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bluehalo / ngx-leaflet

Core Leaflet package for Angular.io
MIT License
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@bluehalo/ngx-leaflet

Build Status

Leaflet packages for Angular.io. Provides flexible and extensible components for integrating Leaflet v0.7.x and v1.x into Angular.io projects. Supports Angular v18 and use in Angular-CLI based projects.

NOTE: This is the last version of this package that will be published under the @asymmetrik namespace. This and future versions will be published under the namespace: @bluehalo

Table of Contents

Install

Install the package and its peer dependencies via npm (or yarn):

npm install leaflet
npm install @bluehalo/ngx-leaflet

If you intend to use this library in a typescript project (utilizing the typings), you'll need to install the leaflet typings:

npm install --save-dev @types/leaflet

If you want to run the demo, clone the repository, perform an npm install, npm run demo and then go to http://localhost:4200

Not using the latest version of Angular.io? Have a look in CHANGES.md to find the right version for your project.

Usage

To use this library, there are a handful of setup steps to go through that vary based on your app environment (e.g., Webpack, ngCli, SystemJS, etc.). Generally, the steps are:

Import the Leaflet Stylesheet

For leaflet to work, you need to have the leaflet stylesheets loaded into your application. If you've installed via npm, you will need to load ./node_modules/leaflet/dist/leaflet.css. How you include the stylesheet will depend on your specific setup. Here are a few examples:

Direct Import from HTML

If you are just building a webpage and not using a bundler for your css, you'll want to directly import the css file in your HTML page.

<head>
    ...
    <link rel="stylesheet" type="text/css" href="https://github.com/bluehalo/ngx-leaflet/blob/master/node_modules/leaflet/dist/leaflet.css">
    ...
</head>

Configuring Webpack Style Loaders

If you are using Webpack, you will need to import the css file and have a style-loader configured. You can use the demo included in this application as a reference.

Generally, in vendor.ts:

import 'leaflet/dist/leaflet.css';

And then in your webpack config file:

{
    ...
    "module" : {
        loaders: [
            ...
            { test: /\.css$/, loaders: [ 'style-loader', 'css-loader' ] },
            ...
        ]   
    },
    ...
}

Adding Styles in Angular CLI

If you are using Angular CLI, you will need to add the Leaflet CSS file to the styles array contained in angular.json

{
    ...
    "styles": [
        "styles.css",
        "./node_modules/leaflet/dist/leaflet.css"
    ],
    ...
}

Import Code Dependencies and Module

This project is exported using UMD and it includes typings. So, you shouldn't have to do anything special to use it if you're building your project in Typescript.

Typescript Angular.io Module Import

Before you can use the module in your Angular.io app, you'll need to import it in your application (and potentially the module that's using it).

For example, in your app.module.ts, add:

import { LeafletModule } from '@bluehalo/ngx-leaflet';

...
imports: [
    ...
    LeafletModule
]
...

Potentially, you'll also need to import it into the module of the component that is going to actually use the ngx-leaflet directives. See Angular.io docs of modules for more details (https://angular.io/guide/ngmodule). In this case, in my-module.module.ts, add:

import { LeafletModule } from '@bluehalo/ngx-leaflet';

...
imports: [
    ...
    LeafletModule
]
...

Not Using Typescript?

You brave soul. The code is exported using UMD. The bundles are generated as part of the build (npm run build) and placed into the ./dist dir. You should be able to import is using whatever module system/builder you're using, even if you aren't using Typescript.

Create and Configure a Map

Once the dependencies are installed and you have imported the LeafletModule, you're ready to add a map to your page. To get a basic map to work, you have to:

Template:

<div style="height: 300px;"
     leaflet 
     [leafletOptions]="options">
</div>

Example leafletOptions object:

options = {
    layers: [
        tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', { maxZoom: 18, attribution: '...' })
    ],
    zoom: 5,
    center: latLng(46.879966, -121.726909)
};

Changes to leafletOptions are ignored after they are initially set. This is because these options are passed into the map constructor, so they can't be changed anyways. So, make sure the object exists before the map is created. You'll want to create the object in ngOnInit or hide the map DOM element with *ngIf until you can create the options object.

