typescript - Angular 2 custom form input

Question

How can I create custom component which would work just like native <input> tag? I want to make my custom form control be able to support ngControl, ngForm, [(ngModel)].

As I understand, I need to implement some interfaces to make my own form control work just like native one.

Also, seems like ngForm directive binds only for <input> tag, is this right? How can i deal with that?

---

Let me explain why I need this at all. I want to wrap several input elements to make them able to work together as one single input. Is there other way to deal with that? One more time: I want to make this control just like native one. Validation, ngForm, ngModel two way binding and other.

ps: I use Typescript.

Answer 1

I don't understand why every example I find on the internet has to be so complicated. When explaining a new concept, I think it's always best to have the most simple, working example possible. I've distilled it down a little bit:

HTML for external form using component implementing ngModel:

EmailExternal=<input [(ngModel)]="email">
<inputfield [(ngModel)]="email"></inputfield>

Self-contained component (no separate 'accessor' class - maybe I'm missing the point):

import {Component, Provider, forwardRef, Input} from "@angular/core";
import {ControlValueAccessor, NG_VALUE_ACCESSOR, CORE_DIRECTIVES} from "@angular/common";

const CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR = new Provider(
  NG_VALUE_ACCESSOR, {
    useExisting: forwardRef(() => InputField),
    multi: true
  });

@Component({
  selector : 'inputfield',
  template: `<input [(ngModel)]="value">`,
  directives: [CORE_DIRECTIVES],
  providers: [CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR]
})
export class InputField implements ControlValueAccessor {
  private _value: any = '';
  get value(): any { return this._value; };

  set value(v: any) {
    if (v !== this._value) {
      this._value = v;
      this.onChange(v);
    }
  }

    writeValue(value: any) {
      this._value = value;
      this.onChange(value);
    }

    onChange = (_) => {};
    onTouched = () => {};
    registerOnChange(fn: (_: any) => void): void { this.onChange = fn; }
    registerOnTouched(fn: () => void): void { this.onTouched = fn; }
}

In fact, I've just abstracted all of this stuff to an abstract class which I now extend with every component I need to use ngModel. For me this is a ton of overhead and boilerplate code which I can do without.

Edit: Here it is:

import { forwardRef } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';

export abstract class AbstractValueAccessor implements ControlValueAccessor {
    _value: any = '';
    get value(): any { return this._value; };
    set value(v: any) {
      if (v !== this._value) {
        this._value = v;
        this.onChange(v);
      }
    }

    writeValue(value: any) {
      this._value = value;
      // warning: comment below if only want to emit on user intervention
      this.onChange(value);
    }

    onChange = (_) => {};
    onTouched = () => {};
    registerOnChange(fn: (_: any) => void): void { this.onChange = fn; }
    registerOnTouched(fn: () => void): void { this.onTouched = fn; }
}

export function MakeProvider(type : any){
  return {
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => type),
    multi: true
  };
}

Here's a component that uses it: (TS):

import {Component, Input} from "@angular/core";
import {CORE_DIRECTIVES} from "@angular/common";
import {AbstractValueAccessor, MakeProvider} from "../abstractValueAcessor";

@Component({
  selector : 'inputfield',
  template: require('./genericinput.component.ng2.html'),
  directives: [CORE_DIRECTIVES],
  providers: [MakeProvider(InputField)]
})
export class InputField extends AbstractValueAccessor {
  @Input('displaytext') displaytext: string;
  @Input('placeholder') placeholder: string;
}

HTML:

<div class="form-group">
  <label class="control-label" >{{displaytext}}</label>
  <input [(ngModel)]="value" type="text" placeholder="{{placeholder}}" class="form-control input-md">
</div>