Can't access Polygon coordinates after drag with React-Leaflet

Question

I need to access the new coordinates of a Polygon after I have successfully dragged it somewhere else on the map. I am using Leaflet and React-Leaflet. This is my Polygon component:

 <Map
  // ...
 >
   <TileLayer
     attribution='&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
     url="http://{s}.tile.osm.org/{z}/{x}/{y}.png"
   />
     <Polygon
        positions={this.state.polygonCoordinates}
        ref={this._polygon}
        draggable={true}
     />
 </Map>

I have tried:

1. To access the coordinates either in the draggable prop or onChange . Needless to say, this didn't work:

 <Polygon
    positions={this.state.polygonCoordinates}
    ref={this._polygon}
    onChange={(event) => {
      console.log(event);
      console.log(this._polygon.current.leafletElement);
    }}
    draggable={(event) => {
      console.log(event);
      console.log(this._polygon.current.leafletElement);
      return true;
    }}
 />

2. To use componentDidUpdate as I have the state that changes when the polygon is created (I am using lodash ). I am usign mousedown and not onmousedown

componentDidUpdate(prevProps, prevState) {
  if (
    !_.isEqual(prevState.closePolygon, this.state.closePolygon) &&
    this.state.closePolygon
  ) {
    // the polygon is created and closed
    const leafletPolygon = this._polygon.current.leafletElement;
    leafletPolygon.addEventListener("onmousedown", this.movePolygon(event));
  }
}

movePolygon = (event) => {
    console.log(event, this._polygon);
  };

This last approach does not work because it fires the event only once, right after I create the Polygon , and then doesn't fire again when I drag it around and then release the mouse.

TL;DR: the Polygon is correctly moved inside the map, but I can't figure out how to access its new coordinates (positions). Thank you for your help!

Answer 1

I found the solution! I changed a bit the part inside the componentDidUpdate method:

componentDidUpdate(prevProps, prevState) {
    if (
        !_.isEqual(prevState.closePolygon, this.state.closePolygon) &&
        this.state.closePolygon
    ) {
      // the polygon is created and closed
      let element = document.getElementsByClassName("geo-polygon")[0];
      // necessary to access the this keyword inside the callback
      const that = this;
      element.addEventListener("mouseup", function () {
        const newLatLangs = [...that._polygon.current.leafletElement._latlngs];
        that.setState({ polygonCoordinatesAfterMoving: [...newLatLangs] });
      });
  }
}

Now the polygon gets correctly dragged inside the map (as it did before), but I can also save the new coordinates. I am saving them in a new variable as I have yet to optimize this solution, and I don't need to redraw a new polygon on the map with the new coordinates - the draggable={true} Polygon prop works just fine for me.

So, it seemed like I was almost there.