Add a Layers Control

The [leafletLayersControl] input bindings give you the ability to add the layers control to the map. The layers control lets the user toggle layers and overlays on and off.

Template:

<div style="height: 300px;"
     leaflet 
     [leafletOptions]="options"
     [leafletLayersControl]="layersControl">
</div>

Example layersControl object:

layersControl = {
    baseLayers: {
        'Open Street Map': tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', { maxZoom: 18, attribution: '...' }),
        'Open Cycle Map': tileLayer('https://{s}.tile.opencyclemap.org/cycle/{z}/{x}/{y}.png', { maxZoom: 18, attribution: '...' })
    },
    overlays: {
        'Big Circle': circle([ 46.95, -122 ], { radius: 5000 }),
        'Big Square': polygon([[ 46.8, -121.55 ], [ 46.9, -121.55 ], [ 46.9, -121.7 ], [ 46.8, -121.7 ]])
    }
}

You can add any kind of Leaflet layer you want to the overlays map. This includes markers, shapes, geojson, custom layers from other libraries, etc.

Add Custom Layers (base layers, markers, shapes, etc.)

There are several different ways to add layers to the map. You can add layers (baselayers, markers, or custom layers) to the map without showing them in the layer control using the [leafletLayers] directive.

Template:

<div style="height: 300px;"
     leaflet
     [leafletOptions]="options"
     [leafletLayers]="layers">
</div>

Layers array:

layers = [
    circle([ 46.95, -122 ], { radius: 5000 }),
    polygon([[ 46.8, -121.85 ], [ 46.92, -121.92 ], [ 46.87, -121.8 ]]),
    marker([ 46.879966, -121.726909 ])
];

You can also add an individual layer to the map using the [leafletLayer] directive. Using this approach allows you to use *ngFor and *ngIf to control whether individual layers are added to or removed from the map.

Template:

<div style="height: 300px;"
     leaflet
     [leafletOptions]="options">
     <div *ngIf="showLayer" [leafletLayer]="layer"></div>
</div>

Layer:

layer = circle([ 46.95, -122 ], { radius: 5000 });

Dynamically Change Map Layers using [leafletLayers]

Layer inputs (arrays and maps) are mutable Previous versions of this plugin treated layers arrays and layer control objects as immutable data structures. We've changed that behavior. Now, mutable changes to the leafletLayers, leafletBaseLayers, and leafletLayersControl inputs are detected.

The plugin is now using internal ngx iterable and key/value differs to detect and track changes to mutable data structures. This approach requires a deep compare of the contents of the data structure (which can be slow when the contents are really big). For immutable data structures, all that is needed is a top-level instance equality check (which is way faster). This change is backwards compatible and was motivated by feedback and confusion. While there is a performance impact for some use cases, this approach is more intuitive.

There are at least two good approaches to improving performance when there are a lot of layers bound to the map. First, you can use the OnPush change detection strategy. There's an example of this in the demo. Second, you can wrap a large number of layers into a Leaflet layer group, which will reduce the number of layers the plugin actually has to track during diffs.

Working with Leaflet Events

Often, you'll want to make changes based on a map click or other Leaflet interaction. The ngx-leaflet plugin supports several map events and layer events as documented in the API section.

You may occasionally need to handle events that aren't exposed through the plugin, however. When that happens, you will need to be aware of how Zones and change detection work to ensure your event handling works as expected. Take a look at A Note About Change Detection for more details. This is by design and a common thing to deal with when using third party libraries and Angular.

API

This section includes more detailed documentation of the functionality of the directives included in this library.

Advanced Map Configuration

There are several input bindings available for configuring the map.

<div leaflet style="height: 300px;"
     [leafletOptions]="options"
     [leafletPanOptions]="panOptions"
     [leafletZoomOptions]="zoomOptions"
     [leafletZoomPanOptions]="zoomPanOptions"
     [leafletFitBoundsOptions]="fitBoundsOptions">
</div>

[leafletOptions]

Input binding for the initial leaflet map options (see Leaflet's docs). These options can only be set initially because they are used to create the map. Later changes are ignored.

