LeafletJS：地图容器已经初始化

Question

I am using Leaflet in my Ionic 2 app. When running the app first time. Everyhting is fine. But if I go to another page and back to the map I get the following exception:

EXCEPTION: Error: Uncaught (in promise): EXCEPTION: Error in build/pages/map/map.html:12:18 ORIGINAL EXCEPTION: Error: Map container is already initialized. ORIGINAL STACKTRACE: Error: Map container is already initialized.

The private variable map is null when coming back to this page. Checking this variable for beeing null has no effect because I think the problem is the new L.Map('mainmap',...

export class MainMapComponent {

  private map;

  constructor(
    private mapService: MapService,
    private geoCodingService: GeocodingService) { }

  ngOnInit() {
    console.log(this.map);
    if( this.map == null ) this.initMap();
  }

  initMap() {
    console.log('init');
    if(this.map) this.map.remove();
    this.map = new L.Map('mainmap', {
      zoomControl: false,
      center: new L.LatLng(40.731253, -73.996139),
      zoom: 12,
      minZoom: 4,
      maxZoom: 19,
      layers: [this.mapService.baseMaps.OpenStreetMap],
      attributionControl: false
    });
    console.log(this.map);
  }

}

Answer 1

Probably not the most elegant solution but what worked for me is removing the map when the user leaves the view:

ionViewCanLeave(){
    document.getElementById("mainmap").outerHTML = "";
}

Source: https://forum.ionicframework.com/t/map-container-is-already-initialized-error-in-ionic-2/81666

Answer 2

The if( this.map == null ) condition in your ngOnInit() is always true , since when you instantiate a new MainMapComponent , that new instance will get its own brand new this.map , therefore unassigned (ie undefined ) yet.

This is totally different from what may have happened to your "mainmap" div container.

To be more inline with your problem description, when navigating away from your map, your "mainmap" div container still holds a map . When coming back to your page, it looks like your app instantiates a new MainMapComponent instance, which has a new (unassigned yet) this.map , therefore it tries to initialize a new map in "mainmap" div container. This is what creates the error.

You could try to use this.map.remove() when your MainMapComponent instance is destroyed, so that the "mainmap" div status is in par with the existence (or not) of an instance of MainMapComponent . But that would not solve your problem if for any reason you have more than one instance of MainMapComponent at the same time.

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Update:

As for the last mentioned issue, see Initializing leaflet map in angular2 component after DOM object exists