错误：没有NgControl Angular AOT的提供者 [英] ERROR in : No provider for NgControl Angular AOT

问题描述

我正在尝试实现一个自定义ControlValueAccessor，就像Kara Erickson在上一个Angular Connect https：// youtu。是/ CD_t3m2WMM8？t = 20m22s 。将有效状态从父组件传递给子组件。

I am trying to implement a custom ControlValueAccessor as Kara Erickson recommended on last Angular Connect https://youtu.be/CD_t3m2WMM8?t=20m22s . To pass the validity state from the parent component to the child one.

app.component.html：

app.component.html:

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

country-select.component.html：

country-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>

country-select.component.ts：

country-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;

    }
...
}

完整代码存在于此处： https://github.com/maksymzav/ngcontrol 。

The full code lives here: 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。
但是当我使用 ng build --prod 运行AOT构建时，它失败并显示消息

The code works perfectly when running it in the JIT mode. I guess because in runtime it does know with which control it is used: NgModel, or FormControlName, or FormControlDirective. But when I run an AOT build with ng build --prod it fails with message

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

ERROR in : No provider for NgControl ("[ERROR ->]<app-country-select></app-country-select>")

有谁知道如何使这个构建成功？谢谢。

Does anyone know how to make this build successful? Thank you.

推荐答案

你可以添加 @Optional（） decorator到你的 controlDir 。

将依赖关系标记为可选的参数元数据。如果找不到依赖项，则注入器
提供null。

A parameter metadata that marks a dependency as optional. Injector provides null if the dependency is not found.

在我的情况下，这解决了No provider错误，我能够成功编译该项目。

In my case, that solved the "No provider" error and I was able to successfully compile the project.

示例：

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;
  }
}

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