Angular 2 RC5 [(ngModel)] Databinding Failure

Question

I've been looking at this code for a bit now and I'm stuck: I have a form that I'm binding to a component model and the [(ngModel)] binding breaks the page - the page won't render. I get no compilation error and no runtime debugger error, but the page won't render.

On this page it appears the model is working fine - I can see the model value fine with {{todo.title}} but when I try to bind the value to a form control with [(ngModel)]="todo.title" the application breaks.

Here's the form:

<form name="form1" id="form1" novalidate>
    <div class="form-group">
        <div class="input-group">
            <span class="input-group-addon"><i class="fa fa-bookmark"></i> </span>
            <input class="form-control"
                    name="title"
                    [(ngModel)]="todo.title"
                    placeholder="Enter the title for this ToDo"
                    required >
        </div>
    </div>
</form>

and the super simple components:

import { Component } from '@angular/core';
import { ToDo } from './todo';
import { ToDoListComponent } from './todo-list';


@Component({
    selector: 'todo-entry',
    templateUrl: 'app/todo-entry.html'
})
export class ToDoEntryComponent {     

    todo:ToDo = new ToDo();   

    new() {
        this.todo = new ToDo();                
    }    
}

and:

import { Component } from '@angular/core';

@Component({})
export class ToDo {
    title:string = "new todo";
    entered:Date = new Date();
}

The code works (one way anyway) if I use:

value="{{todo.title}}"

I'm pretty sure the module loading and component references are all correct as everything else works as expected displaying model values, as long as I don't use [(ngModel)].

Any ideas what I'm missing here?

Answer 1

I think the problem is that angular sees your [(ngModel)] and thinks you're trying to use an angular form, but there are no other supporting directives. I have no idea why you're not getting a helpful error description though.

If I create a simple form that uses ngModel binding but does not otherwise use angular forms, I get this error:

Error: If ngModel is used within a form tag, either the name attribute must be set or the form control must be defined as 'standalone' in ngModelOptions.

 Example 1: <input [(ngModel)]="person.firstName" name="first">
 Example 2: <input [(ngModel)]="person.firstName" [ngModelOptions]="{standalone: true}">

So you can do what the error says and add [ngModelOptions]="{standalone: true}" to your control, or you can use the blanket ngNoForm on your form element:

<form name="form1" id="form1" novalidate noNoform>

Answer 2

Never fails - posted this and found the answer here after some additional searching: http://almerosteyn.com/2016/04/linkup-custom-control-to-ngcontrol-ngmodel

The problem was missing imports for the Forms module. In RC5 and later the following has to be added to the module definition:

 import { FormsModule } from '@angular/platform-browser';

and to the imports declaration in @NgModule:

@NgModule({
  imports: [ BrowserModule,FormsModule ],
  ...
}

It's a pain that this error triggered no error during compilation as most other missing modules seem to do. Not sure why this one is not complaining...

Additionally, I had to make sure that I used name=title in addition (or instead of) id=title. name attribute is required for bound form elements.