How to write a component which outputs Markers?

[varya]

How a custom react component which outputs Marker on map should be written? I need to have smth like this working:

import MyMarker from './MyMarker.js';

const builtMarker = (function() {
  const position = [51.520, -0.11];
  return (
    <MyMarker position={position}/>
  );
})();

render(
  <div>
    <h1>Hello, world!</h1>
    <div className="map">
        <Map center={center} zoom={13}>
            <TileLayer
            url='http://{s}.tile.osm.org/{z}/{x}/{y}.png'
            attribution='&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
            />
            {builtMarker}
        </Map>
    </div>
  </div>
  ,
  document.getElementById('example')
);

I made MyMarker component like that https://github.com/varya/react-leaftlet-test/blob/master/src/MyMarker.js but this gets error:

Uncaught TypeError: Cannot read property 'addLayer' of undefined

I guess the component should not only extend MapLayer but also provide special interface. What is missing? I could not find similar example in the docs.

Also, what should I do to output several Markers? I mean, in React it's required to be in a single wrapper. But it cannot be just <div> for the map. How this wrapper should be written?

PS: This is the repo where I demonstrate my case https://github.com/varya/react-leaftlet-test

[surkova]

I don't know if it's the right approach in React world, but I did the following and it worked:

import React, {Component} from 'react';
import {Marker, Popup} from 'react-leaflet';

class MyMarker extends Marker {

  componentWillMount() {
    super.componentWillMount();
  }

  render () {
    return (
        <Marker position={this.props.position}>
            <Popup>
                <span>A pretty CSS3 popup.<br/>Easily customizable.</span>
            </Popup>
        </Marker>
    )
  }
}

export default MyMarker;

You were simply missing map, that's passed via const { map, position, ...props } = this.props; in Marker.js

[varya]

@surkova, this does not help. But I updated the repo with componentWillMount anyway, just to demonstrate that this does not work.

[surkova]

Then yet another suggestion:

import React, {Component} from 'react';
import {marker} from 'leaflet';
import {MapLayer} from 'react-leaflet';

class MyMarker extends MapLayer {
  componentWillMount() {
    super.componentWillMount();
    const { map, position, popupText, ...props } = this.props;
    this.leafletElement = marker(position, props).bindPopup(popupText);
  }
  render() {
    return this.renderChildrenWithProps({
      layerGroup: this.leafletElement,
    });
  }
}

export default MyMarker;

const builtMarker = (function() {
  const position = [51.520, -0.11];
  const popupText = "A pretty CSS3 popup.<br/>Easily customizable."
  return (
    <MyMarker position={position} popupText={popupText}/>
  );
})();

[varya]

Thank you very much, but the point is to use Marker react component. Of course it's possible to create markers on the low level, but then the usage of react-leaflet doesn't make any sense.

[PaulLeCam]

As written in the documentation, you need to pass the map property injected by the <Map> component to children components.

Ex:

const MyMarker = ({ map, position }) => (
  <Marker map={map} position={position}>
    <Popup>
      <span>A pretty CSS3 popup.<br/>Easily customizable.</span>
    </Popup>
  </Marker>
);

...

<Map center={center} zoom={13}>
  <TileLayer
    url='http://{s}.tile.osm.org/{z}/{x}/{y}.png'
    attribution='&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors'
  />
  <MyMarker position={position} />
</Map>

[varya]

@PaulLeCam, thank you for the answer. This example works. But I'm also wondering how to insert a variable or a set of Markers. This would be nice to have an example in examples with a custom component which outputs a list of markers. I think many will be clear from such an example.

[PaulLeCam]

What do you mean by variable and set of markers?
At this point it is just React, so you can apply usual patterns that work with it.

Ex:

const MyPopupMarker = ({ map, position, children }) => (
  <Marker map={map} position={position}>
    <Popup>
      <span>{children}</span>
    </Popup>
  </Marker>
);

const MyMarkersList = ({ map, markers }) => {
  const items = markers.map(({ key, ...props }) => (
      <MyPopupMarker key={key} map={map} {...props} />
  ));
  return <div style={{display: 'none'}}>{items}</div>;
};

...

class MyMap extends Component {
  ...
  render() {
    // Probably generated dynamically, but the logic is the same                            
    const markers = [
      {key: 'marker1', position: [51.5, -0.1], children: 'My first popup'},
      {key: 'marker2', position: [51.51, -0.1], children: 'My second popup'},                  
    ];

    return (
      <Map ...>
        <TileLayer .../>
        <MyMarkersList markers={markers} />
      </Map>
    );
  }
}

The only constraint if you want to render a list in a component is to wrap it in a container, this is purely a React constraint.
In our case having Leaflet actually render the layers, a possible solution is to wrap them in a div with display: none.

[varya]

Thank you very much! Now it's clear.
I made a pull request with this code into your set of examples. This is the place where I was looking for an answer before asked here. Maybe someone else will also look there :-)
#104

[PaulLeCam]

Glad it helps!
Thanks for your PR, I'll merge it.

[taozhi8833998]

map and layerContainer is not passed to child componet in react-leaflet 1.1.1 version ???

[felixsonyusuftosin]

I have set up map like this

render(){
     return(
    <Map  className="markercluster-map"  ref = "map" maxZoom = {30} minZoom ={2} center={this.props.markers[0].position}  zoom={9}>
          <BingTileLayer url = '' bingKey='<bingmapskey>'  type='aerial' />
           {
            this.props.markers?
              <MarkerClusterGroup   wrapperOptions={{enableDefaultStyle: true}}  >
                 <GeoJSON    ref='geojd' data = {this.geoj}  onEachFeature = {this.onEachDot }/>
            </MarkerClusterGroup>
            :
            null
        }



      </Map>
     ) }

What i require is to have access to my GeoJSON Layer via

componentDidMount(){
let th = this;
this.map = this.refs.map.leafletElement;

   this.geojson = this.refs.geojd.leafletElement 
        console.log(this.geojson);           
    
     }

[topgun743]

I have a question in this regard.
I have 20 different sets of markers, with each set comprising of minimum 50 markers (in production may be much more than that).
In my current application when I iterate over these sets of markers for rendering, it freezes my UI causing frustration to the end user.

How can I render these sets on leaflet map asynchronously. What is the best approach?
And also, can the leaflet map L.map instance be approached by multiple simultaneously executing blocks of code?