_co.add is not a function.how to solve this?

Ionic Framework ionic-v3
1

Register Form

		<div padding>
			<button ion-button color="success" size="large" block (click)="addfn()">Register</button>
		</div>
	</ion-col>
</ion-row>

import { NgModule } from ‘@angular/core’;
import { CommonModule } from ‘@angular/common’;
import { FormsModule } from ‘@angular/forms’;
import { Routes, RouterModule } from ‘@angular/router’;

import { IonicModule } from ‘@ionic/angular’;

import { RegisterPage } from ‘./register.page’;

const routes: Routes = [
{
path: ‘’,
component: RegisterPage
}
];

@NgModule({
imports: [
CommonModule,
FormsModule,
IonicModule,
RouterModule.forChild(routes)
],
declarations: [RegisterPage]
})
export class RegisterPageModule {
user_name: string ="";

constructor(public  navCtrl: IonicModule)
{
	
}
addfn():void
{
console.log(this.user_name);
}

}