javascript - 我收到以下错误 : ERROR TypeError: Cannot read property 'invalid' of undefined

Question

我尝试过其他解决方案，例如修复表单引用，但这对我没有帮助。这是我的登录表单

    <form [formGroup]="longinForm" (ngSubmit)="onSubmit()">
    <h1>Login Form</h1>

      <div class="form-group" >
        <label for="name" >Username</label>
        <input type="text" name ="user" [(ngModel)]="loginuserdata.user" 
 #user="ngModel" 
        class="form-control" required >
        <div *ngIf="submitted">
        <div [hidden]="user.valid || user.pristine" class="alert alert-danger">
          Username is required
        </div>
        </div>
      </div>

      <div class="form-group" >
        <label for="pass" >Password</label>
        <input type="text" name="pass" [(ngModel)]="loginuserdata.pass" #pass="ngModel"
        class="form-control"  required >
        <div *ngIf="submitted">
        <div [hidden]="pass.valid || pass.pristine" class="alert alert-danger">
            Password is required
        </div>
        </div>
      </div>
      <button type="submit" class="btn btn-success">Submit</button>
    </form>

这也是我的登录组件

import { Component, OnInit, ViewChild } from '@angular/core';
import { NgForm, FormGroup } from '@angular/forms';
import { Router } from '@angular/router';
import { LoginService } from './login.service';
import { ILoginData } from './login-data';

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

  loginForm:FormGroup;
  loginuserdata : any[] = [];
  error:string;

  submitted=false;

  constructor(private route: Router,private service:LoginService) { }

  get f(){return this.loginForm.controls;}

  ngOnInit() {
    this.onSubmit();
  }

  onSubmit(){

    if(this.loginForm.invalid){return;}//form invalid stop here
    //form is valid do something
    this.submitted=true;
    if(this.f.user.value == "Admin" && this.f.pass.value == "Apassword"){
    this.service.getAdmin()
    .subscribe(data => this.loginuserdata = data)
              this.route.navigateByUrl('admin');
              err => this.error = err;
              console.log(this.error);
    }

  }

}

如果你们需要查看我的代码的任何其他部分，请告诉我，请帮助我，我尝试了类似于解决此问题的答案，但它对我不起作用。

Answer 1

您需要构建表单控件，您已经定义了它，但您需要如下所示的内容。您需要初始化表单组。

import { NgForm, FormGroup, FormBuilder } from '@angular/forms'; 

//Be sure to import formBuilder and inject through constructor. This will allow you 
//to manage how you will build the form and add validation.
//Its a helper class provided by Angular to help us explicitly declare forms.

constructor( private formBuilder: FormBuilder ){}

public ngOnInit(): void {
    this.loginForm = this.formBuilder.group({
    username: ['', Validators.required],
    password: ['', Validators.required]
});

您可以在此处定义表单组的控件和验证器。 (这个例子只是表明每个值都需要有一个值才能有效。这应该构建在 ngOnInit 中。

然后在您的模板中，您可以删除 [(ngModel)] 并使其如下所示。当您需要访问输入的值时，该值将保存在控件中。

<form [formGroup]="loginForm" (ngSubmit)="onSubmit()">
  <input type="text" name ="user" [formControlName]="'username'" 
  class="form-control" required>
<form>

以上作为登录用户名/电子邮件的示例。 另外，正如评论中提到的，您的 HTML 表单中有一个拼写错误。

当您尝试访问 from 组的 valid 和 invalid 属性时，这应该是有效的。如果有任何问题请评论。

Here is the Angular documentation for reactive forms .