将代码移动到函数中时，React-leaflet LayersControl 抛出错误

Question

Sorry if it this has been answered somewhere else before! I am new to react-leaflet and struggle with this issue for some time now.

The following code does not compile and and the chrome developer tools tell me: 3 errors on this page:
1) "TypeError: addOverlay is not a function",
2) "TypeError: addOverlay is not a function" and ",
3) "TypeError: this.props.removeLayer is not a function".

What I do not understand is: if I comment out the "TestOverlay" component, it compiles. There seems to happen some magic with putting the code into a function, but I have no clue what is the problem..

Using: "leaflet": "1.7.1", "react": "16.14.0", "react-dom": "16.14.0", "react-leaflet": "2.7.0",

Thanks a lot for the help!

import React from "react";
import { Map, TileLayer, LayersControl, Marker, LayerGroup } from "react-leaflet";

import "./App.css";

function TestOverlay() {
  return <LayersControl.Overlay checked name="Random layer 2">
  <Marker position={[52.339545, 4.900526]} />
</LayersControl.Overlay>;

}

export default function App() {
  return (
    <Map center={[52.339545, 4.900526]} zoom={14}>
      <TileLayer
        url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
        attribution='&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
      />
      <LayersControl position="topright">
        <LayersControl.Overlay checked name="Random layer">
          <Marker position={[52.339545, 4.900526]} />
        </LayersControl.Overlay>
        <TestOverlay/>
      </LayersControl>
    </Map>);
}

Answer 1

From the documentation1 , documentation2

Map: top-level component instantiating a Leaflet map and providing it to its children.

All components are React wrappers for Leaflet elements and layers, they need a map instance and therefore must be included in a top-level component.

LayersControl.Overlay uses Overlay class( doc ) and inside Overlay class there is the following code:

 class Overlay extends ControlledLayer {
  constructor(props: ControlledLayerProps) {
    super(props)
    this.contextValue = {
      ...props.leaflet,
      layerContainer: {
        addLayer: this.addLayer.bind(this),
        removeLayer: this.removeLayer.bind(this),
      },
    }
  }

  addLayer = (layer: Layer) => {
    this.layer = layer // Keep layer reference to handle dynamic changes of props
    const { addOverlay, checked, name } = this.props
    addOverlay(layer, name, checked)
  }
}

in the constructor addLayer is assigned a method which is this.addLayer . inside this.addLayer addOverlay is being destructured via props. Most likely at that point props do not contain addOverlay method and therefore cannot be retrieved so the error occurs.

As a result you cannot use LayersControl.Overlay the way you are trying to. There is not such an example and I think it is not possible as the map instance is not provided the way it should to LayersControl.Overlay