Can't bind to 'ngModel' since it isn't a known property of 'input'

angular2在双向数据绑定时[(ngModel)]无法使用，出现的错误是：

Can't bind to 'ngModel' since it isn't a known property of 'input'.

解决办法：

在文件 app.component.ts 中引入ngModel

具体为：

添加两行代码：

import { FormsModule } from '@angular/forms';

和

FormsModule,