Error

[Solved] Error NG8001: ‘Mat-Form-Field’ Is Not a Known Element in Angular CLI

Hey angular geek, if you have the Error NG8001: ‘Mat-Form-Field’ Is Not a Known Element in Angular, you are at the correct place to find the solution.

I was developing a mini project using Angular 9 at the front-end with the Angular material theme. I was a novice to the Angular at that time.

After some development, I tried to put a form field in a dialog box of an angular material theme. However, my code was not working out. The material theme was not applying to the input field I added to the dialog box. Even more, I was having an error that Mat-Form-Field is not a known element.

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Error NG8001: Is Not a Known Element

The above error for any angular element occurs when we forget to import that element directives from the angular source to our working component.ts file.

However, when I tried to debug, I found that the input skin of the angular material theme was applied to the app.module.html file. And the same input field code was not working inside the dialog file.

But, I have already imported all the necessary components from the angular material directive. My code was as mentioned below.

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app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent, GetStartedDialog } from './app.component';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

import {MatToolbarModule} from '@angular/material/toolbar';
import {MatButtonModule} from '@angular/material/button';
import {MatDialogModule} from '@angular/material/dialog';
import {MatInputModule} from '@angular/material/input';

@NgModule({
  imports: [
    BrowserModule,
    AppRoutingModule,
    BrowserAnimationsModule,
    MatToolbarModule,
    MatButtonModule,
    MatDialogModule,
    MatInputModule
  ],
  declarations: [
    AppComponent
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

As you can see, all the necessary components are already imported in the app.module.ts file.

app.component.ts

import { Component } from '@angular/core';
import {MatDialog, MatDialogRef} from '@angular/material/dialog';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent {
  
  constructor(public dialog: MatDialog) {}

  openDialog(): void {
    const dialogRef = this.dialog.open(GetStartedDialog, {
      width: '300px'
    });

    dialogRef.afterClosed().subscribe(result => {
      console.log('The dialog was closed');
    });
  }
}

@Component({
  selector: 'get-started-dialog',
  templateUrl: 'get-started-dialog.html',
})
export class GetStartedDialog {

  constructor(
    public dialogRef: MatDialogRef) {}

  onNoClick(): void {
    this.dialogRef.close();
  }

}

app.component.ts

<section class="mat-typography">
  <div>
    <button mat-raised-button color="primary" (click)="openDialog()">Get Started</button>
  </div>
</section>

get-started-dialog.html

<div mat-dialog-content style="text-align: center;">
    <h3 class="text-accent">Dialog</h3>
    <hr>
    <p>Enter your details.</p>
    <br>
    <mat-form-field class="full-width">
        <mat-label>Name</mat-label>
        <input matInput placeholder="Enter Your Full Name">
    </mat-form-field>
</div>

Solution

After some hours of research and debugging, I found that the angular generates dynamic content inside the dialog element.

So we have to add the dialog box class at declarations and entryComponents in the @NgModule in our module.ts file. My app.module.ts file was as follows after the change.

Updated app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent, GetStartedDialog } from './app.component';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

import {MatToolbarModule} from '@angular/material/toolbar';
import {MatButtonModule} from '@angular/material/button';
import {MatDialogModule} from '@angular/material/dialog';
import {MatInputModule} from '@angular/material/input';

@NgModule({
  imports: [
    BrowserModule,
    AppRoutingModule,
    BrowserAnimationsModule,
    MatToolbarModule,
    MatButtonModule,
    MatDialogModule,
    MatInputModule
  ],
  declarations: [
    AppComponent,
    GetStartedDialog
  ],
  entryComponents: [
    GetStartedDialog
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

Explanation

As you can see, I added the GetStartedDialog class inside declarations and entryComponents, which helps the dialog box to compile its inside angular components/elements at the runtime.