Angular 4 - 验证器自定义函数这是未定义的

Question

我正在使用组件FormComponent构建一个应用程序.我正在使用角度核心的反应形式模块,并创建一个自定义验证器.该函数通过使用它来调用另一个函数 - 因为我认为它将引用FormComponent,但它引用的是'undefined'(？)

onInit中的代码定义FormGroup和FormControl,并在其外部定义函数

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;


  constructor(){}


  ngOnInit() {

    this.id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo
    ]);


    this.formInsurance = new FormGroup({
      id:this.id      
    })


  }


  foo(control:FormControl){
  this.boo();
  if(control.value){
    return {
      objToReturn: {
          returned: name
      }
    };
  }
  return null
}

boo(){
  console.log('boo')

}

}

Answer 1

从FormControl中调用时,foo方法中的上下文不引用FormComponent.

您可以使用bind自行设置上下文来执行以下操作来修复此行为:

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;


  constructor(){}


  ngOnInit() {

    const id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo.bind(this)
    ]);

    this.id = id;

    this.formInsurance = new FormGroup({
      id
    })
  }


  foo(control:FormControl) {
    this.boo();
    if(control.value){
        return {
          objToReturn: {
              returned: name
          }
        };
      }
    return null
  }

  boo(){
    console.log('boo')

  }
}

Answer 2

当然，另一种选择是箭头函数，它自动绑定到this上下文：

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators, ValidationErrors } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;

  constructor() {}

  ngOnInit() {
    this.id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo
    ]);

    this.formInsurance = new FormGroup({
      id:this.id      
    })
  }

  foo = (control: FormControl): ValidationErrors => {
    this.boo();
    if (control.value) {
      return {
        objToReturn: {
          returned: name
        }
      };
    }
    return null
  }

  boo() {
    console.log('boo')
  }
}