Angular2双向绑定选择选项不更新

Question

I have a select list that is bound to an Person property on my component using [ngValue]. When I change the select, the underyling selectedPerson property is updated as expected. However, the select does no default to the selected person on initialisation nor does it update if I change the selected person in code.

Any help into what I am missing would be greatly appreciated. Here's my code...

import {Component, OnInit, NgModule} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import { FormsModule } from '@angular/forms';

@Component({
  selector: 'my-app',
  template: `
      <form>
          <select [(ngModel)]="selectedPerson" 
                  name="selectedPerson">
              <option [ngValue]="null">Please choose...</option>
              <option *ngFor="let p of people"
                      [ngValue]="p"
                      [attr.selected]="p.personId === selectedPerson?.personId ? true : null ">{{p.name}}</option>
          </select>
          <p>The selected person is {{selectedPerson?.name}}</p>
          <button type="button" (click)="selectJane()">Select Jane</button>
          <button type="button" (click)="clearSelection()">Clear Selection</button>
      </form>`,
})
export class App implements OnInit {

  public ngOnInit() {

    this.people = [
      { personId: 1, name: "Tom" },
      { personId: 2, name: "Mary" },
      { personId: 3, name: "Jane" }
    ]
    this.selectedPerson = { personId: 2, name: "Mary" }
  }

  public people: Person[];
  public selectedPerson: Person;  

  public selectJane(){
    this.selectedPerson = { personId: 3, name: "Jane" }
  }

  public clearSelection(){
    this.selectedPerson = null;
  }  
}

export class Person {
  public personId: number;
  public name: string;
}

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

...and here's a Plunker http://plnkr.co/edit/ag94mZO9Zggg1kZx8jJV

Answer 1

The problem is, that by using ngValue , the select expects the same reference, not just a similar looking object.

You could add a method to select by name like this:

public selectByName(name: string) {
   this.selectedPerson = this.people.find(person => person.name === name);
}

And then call it in your ngOnInit() :

this.selectByName("Mary");
// or this.selectedPerson = this.people[2];

And in selectJane() :

public selectJane(){
    this.selectByName("Jane");
}

Your updated Plunker