Angular2双向绑定以选择选项不更新 [英] Angular2 two-way binding to select option not updating

问题描述

我有一个选择列表，该列表使用[ngValue]绑定到组件上的Person属性.当我更改选择内容时，将按预期更新底层样式的selectedPerson属性.但是，如果在代码中更改所选人员，则select不会在初始化时默认为所选人员，也不会更新.

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.

对我所缺少的任何帮助将不胜感激.这是我的代码...

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 {}

...这是一个柱塞 http://plnkr.co/edit/ag94mZO9Zggg1kZx8jJV

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

推荐答案

问题是，通过使用ngValue，select期望使用相同的引用，而不仅仅是看起来相似的对象.

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

您可以添加一种通过名称进行选择的方法，如下所示:

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

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

然后在您的ngOnInit()中调用它:

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

在selectJane()中:

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

您更新的柱塞

这篇关于Angular2双向绑定以选择选项不更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！