javascript - Angular 9 - 无法绑定(bind)到 'formGroup'，因为它不是 'form' 的已知属性

Question

这个问题已经有答案了:

Can't bind to 'formGroup' since it isn't a known property of 'form' (48 个回答)

已关闭 去年。

我的代码环境是Angular 9，当我设置响应式(Reactive)表单时，遇到了这个错误:

error NG8002: Can't bind to 'formGroup' since it isn't a known property of 'form'.

我在 Google 和 StackOverflow 中做了一些研究，但找不到使用 Angular 9 的相同问题，但是，根据其他帖子的建议，我确实将 ReactiveFormsModule 导入到 app.module.ts、routing.module.ts 和还有recipe-edit.component.spec.ts 文件。但是，错误不断弹出。我附上我的代码，有人可以给我建议吗？

app.module.ts

import { RecipeService } from './recipes/recipe.service';
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule, ReactiveFormsModule} from '@angular/forms';

import { RoutingModule } from './routing.module';
import { ShoppingListService } from './shopping-list/shopping-list.service';
import { AppComponent } from './app.component';
import { RecipesComponent } from './recipes/recipes.component';
import { RecipeListComponent } from './recipes/recipe-list/recipe-list.component';
import { RecipeItemComponent } from './recipes/recipe-list/recipe-item/recipe-item.component';
import { RecipeDetailComponent } from './recipes/recipe-detail/recipe-detail.component';
import { HeaderComponent } from './header/header.component';
import { ShoppingListComponent } from './shopping-list/shopping-list.component';
import { ShoppingEditComponent } from './shopping-list/shopping-edit/shopping-edit.component';
import { DropdownDirective } from './shared/dropdown.directive';

@NgModule({
  declarations: [
    AppComponent,
    RecipesComponent,
    RecipeListComponent,
    RecipeItemComponent,
    RecipeDetailComponent,
    HeaderComponent,
    ShoppingListComponent,
    ShoppingEditComponent,
    DropdownDirective
  ],
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    RoutingModule
  ],
  providers: [ShoppingListService, RecipeService],
  bootstrap: [AppComponent]
})
export class AppModule { }

路由.module.ts

import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { RecipeStartComponent } from './recipes/recipe-start/recipe-start.component';
import { RecipeDetailComponent } from './recipes/recipe-detail/recipe-detail.component';
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

import { ShoppingListComponent } from './shopping-list/shopping-list.component';
import { RecipesComponent } from './recipes/recipes.component';
import { RecipeEditComponent } from './recipes/recipe-edit/recipe-edit.component';

const routes: Routes = [
  {path: '', redirectTo: '/recipes', pathMatch: 'full'},
  {path: 'recipes', component: RecipesComponent, children: [
    {path: '', component: RecipeStartComponent},
    {path: 'new', component: RecipeEditComponent},
    {path: ':id', component: RecipeDetailComponent},
    {path: ':id/edit', component: RecipeEditComponent}
  ]},
  {path: 'shopping-list', component: ShoppingListComponent}
  ];
@NgModule({
  imports: [RouterModule.forRoot(routes), FormsModule, ReactiveFormsModule],
  exports: [RouterModule]
})
export class RoutingModule {}

食谱编辑.component.ts

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';
import { FormGroup, FormControl } from '@angular/forms';

import { RecipeService } from './../recipe.service';

@Component({
  selector: 'app-recipe-edit',
  templateUrl: './recipe-edit.component.html',
  styleUrls: ['./recipe-edit.component.css']
})
export class RecipeEditComponent implements OnInit {
  id: number;
  editMode = false;
  recipeForm: FormGroup;

  constructor(private route: ActivatedRoute, private recipeService: RecipeService) { }

  ngOnInit() {
    this.route.params
      .subscribe(
        (paras: Params) => {
          this.id = +paras.id;
          this.editMode = paras.id != null;
          this.initForm();
        }
      );
  }

  private initForm() {
    let name = '';
    let imagePath = '';
    let description = '';

    if (this.editMode) {
      const editRecipe = this.recipeService.getRecipe(this.id);
      name = editRecipe.name;
      imagePath = editRecipe.imagePath;
      description = editRecipe.desc;
    }

