Angular 7 种反应形式 "No value accessor for form control with unspecified name attribute"

Question

我正在使用反应式表单，我似乎对看似随机的表单字段有疑问。关于为什么会发生这种情况的任何想法都是有争议的。

我刚开始使用 angular 和 material 7 如果有帮助的话

有趣的是，在表单中添加和删除元素会导致其他元素出现问题。

ERROR Error: No value accessor for form control with unspecified name attribute

TS

export class VolunteerApplicationPersonalStepComponent implements OnInit 
{

  public readonly form: FormGroup;
    constructor(private fb: FormBuilder) {
        this.form = this.fb.group({
          businessTelephoneExt: [''],
          otherTelephone: [''],
          otherTelephoneExt: [''],
        });
      }
}

HTML

    <form [formGroup]="form">

     <mat-form-field>
        <input matInput i18n-placeholder placeholder="Business Extension"
               [formControl]="form.get('businessTelephoneExt')">
      </mat-form-field>

      <app-telephone-input i18n-placeholder placeholder="Other Telephone"
                           [formControl]="form.get('otherTelephone')">
      </app-telephone-input>

      <mat-form-field>
        <input matInput i18n-placeholder placeholder="Other Extension"
               [formControl]="form.get('otherTelephoneExt')">
      </mat-form-field>

      <br>

      <div class="group-margin group-min-width">
        <button mat-stroked-button color="primary" matStepperPrevious i18n>Previous</button>
        <button mat-raised-button color="primary" matStepperNext (click)="next()" i18n>Next</button>
      </div>
    </form>

正如有人建议的那样.. formControlName="businessTelephoneExt"

App-Telephone 代码（注意它曾经有 formControl 而不是 appFormControl）

export class TelephoneInputComponent implements OnInit {

  @Input() public required = false;
  @Input() public placeholder = '';
  @Input() public appFormControl: NgControl;

  constructor() {
  }

  public ngOnInit() {
  }
}



<mat-form-field>
  <input
    matInput
    type="tel"
    [required]="required"
    [placeholder]="placeholder"
    [formControl]="appFormControl">

  <mat-hint i18n>Please enter digits only</mat-hint>

  <mat-error
    *ngIf="appFormControl.hasError('phone')"
    i18n>Invalid phone (requires 10 digits)
  </mat-error>
</mat-form-field>

Answer 1

似乎你不能有一个名为 formControl 的 @Input()

Answer 2

从父组件中删除 otherTelephone 表单控件并从子组件中添加 otherTelephone

export class VolunteerApplicationPersonalStepComponent implements OnInit 
{

  public readonly form: FormGroup;
    constructor(private fb: FormBuilder) {
        this.form = this.fb.group({
          businessTelephoneExt: [''],
          otherTelephoneExt: [''],
        });
      }
}

使用controlContainer为子组件提供父表单实例，然后注入FormGroupDiretive获取父表单实例

apptelephoneinput.component.html

@Component({
  selector: 'app-telephone-input',
  templateUrl: './app-telephone-input.component.html',
  styleUrls: ['./app-telephone-input.component.css'],
  viewProviders: [{ provide: ControlContainer, useExisting: FormGroupDirective 
}]
})
export class TelephoneInputComponent implements OnInit {   
  @Input() public required = false;
  @Input() public placeholder = '';
  childForm;
  constructor(private parentF: FormGroupDirective) { }

  ngOnInit() {
    this.childForm = this.parentF.form;
    this.childForm.addControl('otherTelephone', new FormControl(''))
  }

}

app-电话-input.component.html

<mat-form-field>
  <input
    matInput
    type="tel"
    [required]="required"
    [placeholder]="placeholder"
    formControl="otherTelephone">

示例：https://stackblitz.com/edit/angular-fktkdk

Answer 3

我看到的一件小事是：

  <app-telephone-input i18n-placeholder placeholder="Other Telephone"
                       [formControl]="form.get('otherTelephone')">
  </app-telephone-input>

所以应该是：

  <app-telephone-input i18n-placeholder placeholder="Other Telephone"
                       [appFormControl]="form.get('otherTelephone')">
  </app-telephone-input>

如果您想创建自定义表单控制器，您应该实现 ControlValueAccessor 接口

ControlValueAccessor {
  writeValue(obj: any): void
  registerOnChange(fn: any): void
  registerOnTouched(fn: any): void
  ...
}

如果您只实现 ControlValueAccessor 接口，您可以绑定属性 formControl

Answer 4

@ricardo 的不正确

在使用 ControlValueAccessor 接口时，您可以有一个名为 formControl 的 @Input()，很可能您还没有向提供者添加 NG_VALUE_ACCESSOR 令牌。类似于：

export const VALUE_ACCESSOR: any = {
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => MyComponent),
    multi: true,
};

@Component({
    selector: 'my-component',
    templateUrl: './my-component.component.html',
    styleUrls: ['./my-component.component.scss'],
    providers: [VALUE_ACCESSOR]
})

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angular7