如何让ng2-google-charts在显示前等待数据加载？

import { Component, OnInit } from '@angular/core';
import { DataService } from 'path-to-data-service';

@Component({
  selector: 'app-chart',
  templateUrl: './chart.component.html',
  styleUrls: ['./chart.component.css']
})
export class ChartComponent implements OnInit {
  isLoading: boolean = true;
  chartData: any;

  constructor(private dataService: DataService) { }

  ngOnInit() {
    this.loadData();
  }

  loadData() {
    this.dataService.getChartData().subscribe(data => {
      this.chartData = data;
      this.isLoading = false;
    });
  }
}

<div *ngIf="isLoading">正在加载数据...</div>
<google-chart *ngIf="!isLoading" [data]="chartData"></google-chart>