Angular Material (8) 重新加载页面时显示错误消息（来自验证程序）

Question

我是 Angular Material 的新手。我正在使用 Angular Material (8) 制作注册表。这样做时，我看到重新加载页面时显示错误消息（通过点击浏览器上的 "Refresh" 按钮）。该领域从未以任何方式、形状或形式被触及。

为什么会这样？

TIA

文件：register.component.html

[ ... snip ...]

       <div class="flex-register-form">

            <!-- Form -->
            <form [formGroup]="registerForm" (ngSubmit)="registerForm.valid && onSubmit()" class="text-center">

                <div class="form-col">
                    <div class="col">
                        <!-- First name -->
                        <div class="md-form">
                            <input required type="text" id="materialRegisterFormFirstName" class="form-control" mdbInput
                                formControlName="firstname" />
                            <label for="materialRegisterFormFirstName">First name</label>
                            <mat-error *ngIf="registerForm.controls['firstname'].hasError('required')" >First name is required</mat-error>
                        </div>

[ ... snip ...]

文件：register.component.ts

import { Component, OnInit } from '@angular/core';
import { RegisterModel } from '../../models/register.models';
import {  FormBuilder, FormGroup, Validators, FormControl } from '@angular/forms';


@Component({
  selector: 'app-register',
  templateUrl: './register.component.html',
  styleUrls: ['./register.component.scss']
})

export class RegisterComponent implements OnInit {

  user: RegisterModel = new RegisterModel();
  registerForm: FormGroup;

  constructor(private formBuilder: FormBuilder) {

  }

  ngOnInit() {
    this.registerForm = new FormGroup({
      'firstname': new FormControl(null, [Validators.required]),
      'lastname': new FormControl(null, [Validators.required, Validators.maxLength(25)]),
      'email': new FormControl(null, [Validators.required, Validators.email, Validators.maxLength(25)]),
      'password': new FormControl(null, [Validators.required, Validators.minLength(8), Validators.maxLength(25)]),
      'agree': new FormControl(null, [Validators.required])
    });
  }

  onSubmit() {
    console.log(" was submited ");
  }

}

Answer 1

这是因为根据验证，它处于待处理状态。但是，我们还没有触及控件，所以我们可以做的是，我们可以通过检查表单字段的控件状态 touched 来检查用户是否与控件交互。

更正

<mat-error *ngIf="registerForm.controls['firstname'].hasError('required') && registerForm.controls.firstname.touched" >First name is required</mat-error>

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