ion 2- <ion-segment> <div>谷歌地图未显示

Question

加载页面时，将显示google地图。但是，当离子段被切换时，贴图不会显示。下面是我的ionic 2代码：

<ion-header>
  <ion-toolbar no-border-top>
    <ion-segment [(ngModel)]="social" (ionChange)="segementChangeAction()">
      <ion-segment-button value="activity">
        Map
      </ion-segment-button>
      <ion-segment-button value="messages">
        Messages
      </ion-segment-button>
    </ion-segment>
  </ion-toolbar>
</ion-header>



<ion-content no-bounce>
  <div [ngSwitch]="social">
    <div *ngSwitchCase="'activity'">
        <div #map id="map"></div>
    </div>
    <div *ngSwitchCase="'messages'">
      Some text.....        
    </div>
  </div>
</ion-content>