Angular 6:如何在*ngIf中随机显示元素(Math.random() )

<div *ngIf="showElement1">Element 1</div>
<div *ngIf="showElement2">Element 2</div>
<div *ngIf="showElement3">Element 3</div>

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

@Component({
  selector: 'app-random-elements',
  templateUrl: './random-elements.component.html',
  styleUrls: ['./random-elements.component.css']
})
export class RandomElementsComponent {
  showElement1: boolean;
  showElement2: boolean;
  showElement3: boolean;

  constructor() {
    this.showRandomElement();
  }

  showRandomElement() {
    const randomNumber = Math.floor(Math.random() * 3) + 1;

    this.showElement1 = randomNumber === 1;
    this.showElement2 = randomNumber === 2;
    this.showElement3 = randomNumber === 3;
  }
}

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

import { AppComponent } from './app.component';
import { RandomElementsComponent } from './random-elements/random-elements.component';

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

<app-random-elements></app-random-elements>