forms - 在 Angular 4 中，为什么异步验证的嵌套控件不会将其有效性传播到父 FormGroup？

Question

在我的 Angular 4.0.2 应用程序中，我有一个 FormGroup，其中包含一个实现了 ControlValueAccessor 和 Validator 的嵌套组件。该组件异步验证自身。问题是，即使嵌套组件有效，父 FormGroup 仍然无效。

但是，如果我只是将验证更改为同步验证，则有效性会正确传播到父组。

我已将其尽可能简化为以下 Plunker:

http://plnkr.co/edit/H26pqEE3sRkzKmmhrBgm

这是显示类似设置的第二个 Plunker，但这次输入 FormControl 直接位于 FormGroup 内，而不是嵌套组件的一部分。此处，异步验证正确传播:

http://plnkr.co/edit/DSt4ltoO1Cw2Nx1oXxbD

为什么我的异步验证器在组件内部定义时不传播其有效性？

---

这是第一个(损坏的)Plunker 的代码:

import {Component, NgModule, VERSION, forwardRef} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {FormsModule, ReactiveFormsModule} from '@angular/forms'
import {Observable} from 'rxjs/Rx'
import {
    FormGroup, FormControl, FormBuilder, Validators, AbstractControl, Validator,
    ControlValueAccessor, NG_VALUE_ACCESSOR, NG_VALIDATORS, ValidationErrors
} from '@angular/forms';


@Component({
  selector: 'my-app',
  template: `
<p>When validated asyncronously, why is the parent form group invalid even though its 
inner control is valid?</p>
<p>Try clearing the value to see the asyncronous validation at work.</p>
<p>Try swapping line 58 for 60 to change to syncronous validation, which propagates correctly.</p>
<hr />
<div><code>FormGroup valid = {{form.valid}}</code></div><br />
<div [formGroup]="form">
  <nested-control formControlName="nested"></nested-control>
</div>
<hr />
`
})
export class App {
  form: FormGroup;
  constructor(fb: FormBuilder) {
    this.form = fb.group({
      nested: ['required']
    });
  }
}


@Component({
    selector: 'nested-control',
    providers: [{
        provide: NG_VALUE_ACCESSOR, 
        useExisting: forwardRef(() => NestedControl),
        multi: true
    }, {
        provide: NG_VALIDATORS,
        useExisting: forwardRef(() => NestedControl),
        multi: true,
    }],
    template: `
<div [formGroup]="form">
  <input type="text" formControlName="input" (keyup)="keyup($event)">
  <code>NestedControl valid = {{form.controls.input.valid}}, errors = {{form.controls.input.errors|json}}</code>
</div>
`
})
export class NestedControl implements ControlValueAccessor, Validator {
  form: FormGroup;
  private propagateChange = () => {};

  constructor(fb: FormBuilder) {
    this.form = fb.group({
      // if we change the validation to be syncronous then everything works as expected:
      //input: [null, Validators.required]
      input: [null, null, this.asyncRequiredValidator]
    });
  }

  asyncRequiredValidator(control: AbstractControl): ValidationErrors {
    // run the built in required validator after 1 second
    return Observable.interval(1000).take(1).map(_ => {
      const result = Validators.required(control);
      console.log('result', result);
      return result;
    });
  }

  keyup() {
    this.propagateChange();
  }

  writeValue(v: any): void {
    this.form.setValue({ input: v });
  }

  registerOnChange(fn: any): void {
    this.propagateChange = fn;
  }

  registerOnTouched(fn: any): void {
  }

  validate(c: AbstractControl): ValidationErrors {
    return this.form.valid ? null : {invalid: true};
  }
}


@NgModule({
  imports: [ BrowserModule, FormsModule, ReactiveFormsModule ],
  declarations: [ App, NestedControl ],
  bootstrap: [ App ]
})
export class AppModule {}

Answer 1

有几个问题我终于弄明白了，但我不确定这个解决方案是否是最优的。

首先，该组件需要提供 NG_ASYNC_VALIDATORS 而不是 NG_VALIDATORS(尽管像往常一样我无法在任何地方找到它的明确记录):

@Component({
    selector: 'nested-control',
    providers: [{
        provide: NG_ASYNC_VALIDATORS,  // <----- this
        useExisting: forwardRef(() => NestedComponent),
        multi: true,
    } ... 

接下来，它应该实现 AsyncValidator 而不是 Validator:

export class NestedComponent implements ControlValueAccessor, AsyncValidator {
    ...
    validate(c: AbstractControl): Observable<ValidationErrors | null> {
        // must return result wrapped in Observable
        return Observable.of(this.form.valid ? null : {invalid: true});
    }   
}

最后，在验证之后，我们必须显式传播更改。我必须使用 setTimeout 来确保传播运行验证程序后 的状态，而不是当前状态。这对我来说似乎很老套，所以如果有人知道更好的方法，请告诉我。

asyncRequiredValidator(control: AbstractControl): ValidationErrors {
    // run the built in required validator after 1 second
    return Observable.interval(1000).take(1).map(_ => {
      const result = Validators.required(control);
      console.log('result', result);
      setTimeout(() => this.propagateChange());   // <!---- propagate post-validation state
      return result;
    });
  }

这是修复了所有这些问题的 Plunker:

http://plnkr.co/edit/6uSWVhdFgyHTvYjHlgmN?p=preview