Angular 5 Debounce 自定义异步验证器

Question

我已经创建了一个自定义异步验证器，它使用一项服务来根据服务器验证电子邮件。然而，这意味着每次输入一个字符时服务器都会被命中，这是不好的。我在这里遵循了几个我无法开始工作的答案。

我的验证器:

import {FormControl, NG_ASYNC_VALIDATORS, Validator} from 
'@angular/forms';
import { Http } from '@angular/http';
import {Directive, forwardRef} from "@angular/core";
import {ValidateEmailService} from "../services/validate-email.service";
import {UserService} from "../services/user.service";

@Directive({
  selector: '[appEmailValidator]',
  providers: [
    { provide: NG_ASYNC_VALIDATORS, useExisting: forwardRef(() => EmailValidator), multi: true }
  ]
})
export class EmailValidator implements Validator {
  public validateEmailService: ValidateEmailService;

  constructor(
    private _http: Http,
    private _userService: UserService
  ) {
    this.validateEmailService = new ValidateEmailService(this._http, this._userService);
  }

  validate(c: FormControl) {
    return new Promise(resolve => {
      this.validateEmailService.validateEmail(c.value)
        .subscribe((res) => {
          console.log(res);
          if (res.valid) {
            resolve(null);
          } else {
            resolve({
              valid: {
                valid: false
              }
            });
          }
        });
      })
    }
}

它本身运行良好，但一旦我尝试向它添加某种形式的去抖动，我最终会破坏它。

我试过来自 this question 的答案我得到了类似 Type X is not assignable to type 'Observable<any>' 的错误等等

我通过使用 setTimeout 接近了但最终所做的只是停止该功能。

我的最终目标是仅在大约 600 毫秒内未更改输入时运行验证器，但满足于每 600-2000 毫秒仅验证一次。

为了更加清楚，validateEmail来自 ValidateEmailService 的方法:

public validateEmail(email: string) {

  let validateEmail = new ValidateEmail(email);

  return this._http.get(
    this.getUrl(validateEmail),
    this.getOptionArgs())
    .map((response: Response) => Object.assign(new UserEmailVerification(), response.json().UserEmailVerification));

}

Answer 1

我还没有看到异步验证器作为指令实现，而是作为分配给表单控件的验证器函数实现的。

这是我在类似情况下使用的示例验证器:

import { Injectable } from '@angular/core';
import { AbstractControl, AsyncValidatorFn } from '@angular/forms';
import { Observable, timer, of } from 'rxjs';
import { switchMap, map } from 'rxjs/operators';

import { MembershipsService } from '@app/memberships/memberships.service';

@Injectable()
export class MembershipsValidators {

  constructor (
    private membershipsService: MembershipsService,
  ) {}

  checkMembershipExists(email?: string): AsyncValidatorFn {
    return (control: AbstractControl): Observable<{ [key: string]: any } | null> => {
      if (control.value === null || control.value.length === 0) {
        return of(null);
      }
      else if (email && email === control.value) {
        return of(null);
      }
      else {
        return timer(500).pipe(
          switchMap(() => {
            return this.membershipsService.lookupMember(control.value).pipe(
              map(member => {
                if (!member) {
                  return { noMembership: { value: control.value } };
                }

                return null;
              })
            );
          })
        );
      }
    };
  }

}

它被导入并应用到表单控件中:

this.form = this.formBuilder.group({
  memberEmail: new FormControl('', {
    validators: [ Validators.required, Validators.pattern(regexPatterns.email) ],
    asyncValidators: [ this.membershipsValidators.checkMembershipExists() ],
  }),
});

这样，在同步验证器得到满足之前，异步验证器不会触发。