Typescript Angular4 异常：无法绑定到ngClass，因为它不是输入的已知属性

在我的项目中，我使用延迟加载，所以在我的注册模块中，当formGroup在我的注册表单上有一些验证错误时，我使用[ngClass]指令添加无效类.但我的代码在试图在表单上添加[ngClass]指令时抛出了一个异常.

无法绑定到"ngClass"，因为它不是"input"的已知属性

在调查错误本身时，我找到了几种解决方案，比如在组件中添加"directive:[NgStyle]"，但这并不能解决问题.

这是我的代码:

register.router.ts

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { RegisterComponent } from "app/modules/register/register.component";


const routes: Routes = [
{
    path: '', pathMatch: 'full',
    component: RegisterComponent
}
];

@NgModule({
    imports: [
    RouterModule.forChild(routes),
    FormsModule,
    ReactiveFormsModule
],
declarations: [RegisterComponent],
    exports: [RouterModule]
})
export class RegisterRouter { }

register.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { RegisterRouter } from './register.router';  


@NgModule({
    imports: [
      CommonModule,
      RegisterRouter
],
    declarations: []
})
export class RegisterModule { }

register.component.ts

import { Component, OnInit, ViewContainerRef } from '@angular/core';
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 {

//#region Declarations
    UserForm: FormGroup;
    inValid: boolean = false;
//#endregion

constructor(
    private _fb: FormBuilder) { 
    this.UserForm =  _fb.group({
    "_firstname" : ['', Validators.required]
    });
}
}

register.component.html

<input type="text" class="form-control" [ngClass]="{'ahinValid': inValid}" id="txtFirst_Name" aria-describedby="ariaFirstName" placeholder="Enter First Name"
          name="_firstname" [formControl]="UserForm.controls['_firstname']">

谢谢你的帮助.