Angular 2表单验证错误"未处理的承诺拒绝:无法分配给引用或变量!"

Question

App.component.html

<div class="container">
  <h2>Form Validation</h2>
  <form>
<div class="form-group">
  <label for="prettyName">Name</label>
  <input type="text" class="form-control" id="prettyName" required minlength="4" maxlength="20" [(ngModel)]="prettyName" name="prettyName" #name="ngModel">
  <div *ngIf="name.errors && (name.dirty || name.touched)" class="alert alert-danger">
    <div [hidden]="!name.errors.required">
      Name is required
    </div>
    <div [hidden]="!name.errors.minlength">
      Name must be at least 4 characters long
    </div>
    <div [hidden]="!name.errors.maxlength">
      Name cannot be more than 20 characters long
    </div>
  </div>
</div>
    <button type="submit" class="btn btn-default">Submit</button>
  </form>
</div>
// ... (Same things for username, email and password)

App.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
 prettyName: string;
  username: string;
  email: string;
  password: string;
}

我遵循了有关表单验证的官方文档:https://angular.io/docs/ts/latest/cookbook/form-validation.html#!#template1

有谁知道这个错误来自哪里？

干杯

Answer 1

您应该更改组件变量或模板#name变量.他们碰撞了:

export class AppComponent {
  prettyname: string; // here
  username: string;
  email: string;
  password: string;
}

也改变你String的string

<form>
  <div class="form-group">
    <label for="prettyName">Name</label>
    <input type="text" class="form-control" id="prettyName" required minlength="4" maxlength="20" [(ngModel)]="prettyName" name="prettyName" #name="ngModel">
    <div *ngIf="name.errors && (name.dirty || name.touched)" class="alert alert-danger">
      <div [hidden]="!name.errors.required">
        Name is required
      </div>
      <div [hidden]="!name.errors.minlength">
        Name must be at least 4 characters long
      </div>
      <div [hidden]="!name.errors.maxlength">
        Name cannot be more than 20 characters long
      </div>
    </div>
  </div>
<button type="submit" class="btn btn-default">Submit</button>

Answer 2

当您尝试使用与现有变量相同的名称定义模板引用变量时，会发生此错误，例如在这种情况下：

    @Component({
    selector: 'example',
    template: `
       <label for="name">Name</label>
       <input type="text" [(ngModel)]="name" #name="ngModel" >
       `
    })
   export class AppComponent {
     name:string;

 }

如您所见，输入中有模板引用变量#name，我的类中有一个名为 name 的变量，当您尝试运行应用程序时，这将导致以下错误：

   zone.js:355 Unhandled Promise rejection: Cannot assign to a 
   reference or variable! ; Zone: <root> ; Task: Promise.then ; Value: 
   Error: Cannot assign to a reference or variable!(…) Error: Cannot 
   assign to a reference or variable!

解决方案是更改变量之一的名称。