[leafletPanOptions]

Input binding for pan options (see Leaflet's docs). These options are stored and used whenever pan operations are invoked.

[leafletZoomOptions]

Input binding for zoom options (see Leaflet's docs). These options are stored and used whenever zoom operations are invoked.

[leafletZoomPanOptions]

Input binding for zoom/pan options (see Leaflet's docs). These options are stored and used whenever zoom/pan operations are invoked.

[leafletFitBoundsOptions]

Input binding for FitBounds options (see Leaflet's docs). These options are stored and used whenever FitBounds operations are invoked.

Dynamically changing zoom level, center, fitBounds, etc.

<div leaflet style="height: 300px;"
     [leafletOptions]="options"
     [(leafletZoom)]="zoom"
     [(leafletCenter)]="center"
     [leafletFitBounds]="fitBounds">
</div>

[(leafletZoom)]: number

Input and Output binding for the map zoom level.

[leafletMaxZoom]: number

Input binding for the maximum zoom level for the map.

[leafletMinZoom]: number

Input binding for the minimum zoom level for the map.

[(leafletCenter)]: LatLng

Input and Output binding for the map center position.

Note: center/zoom operations may interfere with each other

Zoom/Center operations that are applied in rapid succession may interfere with or cancel each other. If both changes are picked up at the same time, the component applies the changes as a map.setView() operation to ensure both are processed. Additionally, if a zoom level or center is applied that is not allowed (e.g., beyond max zoom level or outside of max bounds), Leaflet will determine the new value.

[leafletFitBounds]: LatLngBounds

Input bind a LatLngBounds value that will be applied to the map using Map.setFitBounds(). This operation has no output binding because the input fitBounds usually results in a slightly different map bounds.

[leafletMaxBounds]: LatLngBounds

Input bind a LatLngBounds value that will be applied to the map using Map.setMaxBounds().

Simple Layer Management: Setting Baselayers

There is a convenience input binding for setting the baselayers on the map called [leafletBaseLayers]. You can also provide [leafletLayersControlOptions] if you want to show the control on the map that allows you to switch between baselayers. If you plan to show more than just baselayers, you should use the more advanced layers controls described in Advanced Layer Management below.

For an example of the basic map setup, you should check out the Simple Base Layers demo.

<div leaflet style="height: 300px;"
     [leafletOptions]="options"
     [leafletBaseLayers]="baseLayers"
     [leafletLayersControlOptions]="layersControlOptions">
</div>

[leafletBaseLayers]: Control.LayersObject

Input bind an Control.LayersObject to be synced to the map.

baseLayers: {
    'layer1': Layer,
    'layer2': Layer
}

On changes, the component syncs the baseLayers on the map with the layers in this object. Syncing is performed by tracking the current baselayer and on changes, searching the map to see if any of the current baselayers is added to the map. If it finds a baselayer that is still added to the map, it will assume that is still the baselayer and leave it. If none of the baselayers can be found on the map, it will add the first layer it finds in the Control.LayersObject and use that as the new baselayer. Layers are compared using instance equality.

If you use this directive, you can still manually use the [leafletLayers] directive, but you will not be able to use the [leafletLayersControl] directive. This directive internally uses the layers control, so if you add both, they'll interfere with each other. Because it uses control.layers under the hood, you can still provide options for the layers control.

[leafletLayersControlOptions]

Input binding for Control.Layers options (see Leaflet's docs). These options are passed into the layers control constructor on creation.

Advanced Layer Management: Layers, and Layers Control

The [leafletLayers] and [leafletLayersControl] input bindings give you direct access to manipulate layers and the layers control. When the array bound to [leafletLayers] is changed, the directive will synchronize the layers on the map to the layers in the array. This includes tile layers and any added shapes.

The [leafletLayersControl] input binding allows you to provide a set of base layers and overlay layers that can be managed within leaflet using the layers control. When the user manipulates the control via Leaflet, Leaflet will automatically manage the layers, but the input bound layer array isn't going to get updated to reflect those changes.

So, use [leafletLayers] to add a collection of layers to the map. And, use [leafletLayersControl] to allow users to optionally turn layers/overlays on and off.

