Angular - 无法绑定到“ngValue”，因为它不是“mat-option”的已知属性

Question

I'm using angular 5 and I'm getting the console error:

Can't bind to 'ngValue' since it isn't a known property of 'mat-option'

My template looks something like as follows:

  <mat-select placeholder="Select Book" name="patient" [(ngModel)]="selectedBook">
     <mat-option *ngFor="let eachBook of books" [ngValue]="eachBook">{{eachBook.name}}</mat-option>
  </mat-select>

I've imported both MatSelectModule and MatOptionModule .

How can we resolve this?

Answer 1

The accepted answer is not a solution but a work-around, as value and [ngValue] serve different purposes. value can be used for simple string values, whereas [ngValue] is necessary to support non-string values.

Per the documentation:

If you have imported the FormsModule or the ReactiveFormsModule, this value accessor will be active on any select control that has a form directive. You do not need to add a special selector to activate it.

If you are getting this error, you most likely need to import either FormsModule or ReactiveFormsModule into your app.

For example, in app.module.ts :

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

// ...

imports: [
    FormsModule,
    ...
]

Answer 2

你应该使用价值

[value]="eachBook"

Answer 3

I have met the same issue. The solution for me is to import 'ReactiveFormsModule'. So you can use [ngValue] to bind an object.

Answer 4

for mat-autocomplete, to use items instead of strings, for mat-option, ngValue wasn't available, however with [value], we can access the object by using option.value instead of option.viewValue:

allFruits: Item[] = [
    {
      name: 'hello',
      selected: true,
    },
    {
      name: 'world',
      selected: false,
    }
  ];


<mat-autocomplete #auto="matAutocomplete" (optionSelected)="selected($event)">
    <mat-option *ngFor="let fruit of filteredFruits | async" [value]="fruit">
      {{fruit.name}} {{fruit.selected}}
    </mat-option>
  </mat-autocomplete>


selected(event: MatAutocompleteSelectedEvent): void {
    console.log('selected ', event.option.value); <----- THIS
    console.log('selected ', event.option.viewValue); <---- NOT THIS
}

with option.value you get the object. With option.viewValue you will get a string representation of the innerHTML that the user sees.