Can't bind to 'formControl' since it isn't a known property of 'input' - angular2 material Autocomplete issue

问题

I am trying to use angular material autocomplete component in my angular2 project. I added following to my template.

<md-input-container>
    <input mdInput placeholder="Category" [mdAutocomplete]="auto" [formControl]="stateCtrl">
</md-input-container>

<md-autocomplete #auto="mdAutocomplete">
    <md-option *ngFor="let state of filteredStates | async" [value]="state">
        {{ state }}
    </md-option>
</md-autocomplete>

Following is my component.

import {Component, OnInit} from "@angular/core";
import {ActivatedRoute, Router} from "@angular/router";
import {FormControl} from "@angular/forms";

@Component({
    templateUrl: './edit_item.component.html',
    styleUrls: ['./edit_item.component.scss']
})
export class EditItemComponent implements OnInit {
    stateCtrl: FormControl;
    states = [....some data....];

    constructor(private route: ActivatedRoute, private router: Router) {
        this.stateCtrl = new FormControl();
        this.filteredStates = this.stateCtrl.valueChanges.startWith(null).map(name => this.filterStates(name));
    }
    ngOnInit(): void {
    }
    filterStates(val: string) {
        return val ? this.states.filter((s) => new RegExp(val, 'gi').test(s)) : this.states;
    }
}

I'm getting the following error. It looks like the formControl directive is not being found.

Can't bind to 'formControl' since it isn't a known property of 'input'

What is the issue here?

回答1:

While using formControl, you have to import ReactiveFormsModule to your imports array.

Example:

import {FormsModule, ReactiveFormsModule} from '@angular/forms';

@NgModule({
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    MaterialModule,
  ],
  ...
})
export class AppModule {}

回答2:

Forget trying to decipher the example .ts - as others have said it is often incomplete.

Instead just click on the 'pop-out' icon circled here and you'll get a fully working StackBlitz example.

You can quickly confirm the required modules:

Comment out any instances of ReactiveFormsModule, and sure enough you'll get the error:

Template parse errors:
Can't bind to 'formControl' since it isn't a known property of 'input'. 

回答3:

Start by adding a regular matInput to your template. Let's assume you're using the formControl directive from ReactiveFormsModule to track the value of the input.

Reactive forms provide a model-driven approach to handling form inputs whose values change over time. This guide shows you how to create and update a simple form control, progress to using multiple controls in a group, validate form values, and implement more advanced forms.

import { FormsModule, ReactiveFormsModule } from "@angular/forms"; //this to use ngModule

...

imports: [
    BrowserModule,
    AppRoutingModule,
    HttpModule,
    FormsModule,
    RouterModule,
    ReactiveFormsModule,
    BrowserAnimationsModule,
    MaterialModule],

来源：https://stackoverflow.com/questions/43220348/cant-bind-to-formcontrol-since-it-isnt-a-known-property-of-input-angular