Ionic 2 Error of X page is part of the declarations of 2 modules

问题

I had gone through SO questions over here. But I am Unable to get What this error is trying to suggest. Please Help me out for this.

Lastly, HIGHER MODULE Means which module. As I am new to this That is why Not getting this correctly.

Mycode:

app.module.ts

   @NgModule({
  declarations: [
    MyApp,
    UsersPage,
    ReposPage,
    OrganisationsPage,
    UserDetailsPage,
    LoginPage

  ],
  imports: [

    BrowserModule,
    HttpModule,
    IonicModule.forRoot(MyApp),

  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    LoginPage,
    UsersPage,
    ReposPage,
    OrganisationsPage,
    UserDetailsPage,


  ],

Login.module.ts

import { NgModule } from '@angular/core';
import { IonicPageModule,IonicPage } from 'ionic-angular';
import { LoginPage } from './login';
//import { IonicPage } from 'ionic-angular';

@IonicPage()
@NgModule({
  declarations: [
    LoginPage,
  ],
  imports: [
    IonicPageModule.forChild(LoginPage),
  ],
  entryComponents: [
    LoginPage
  ],
  exports: [
    LoginPage
  ]
})
export class LoginPageModule {}

UPDATED CODE AS PER YOUR COMMENT

app.module.ts

import { Component } from '@angular/core';
import { NavController, AlertController, LoadingController, Loading, IonicPage } from 'ionic-angular';
import { AuthService } from '../../providers/auth-service';


@IonicPage()
@Component({
  selector: 'page-login',
  templateUrl: 'login.html',
})
export class LoginPage {
  loading: Loading;
  registerCredentials = { email: '', password: '' };

  constructor(private nav: NavController, private auth: AuthService, private alertCtrl: AlertController, private loadingCtrl: LoadingController) { }

  public createAccount() {
    this.nav.push('RegisterPage');
  }

  public login() {
    this.showLoading()
    this.auth.login(this.registerCredentials).subscribe(allowed => {
      console.log(allowed)
      if (allowed) {        
        this.nav.setRoot('HomePage');
      } else {
        this.showError("Access Denied");
      }
    },
      error => {
        this.showError(error);
      });
  }

  showLoading() {
    this.loading = this.loadingCtrl.create({
      content: 'Please wait...',
      dismissOnPageChange: true
    });
    this.loading.present();
  }

  showError(text) {
    this.loading.dismiss();

    let alert = this.alertCtrl.create({
      title: 'Fail',
      subTitle: text,
      buttons: ['OK']
    });
    alert.present(prompt);
  }
}

login.module.ts

import { NgModule } from '@angular/core';
import { IonicPageModule,IonicPage } from 'ionic-angular';
import { LoginPage } from './login';
//import { IonicPage } from 'ionic-angular';


@NgModule({
  declarations: [
    LoginPage,
  ],
  imports: [
    IonicPageModule.forChild(LoginPage),
  ],
  entryComponents: [
    LoginPage
  ],
  exports: [
    LoginPage
  ]
})
export class LoginPageModule {}

login.ts

import { Component } from '@angular/core';
import { NavController, AlertController, LoadingController, Loading, IonicPage } from 'ionic-angular';
import { AuthService } from '../../providers/auth-service';


@IonicPage()
@Component({
  selector: 'page-login',
  templateUrl: 'login.html',
})
export class LoginPage {
  loading: Loading;
  registerCredentials = { email: '', password: '' };

  constructor(private nav: NavController, private auth: AuthService, private alertCtrl: AlertController, private loadingCtrl: LoadingController) { }

  public createAccount() {
    this.nav.push('RegisterPage');
  }

  public login() {
    this.showLoading()
    this.auth.login(this.registerCredentials).subscribe(allowed => {
      console.log(allowed)
      if (allowed) {        
        this.nav.setRoot('HomePage');
      } else {
        this.showError("Access Denied");
      }
    },
      error => {
        this.showError(error);
      });
  }

  showLoading() {
    this.loading = this.loadingCtrl.create({
      content: 'Please wait...',
      dismissOnPageChange: true
    });
    this.loading.present();
  }

  showError(text) {
    this.loading.dismiss();

    let alert = this.alertCtrl.create({
      title: 'Fail',
      subTitle: text,
      buttons: ['OK']
    });
    alert.present(prompt);
  }
}

回答1:

I assume you're using the Lazy Load feature of Ionic. What that error means, is that you're including the LoginPage in the declarations array of the NgModule both in the AppModule (app.module.ts file) and the LoginPageModule.

In order to fix it, remove the LoginPage declaration of the AppModule, and if you need to use the LoginPage somewhere in the app (for instance, if you want to push that page), use the name but as a string, like this:

// Somewhere in your app
this.navCtrl.push('LoginPage'); // <- The name of the page is used as a string

Since the name of the page is now a string, you won't need to import the LoginPage anymore

// import { LoginPage } from '/path/to/login-page.ts'; <- You won't need to do this anymore

---

UPDATE

Just like you can see in the docs (thanks @suraj), please check that you're creating the module of the LoginPage like this:

@NgModule({
  declarations: [
    MyPage
  ],
  imports: [
    IonicPageModule.forChild(MyPage)
  ],
  entryComponents: [
    MyPage
  ]
})
export class MyPageModule {}

And also check that you're adding the @IonicPage() decorator to the page:

// Ionic
import { IonicPage } from 'ionic-angular';

@IonicPage()
@Component({...})
export class MyPage {}

来源：https://stackoverflow.com/questions/44630233/ionic-2-error-of-x-page-is-part-of-the-declarations-of-2-modules