The functionality of an Angular application may be compromised if the necessary modules are not properly imported into

I've noticed some strange behavior in my code recently and I can't figure out where it's originating from. In an effort to clean up my codebase, I decided to create separate modules for each component and a routing module to manage all the routes.

app-routing.module.ts

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';

import { LoginComponent } from '@features/authentication/login/login.component';

const appRoutes: Routes = [
    {
        path     : 'auth/login',
        component: LoginComponent
    },
];

@NgModule({
    imports : [
        RouterModule.forRoot(appRoutes),
    ],
    exports : [
        RouterModule
    ]
})
export class AppRoutingModule { }

login.module.ts

import { NgModule } from '@angular/core';
import { RouterModule } from '@angular/router';
import { MatFormFieldModule} from '@angular/material/button';

import { LoginComponent } from './login.component';

@NgModule({
    declarations: [
        LoginComponent
    ],
    imports     : [
        RouterModule,
        MatFormFieldModule,
    ]
})
export class LoginModule
{
}

Within app.module.ts, I simply import app-routing.module.ts. However, I keep encountering an error stating that

'mat-form-field' is not a known element
. Strangely enough, if I import login.module.ts into app-routing.module.ts, everything works smoothly. It's puzzling as to why this additional step is necessary...

Edit: (app.module.ts)

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

import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

import { CoreModule } from '@core/core.module';
import { LayoutModule } from 'app/layout/layout.module';
import { AppRoutingModule } from './app-routing.module'

import { AppComponent } from 'app/app.component';

@NgModule({
    declarations: [
        AppComponent
    ],
    imports     : [
        // Browser
        BrowserModule,
        BrowserAnimationsModule,

        // App modules
        CoreModule,
        LayoutModule,
        AppRoutingModule,
    ],
    bootstrap   : [
        AppComponent
    ]
})
export class AppModule { }

Answer №1

Upon examining the import tree of your modules, the structure appears as follows:

  • AppModule -> (Imports) -> AppRoutingModule -> (Uses) -> LoginComponent
  • LoginModule -> (Declares) -> LoginComponent

Notice how you are Using and Declaring the LoginComponent from two separate branches that are isolated. AppModule is unaware of LoginComponent and therefore does not have access to it.

The LoginComponent is solely declared (and thus accessible) from LoginModule.

If you wish for the LoginComponent to be accessible outside of LoginModule, I recommend exporting it and Importing LoginModule in AppModule to grant access to LoginComponent, altering the tree to look like this:

  • AppModule

    (Imports) -> AppRoutingModule -> (Uses) -> LoginComponent

    (Imports) -> LoginModule -> (Declares/Exports) -> LoginComponent

Now, AppModule acknowledges the declaration of LoginComponent and has access to it, enabling the creation of an instance when necessary for its route.

import { NgModule } from '@angular/core';
import { RouterModule } from '@angular/router';
import { MatFormFieldModule} from '@angular/material/button';

import { LoginComponent } from './login.component';

@NgModule({
    declarations: [
        LoginComponent
     ],
    imports     : [
        RouterModule,
        MatFormFieldModule,
    ],
    exports : [
      LoginComponent
    ]
})
export class LoginModule
{
}

Additionally,

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

import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

import { CoreModule } from '@core/core.module';
import { LayoutModule } from 'app/layout/layout.module';
import { AppRoutingModule } from './app-routing.module'

import { AppComponent } from 'app/app.component';

@NgModule({
    declarations: [
        AppComponent
     ],
    imports     : [
        // Browser
        BrowserModule,
        BrowserAnimationsModule,

        // App modules
        CoreModule,
        LayoutModule,
        AppRoutingModule,

        LoginModule,
     ],
    bootstrap   : [
        AppComponent
    ]
})
export class AppModule { }

Furthermore, depending on your app's specific use case, I highly recommend exploring lazyloading for your modules if they are associated with particular routes https://angular.io/guide/lazy-loading-ngmodules

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