Angular 2 - 2 Way Binding with NgModel in NgFor

Question

In Angular 2 how would I get 2 way binding with NgModel within a repeating list using NgFor. Below is my plunkr and code but I get an error.

Plunkr

@Component({
  selector: 'my-app',
  template: `
  <div>
    <div *ngFor="let item of toDos;let index = index;">
      <input [(ngModel)]="item" placeholder="item">
    </div>
    Below Should be binded to above input box
    <div *ngFor="let item of toDos">
      <label>{{item}}</label>
    </div>
  </div>
  `,
  directives: [MdButton, MdInput]
})
export class AppComponent { 
  toDos: string[] =["Todo1","Todo2","Todo3"];
  constructor() {}
  ngOnInit() {
  }
}

Answer 1

After digging around I need to use trackBy on ngFor. Updated plnkr and code below. Hope this helps others.

Working Plnkr

@Component({
  selector: 'my-app',
  template: `
  <div>
    <div *ngFor="let item of toDos;let index = index;trackBy:trackByIndex;">
      <input [(ngModel)]="toDos[index]" placeholder="item">
    </div>
    Below Should be binded to above input box
    <div *ngFor="let item of toDos">
      <label>{{item}}</label>
    </div>
  </div>
  `,
  directives: [MdButton, MdInput]
})
export class AppComponent { 
  toDos: string[] =["Todo1","Todo2","Todo3"];
  constructor() {}
  ngOnInit() {
  }
  trackByIndex(index: number, obj: any): any {
    return index;
  }
}

Answer 2

What you have done is not working because of two reasons.

• You have to use toDos[index] instead of item with ngModel (Read for more info )
• Each input has to have a unique name

Here's the working solution for your problem.

<div>
<div *ngFor="let item of toDos;let index = index;">
  <input name=a{{index}} [(ngModel)]="toDos[index]" placeholder="item">
</div>
Below Should be binded to above input box
<div *ngFor="let item of toDos">
  <label>{{item}}</label>
</div>

Answer 3

Try this

@Component({
  selector: 'my-app',
  template: `
  <div>
    <div *ngFor="let item of toDos;let index = index;">
  <input [(ngModel)]="item.text" placeholder="item.text">
    </div>
    Below Should be binded to above input box
    <div *ngFor="let item of toDos">
  <label>{{item.text}}</label>
    </div>
  </div>
  `,
  directives: [MdButton, MdInput]
   })
export class AppComponent { 
  toDos: any[] =[{text:"Todo1"},{text:"Todo2"},{text:"Todo3"}];
  constructor() {}
  ngOnInit() {
  }
}

Answer 4

You have to add a name attribute to the ngModel with name + index to make it unique.

<mat-form-field
  #fileNameRef
  appearance="fill"
  color="primary"
  floatLabel="auto"
>
  <input
    matInput
    #fileNameCtrl="ngModel"
    name="originalName{{ index }}"
    [(ngModel)]="file.originalName"
    type="text"
    autocomplete="off"
    autocapitalize="off"
    readonly
  /> 
</mat-form-field>