Selects' events in Angular2

Question

Please, can you help me? It is supposed to be easy, but I can't find the solution. There is a form with two selects. When #select1 changes, #select2 needs to show data according to the value of #select1. For example, get cities of each state. Kind of :

//html

<select (change)="select2.getCities($event)" ng-control="userState">
    <option *ng-for="#state of states" [value]="state">{{state}}</option>
</select>

<select #select2 ng-control="userCity">
    <option *ng-for="#city of cities" [value]="city">{{city}}</option>
</select>

//the Component
@Component({ selector: 'user-management', appInjector: [FormBuilder] });
@View({ templateUrl: 'user-management.html', directives: [NgFor] });
export class userManagement {
    constructor(fb: FormBuilder){
        this.userForm = fb.group({
            userState: [],
            userCity: []
        });
        this.states = ['New York', 'Pennsylvania'];
        this.cities = {'New York': ['Albany', 'Buffalo'], 'Pennsylvania':['Pittsburgh', 'Philadelphia']};
    }
    getCities($event){
        return this.cities[$event.target.value];
    }
}

This, of course, doesn't work. PLEASE, do you know how it should be done? It's in alpha28.

Answer 1

This is how I would do it on Angular 2 RC5, with a model-driven approach and Observables. This could also be a search field where you then use debounceTime() to not hit your backend on every keystroke or manipulate the input further.

//The Component Type script
import { Component } from '@angular/core';
import { FormControl, FormGroup, FormBuilder } from '@angular/forms';

@Component({ 
  moduleId: module.id,
  selector: 'states-cities', 
  template: `
    <form [formGroup]="myForm" (ngSubmit)="onSubmit()">
       <select formControlName="state">
            <option *ngFor="let state of states" [value]="state" >{{state}}</option>
        </select>

        <select  formControlName="userCity">
            <option *ngFor="let city of cities" [value]="city">{{city}}</option>
        </select>
      </form>
     `
})
export class stateCitiesComponent {

   states:Array<string>;
   cities:Array<string>;
   citiesData:any;
   myForm:FormGroup;

   constructor(private formBuilder: FormBuilder) {
     this.states = ['New York', 'Pennsylvania'];
     this.cities = [];
     this.citiesData = {'New York': ['Albany', 'Buffalo'], 'Pennsylvania':['Pittsburgh', 'Philadelphia']};
     // Setup Form
     this.myForm = this.formBuilder.group({
       state: [''],
       userCity: ['']
     });

     // Now setup change detection with an Observable
     this.myForm.controls["state"].valueChanges
     .debounceTime(100) // wait a litle after the user input (ms)
     .subscribe(state => {
       this.cities = this.citiesData[state];
     });

   }


  onSubmit() {
    // do something
  }
}

You can read more about change detection here.

Answer 2

Answering with Angular 2 latest template syntax and Typescript component

   //The Component Type script
import {Component} from 'angular2/core';
import {NgForm}    from 'angular2/common'; 

@Component({ selector: 'states-cities', 
             template: `
                    <form (ngSubmit)="onSubmit()" #heroForm="ngForm"> 
                       <select  ngControl="state" #state="ngForm" (change)="getCities(state)">
                            <option *ngFor="#state of states" [value]="state" >{{state}}</option>
                        </select>

                        <select  ngControl="userCity" #select2="ngForm">
                            <option *ngFor="#city of cities" [value]="city">{{city}}</option>
                        </select>
                      </form>
                     `


           })
export class stateCitiesComponent {

     states= ['New York', 'Pennsylvania'];
     cities = [];
     citiesData={'New York': ['Albany', 'Buffalo'], 'Pennsylvania':['Pittsburgh', 'Philadelphia']};

    getCities(state){
         this.cities=this.citiesData[state.value];
    }
}