title: Why ion-router-outlet not working ionic 4
body: <p>I have <code>app.component.html</code></p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;ion-app&gt;
    &lt;ion-split-pane&gt;
      &lt;ion-menu&gt;
        &lt;ion-header&gt;
          &lt;ion-toolbar&gt;
            &lt;ion-title&gt;Menu&lt;/ion-title&gt;
          &lt;/ion-toolbar&gt;
        &lt;/ion-header&gt;
        &lt;ion-content&gt;
          &lt;ion-list&gt;
            &lt;ion-menu-toggle auto-hide="false" *ngFor="let p of appPages"&gt;
              &lt;ion-item [routerDirection]="'root'" [routerLink]="[p.url]"&gt;
                &lt;ion-icon slot="start" [name]="p.icon"&gt;&lt;/ion-icon&gt;
                &lt;ion-label&gt;
                  {{p.title}}
                &lt;/ion-label&gt;
              &lt;/ion-item&gt;
            &lt;/ion-menu-toggle&gt;
          &lt;/ion-list&gt;
        &lt;/ion-content&gt;
      &lt;/ion-menu&gt;
      &lt;ion-router-outlet main&gt;&lt;/ion-router-outlet&gt;
    &lt;/ion-split-pane&gt;
  &lt;/ion-app&gt;
  </code></pre>
  
  <p>also I have <code>detail.page.html</code></p>
  
  <pre class="lang-html prettyprint-override"><code>    &lt;ion-content padding&gt;
        &lt;div *ngIf="invoiceDetailData$ | async as invoiceDetailData"&gt;
          &lt;div *ngFor="let item of invoiceDetailData?.invoiceDetail?.items"&gt;
            &lt;ion-label *ngFor="let child of item.children"&gt;
              {{child.cardName}}
              {{child.availableBalance}}
              {{child.cardNumber}}
            &lt;/ion-label&gt;
          &lt;/div&gt;
        &lt;/div&gt;
        &lt;div&gt;
          &lt;button *ngFor="let pages of detailPages"&gt;
            &lt;span [routerLink]="[pages.url]"&gt;{{pages.title}}&lt;/span&gt;
          &lt;/button&gt;
        &lt;/div&gt;
      &lt;/ion-content&gt;
  
      &lt;ion-router-outlet&gt;&lt;/ion-router-outlet&gt;
  &lt;/ion-app&gt;
  </code></pre>
  
  <p><code>ion-router-outlet</code> not working, but in router the value is pushed. And ref is not clickable                                                                                                                                                                                                                                                                                                                   !              </p>