Switch themes in angular material 5

Here's an alternative solution for Angular 5.1+/Angular Material 5.0+.

*Edit: As noted, this still works in Angular 7+.

Working editable example - https://stackblitz.com/edit/dynamic-material-theming

In theme.scss, include a default theme(notice it isn't kept under a class name - this is so Angular will use it as the default), and then a light and dark theme.

theme.scss

@import '~@angular/material/theming';
@include mat-core();

// Typography
$custom-typography: mat-typography-config(
  $font-family: Raleway,
  $headline: mat-typography-level(24px, 48px, 400),
  $body-1: mat-typography-level(16px, 24px, 400)
);
@include angular-material-typography($custom-typography);

// Default colors
$my-app-primary: mat-palette($mat-teal, 700, 100, 800);
$my-app-accent:  mat-palette($mat-teal, 700, 100, 800);

$my-app-theme: mat-light-theme($my-app-primary, $my-app-accent);
@include angular-material-theme($my-app-theme);

// Dark theme
$dark-primary: mat-palette($mat-blue-grey);
$dark-accent:  mat-palette($mat-amber, A200, A100, A400);
$dark-warn:    mat-palette($mat-deep-orange);

$dark-theme:   mat-dark-theme($dark-primary, $dark-accent, $dark-warn);

.dark-theme {
  @include angular-material-theme($dark-theme);
}

// Light theme
$light-primary: mat-palette($mat-grey, 200, 500, 300);
$light-accent: mat-palette($mat-brown, 200);
$light-warn: mat-palette($mat-deep-orange, 200);

$light-theme: mat-light-theme($light-primary, $light-accent, $light-warn);

.light-theme {
  @include angular-material-theme($light-theme)
}

In the app.component file, include OverlayContainer from @angular/cdk/overlay. You can find Angular's documentation for this here https://material.angular.io/guide/theming; though their implementation is a little different. Please note, I also had to include OverlayModule as an import in app.module as well.

In my app.component file, I also declared @HostBinding('class') componentCssClass; as a variable, which will be used to set the theme as a class.

app.component.ts

import {Component, HostBinding } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { OverlayContainer} from '@angular/cdk/overlay';

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

  constructor(public overlayContainer: OverlayContainer) {}

  @HostBinding('class') componentCssClass;

  onSetTheme(theme) {
    this.overlayContainer.getContainerElement().classList.add(theme);
    this.componentCssClass = theme;
  }

}

app.module.ts

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

import { HttpClientModule } from '@angular/common/http';

import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { MatCardModule } from '@angular/material/card';
import { MatButtonModule } from '@angular/material/button';

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

import { OverlayModule} from '@angular/cdk/overlay';

@NgModule({
  declarations: [
    AppComponent,
  ],
  imports: [
    BrowserModule,
    HttpClientModule,
    BrowserAnimationsModule,
    MatCardModule,
    MatButtonModule,
    OverlayModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

Finally, call the onSetTheme function from your view.

app.component.html

<button mat-raised-button color="primary" (click)="onSetTheme('default-theme')">Default</button>
<button mat-raised-button color="primary" (click)="onSetTheme('dark-theme')">Dark</button>
<button mat-raised-button color="primary" (click)="onSetTheme('light-theme')">Light</button>

You might consider using an observable so that the functionality would be more dynamic.