angular怎么创建声明（使用Angular CDK实现一个Service弹出Toast组件功能）

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

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

<li class="q-toast">
    <li class="q-toast-mask"></li>
    <p class="q-toast-msg">{{msg}}</p>
</li>

.q-toast {
  padding: .2rem .5rem;
  width: 5rem;
  position: relative;
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
  

  .q-toast-mask {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: #000;
    opacity: .8;
    border-radius: 2rem;
  }

  .q-toast-msg {
    color: white;
    z-index: 999;
  }
}

import { Overlay, OverlayConfig } from '@angular/cdk/overlay';
import { ComponentPortal } from '@angular/cdk/portal';
import { Injectable, InjectionToken, Injector } from '@angular/core';
import { ToastComponent } from './toast.component';

@Injectable({
  providedIn: 'root'
})
export class ToastService {

  constructor(private overlay: Overlay) { }

  Show(msg: string) {
    const config = new OverlayConfig();
    const positionStrategy = this.overlay.position()
      .global().centerVertically().centerHorizontally();
    config.positionStrategy = positionStrategy;
    let overlayRef = this.overlay.create(config);
    const inject = Injector.create({
      providers: [
        {
          provide: Toast_Ref,
          useValue: overlayRef
        },
        {
          provide: Toast_Msg,
          useValue: msg
        }
      ]
    })
    console.log(inject.get<string>(Toast_Ref))
    let partal = new ComponentPortal(ToastComponent, null, inject);
    overlayRef.attach(partal)
    setTimeout(() => {
      overlayRef.detach()
      overlayRef.dispose();
    }, 2000);
  }

}

export const Toast_Ref = new InjectionToken<{}>('Toast_Ref');
export const Toast_Msg = new InjectionToken<{}>('Toast_Msg');

export class AppComponent {
  constructor(private toast:ToastService) {
  }
  test() {

    this.toast.Show('hello cdk!')
  }
}