错误:没有NgControl Angular AOT的提供者

Question

我正在尝试实现一个自定义ControlValueAccessor,因为Kara Erickson在最后一个Angular Connect https://youtu.be/CD_t3m2WMM8?t=20m22s上推荐.将有效状态从父组件传递给子组件.

app.component.html:

<app-country-select ngModel="model" name="country-select"></app-country-select>

国家select.component.html:

<select [formControl]="controlDir.control" #select placeholder="Country" i18n-placeholder (click)="onTouched()"
        (change)="onChange($event.value)" [required]="required">
  <option value="at">Austria</option>
  <option value="au">Australia</option>
</select>

国家select.component.ts:

@Component({
    selector: 'app-country-select',
    templateUrl: './country-select.component.html',
    styleUrls: ['./country-select.component.scss'],
})
export class CountrySelectComponent implements ControlValueAccessor {

    @Input() required = false;

    @ViewChild('select') select: HTMLSelectElement;

    onChange: (value: any) => void;
    onTouched: () => void;

    constructor(@Self() public controlDir: NgControl) {
      controlDir.valueAccessor = this;

    }
...
}

完整的代码存在于此:https://github.com/maksymzav/ngcontrol.

在JIT模式下运行代码时,代码运行正常.我想因为在运行时它确实知道它使用了哪个控件:NgModel,或FormControlName,或FormControlDirective.但是,当我运行AOT构建时,ng build --prod它失败并显示消息

错误输入:没有NgControl的提供者("[错误 - >] <app-country-select> </ app-country-select>")

有谁知道如何使这个构建成功？谢谢.

Answer 1

您可以添加@Optional()装饰器到您的controlDir.

将依赖项标记为可选的参数元数据.如果未找到依赖项,则Injector提供null.

在我的情况下,这解决了"无提供者"错误,我能够成功编译项目.

例:

constructor(
  @Optional() // Add this decorator
  @Self()
  public controlDir: NgControl,
  private stripe: StripeService,
  private cd: ChangeDetectorRef
) {
  // Better to add some checks here since controlDir can be null
  if (controlDir) {
    controlDir.valueAccessor = this;
  }
}