    this.recipeForm = new FormGroup({
      name: new FormControl(name),
      imagePath: new FormControl(imagePath),
      description: new FormControl(description)
    });
  }

  onSubmit() {
    console.log(this.recipeForm);
  }
}

recipe-edit.component.html

<div class="row">
  <div class="col-xs-12">
    <form (ngSubmit) = "onSubmit()" [formGroup] = "recipeForm" >
      <div class="row">
        <div class="col-xs-12">
          <button class="btn btn-success" type = "submit"> Save </button>
          <button class="btn btn-danger" type = "button"> Cancel </button>
        </div>
      </div>
      <div class="row">
        <div class="col-xs-12">
          <div class="form-group">
            <label for="name"> Recipe Name</label>
            <input
              type = "text"
              id = "name"
              formControlName="name"
              class="form-control">
          </div>
        </div>
      </div>
      <div class="row">
        <div class="col-xs-12">
          <div class="form-group">
            <label for="imagePath"> Image URL </label>
            <input
              type = "text"
              id = "imagePath"
              formControlName="imagePath"
              class="form-control">
          </div>
        </div>
      </div>
      <div class="row">
        <div class="col-xs-12">
          <img src="" class="img-reponsive">
        </div>
      </div>
      <div class="row">
        <div class="col-xs-12">
          <div class="form-group">
            <label for="description"> Description </label>
            <textarea
              type = "text"
              id = "description"
              formControlName="description"
              class="form-control"
              rows = "6"></textarea>
          </div>
        </div>
      </div>
      <div class="row">
        <div class="col-xs-12">
          <div class="row">
            <div class="col-xs-8">
              <input
                type = "text"
                class = "form-control">
              </div>
              <div class="col-xs-2">
                <input
                type = "number"
                class = "form-control">
            </div>
            <div class="col-xs-2">
              <button class="btn btn-danger" type = "button"> X </button>
            </div>
          </div>
        </div>
      </div>
    </form>
  </div>
</div>

配方编辑.component.spec.ts

import { async, ComponentFixture, TestBed } from '@angular/core/testing';

import { RecipeEditComponent } from './recipe-edit.component';
import { ReactiveFormsModule, FormsModule } from '@angular/forms';

describe('RecipeEditComponent', () => {
  let component: RecipeEditComponent;
  let fixture: ComponentFixture<RecipeEditComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ RecipeEditComponent ],
      imports: [ReactiveFormsModule, FormsModule]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(RecipeEditComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

Answer 1

如果RecipeEditComponent属于AppModule，则需要在app.module.ts中声明RecipeEditComponent:

import { RecipeService } from './recipes/recipe.service';
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule, ReactiveFormsModule} from '@angular/forms';

import { RoutingModule } from './routing.module';
import { ShoppingListService } from './shopping-list/shopping-list.service';
import { AppComponent } from './app.component';
// Add following line:
import { RecipeEditComponent } from './recipes/recipe-edit/recipe-edit.component'; // add this
import { RecipesComponent } from './recipes/recipes.component';
import { RecipeListComponent } from './recipes/recipe-list/recipe-list.component';
import { RecipeItemComponent } from './recipes/recipe-list/recipe-item/recipe-item.component';
import { RecipeDetailComponent } from './recipes/recipe-detail/recipe-detail.component';
import { HeaderComponent } from './header/header.component';
import { ShoppingListComponent } from './shopping-list/shopping-list.component';
import { ShoppingEditComponent } from './shopping-list/shopping-edit/shopping-edit.component';
import { DropdownDirective } from './shared/dropdown.directive';

@NgModule({
  declarations: [
    AppComponent,
    RecipesComponent,
    RecipeEditComponent, // add this and the import line
    RecipeListComponent,
    RecipeItemComponent,
    RecipeDetailComponent,
    HeaderComponent,
    ShoppingListComponent,
    ShoppingEditComponent,
    DropdownDirective
  ],
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    RoutingModule
  ],
  providers: [ShoppingListService, RecipeService],
  bootstrap: [AppComponent]
})
export class AppModule { }

否则如果它属于另一个模块，则需要在其所属模块中导入 FormsModule 和 ReactiveFormsModule