding for checkbox.

Afterwards, when Model checkboxFlag is changed from Backend or UI part - voila, checkboxFlag stores actual checkbox state.

To be sure I've prepared Plunker code to present the result : https://plnkr.co/edit/OdEAPWRoqaj0T6Yp0Mfk

Just to complete this answer you should include the import { FormsModule } from '@angular/forms' into app.module.ts and add to imports array i.e

import { FormsModule } from '@angular/forms';

[...]

@NgModule({
  imports: [
    [...]
    FormsModule
  ],
  [...]
})

I'm working with Angular5 and I had to add the "name" attribute to get the binding to work... The "id" is not required for binding.

<input type="checkbox" id="rememberMe" name="rememberMe" [(ngModel)]="rememberMe">

I prefer something more explicit:

component.html

<input #saveUserNameCheckBox
    id="saveUserNameCheckBox" 
    type="checkbox" 
    [checked]="saveUsername" 
    (change)="onSaveUsernameChanged(saveUserNameCheckBox.checked)" />

component.ts

public saveUsername:boolean;

public onSaveUsernameChanged(value:boolean){
    this.saveUsername = value;
}

You can just use something like this to have two way data binding:

<input type="checkbox" [checked]="model.property" (change)="model.property = !model.consent_obtained_ind">

When using <abc [(bar)]="foo"/> syntax on angular.

This translates to: <abc [bar]="foo" (barChange)="foo = $event" />

Which means your component should have:

@Input() bar;
@Output() barChange = new EventEmitter();

To get checkbox work you should follow all these steps:

1. import FormsModule in your module

2. Put the input inside a form tag

3. your input should be like this:

   <input name="mpf" type="checkbox" [(ngModel)]="value" />
   

Note: do not forget to put name in your input.

I have done a custom component tried two way binding

Mycomponent: <input type="checkbox" [(ngModel)]="model" >

_model:  boolean;   
   
@Output() checked: EventEmitter<boolean> = new EventEmitter<boolean>();

@Input('checked')
set model(checked: boolean) {

  this._model = checked;
  this.checked.emit(this._model);
  console.log('@Input(setmodel'+checked);
}

get model() {
  return this._model;
}

strange thing is this works

<mycheckbox	 [checked]="isChecked" (checked)="isChecked = $event">
 

while this wont

<mycheckbox	 [(checked)]="isChecked">

You must add name="selected" attribute to input element.

For example:

<div class="checkbox">
  <label>
    <input name="selected" [(ngModel)]="saveUsername.selected" type="checkbox">Save username
  </label>
</div>

I know it may be repeated answer but for any one want to load list of checkboxes with selectall checkbox into angular form i follow this example: Select all/deselect all checkbox using angular 2+

it work fine but just need to add

[ngModelOptions]="{standalone: true}" 

the final HTML should be like this:

<ul>
    <li><input type="checkbox" [(ngModel)]="selectedAll" (change)="selectAll();"/></li>
    <li *ngFor="let n of names">
    <input type="checkbox" [(ngModel)]="n.selected" (change)="checkIfAllSelected();">{{n.name}}
    </li>
  </ul>

TypeScript

  selectAll() {
    for (var i = 0; i < this.names.length; i++) {
      this.names[i].selected = this.selectedAll;
    }
  }
  checkIfAllSelected() {
    this.selectedAll = this.names.every(function(item:any) {
        return item.selected == true;
      })
  }

hope this help thnx

In any situation, if you have to bind a value with a checkbox which is not boolean then you can try the below options

In the Html file:

<div class="checkbox">
<label for="favorite-animal">Without boolean Value</label>
<input type="checkbox" value="" [checked]="ischeckedWithOutBoolean == 'Y'" 
(change)="ischeckedWithOutBoolean = $event.target.checked ? 'Y': 'N'">
</div>

in the componentischeckedWithOutBoolean: any = 'Y';

See in the stackblitz https://stackblitz.com/edit/angular-5szclb?embed=1&file=src/app/app.component.html

Angular: "9.0.0"
Angular CLI: 9.0.1
Node: 13.10.1
OS: linux x64

.html file

<input [(ngModel)]="userConsent" id="userConsent" required type="checkbox"/> " I Accept"

.ts file

userConsent: boolean = false;

A workaround to achieve the same specially if you want to use checkbox with for loop is to store the state of the checkbox inside an array and change it based on the index of the *ngFor loop. This way you can change the state of the checkbox in your component.

app.component.html

<div *ngFor="let item of items; index as i"> <input type="checkbox" [checked]="category[i]" (change)="checkChange(i)"> {{item.name}} </div>

app.component.ts

items = [
    {'name':'salad'},
    {'name':'juice'},
    {'name':'dessert'},
    {'name':'combo'}
  ];

  category= []
  
  checkChange(i){
    if (this.category[i]){  
      this.category[i] = !this.category[i];
    }
    else{
      this.category[i] = true;
    }
  }

My angular directive like angularjs (ng-true-value ng-false-value)

@Directive({
    selector: 'input[type=checkbox][checkModel]'
})
export class checkboxDirective {
    @Input() checkModel:any;
    @Input() trueValue:any;
    @Input() falseValue:any;
    @Output() checkModelChange = new EventEmitter<any>();

    constructor(private el: ElementRef) { }

    ngOnInit() {
       this.el.nativeElement.checked = this.checkModel==this.trueValue;
    }

    @HostListener('change', ['$event']) onChange(event:any) {
        this.checkModel = event.target.checked ? this.trueValue : this.falseValue;
        this.checkModelChange.emit(this.checkModel);
    }

}

html

<input type="checkbox" [(checkModel)]="check" [trueValue]="1" [falseValue]="0">

In Angular p-checkbox,

Use all attributes of p-checkbox

<p-checkbox name="checkbox" value="isAC" 
    label="All Colors" [(ngModel)]="selectedAllColors" 
    [ngModelOptions]="{standalone: true}" id="al" 
    binary="true">
</p-checkbox>

And more importantly, don't forget to include [ngModelOptions]="{standalone: true} as well as it SAVED MY DAY.