如果我在不输入任何内容的情况下通过文本输入进行制表,则显示错误msg divs,指示所需的验证程序已正确触发。但是,如果我在任何一个字段中键入任何内容,则控制台会立即引发此错误:

Cannot read property 'required' of null

这是我的组件:
import { PasswordValidators } from './../validators/password.validators';
import { Component, OnInit } from '@angular/core';
import { FormBuilder, Validators, FormGroup, FormControl } from '@angular/forms';

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

  form;

  constructor(fb: FormBuilder) {
    this.form = fb.group({
      newPassword: ['', Validators.required],
      confirmPassword: ['', Validators.required]
    })
  }

  get newPassword() {
    return this.form.get('newPassword');
  }

  get confirmPassword() {
    return this.form.get('confirmPassword');
  }

}

和HTML:
<form [formGroup]="form">
  <div class="form-group">
    <label for="newPassword">New Password</label>
    <input formControlName="newPassword" id="newPassword" type="text" class="form-control">
    <div class="alert alert-danger" *ngIf="newPassword.touched && newPassword.errors.required">
      Required
    </div>
  </div>
  <div class="form-group">
    <label for="confirmPassword">Confirm Password</label>
    <input formControlName="confirmPassword" id="confirmPassword" type="text" class="form-control">
    <div class="alert alert-danger" *ngIf="confirmPassword.touched && confirmPassword.errors.required">
      Required
    </div>
  </div>

  <p><button class="btn btn-primary">Submit</button></p>

</form>

最佳答案

该错误是由以下原因引起的:

*ngIf="newPassword.touched && newPassword.errors.required"

当您输入一个值时,不再有错误集合,因此检查newPassword.errors.required会生成该Cannot read property 'required' of null错误。

尝试这样的事情:
*ngIf="newPassword.touched && newPassword.errors?.required"

例如,我的看起来像这样:
            <div class="col-md-8">
                <input class="form-control"
                        id="productNameId"
                        type="text"
                        placeholder="Name (required)"
                        required
                        minlength="3"
                        [(ngModel)] = product.productName
                        name="productName"
                        #productNameVar="ngModel" />
                <span class="help-block" *ngIf="(productNameVar.touched ||
                                                 productNameVar.dirty || product.id !== 0) &&
                                                 productNameVar.errors">
                    <span *ngIf="productNameVar.errors.required">
                        Product name is required.
                    </span>
                    <span *ngIf="productNameVar.errors.minlength">
                        Product name must be at least three characters.
                    </span>
                </span>
            </div>

10-05 20:51
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