For an example of using the layers controls, you should check out the Layers and Layer Controls demo.

<div leaflet style="height: 300px;"
     [leafletOptions]="options"
     [leafletLayers]="layers"
     [leafletLayersControl]="layersControl"
     [leafletLayersControlOptions]="layersControlOptions">
</div>

[leafletLayers]: Layer[]

Input bind an array of all layers to be synced (and made visible) in the map.

On changes, the component syncs the layers on the map with the layers in this array. Syncing is performed by selectively adding or removing layers. Layers are compared using instance equality. As a result of how the map is synced, the order of layers is not guaranteed to be consistent as changes are made.

[leafletLayersControl]: Control.Layers

Input bind a Control.Layers specification. The object contains properties for each of the two constructor arguments for the Control.Layers constructor.

layersControl: {
    baseLayers: {
        'layerName': Layer
    },
    overlays: {
        'overlayName': Layer
    }
}

[leafletLayersControlOptions]

Input binding for Control.Layers options (see Leaflet's docs). These options are passed into the constructor on creation.

Advanced Layer Management: Individual Layers and ngFor / ngIf

The [leafletLayer] input bindings gives you the ability to add a single layer to the map. While this may seem limiting, you can nest elements inside the map element, each with a [leafletLayer] input. The result of this is that each layer will be added to the map. If you add a structural directive - *ngFor or *ngIf - you can get some added flexibility when controlling layers. 

<div leaflet style="height: 300px;"
     [leafletOptions]="options">
    <div *ngFor="let l of layers" [leafletLayer]="l"></div>
</div>

In this example, each layer in the layers array will create a new child div element. Each element will have a [leafletLayer] input binding, which will result in the layer being added to the map. For more details, you should check out the Layers and ngFor demo.

There are several layer events that are available when you are using this approach to controlling layers.

Layer Events

When you are using the [leafletLayer] directive to add a layer, you can also access output bindings for layer events. Two events that are currently exposed include: (leafletLayerAdd) and (leafletLayerRemove). Each of these emits a LeafletEvent object.

Map Events

Leaflet exposes a lot of map events including map zoom, map move, and mouse interactions. The plugin exposes several of the most common events. For each of these events, the event is emitted in the Angular Zone, so you shouldn't have to do anything extra to get change detection to work. For a working example, check out the events section of the demo.

Mouse Interactions: LeafletMouseEvent

The following events are provided:

Map Zoom and Move: LeafletEvent

The following events are provided:

Getting a Reference to the Map

Occasionally, you may need to directly access the Leaflet map instance. For example, to call invalidateSize() when the map div changes size or is shown/hidden. There are a couple of different ways to achieve this depending on what you're trying to do.

The easiest and most flexible way is to use the output binding leafletMapReady. This output is invoked after the map is created, the argument of the event being the Map instance.

The second is to get a reference to the leaflet directive itself - and there are a couple of ways to do this. With a reference to the directive, you can invoke the getMap() function to get a reference to the Map instance.

(leafletMapReady): Map

This output is emitted when once when the map is initially created inside of the Leaflet directive. The event will only fire when the map exists and is ready for manipulation.

<div leaflet
     [leafletOptions]="options"
     (leafletMapReady)="onMapReady($event)">
</div>
onMapReady(map: Map) {
    // Do stuff with map
}

This method of getting the map makes the most sense if you are using the Leaflet directive inside your own component and just need to add some limited functionality or register some event handlers.

Inject LeafletDirective into your Component

This is the more advanced technique and it won't always work depending on your setup. In particular, this will likely not work unless you are writing your own third-party library that extends the functionality of ngx-leaflet. If this approach does not work for you, try using the leafletMapReady event described above.

In Angular.io, directives are injectable the same way that Services are. This means that you can create your own component or directive and inject the LeafletDirective into it. This will only work if your custom component/directive exists on the same DOM element and is ordered after the injected LeafletDirective, or if it is on a child DOM element.

<!-- On the same DOM element -->
<div leaflet myCustomDirective>
</div>

<!-- On a child DOM element -->
<div leaflet>
    <div myCustomDirective></div>
</div>
@Directive({
    selector: '[myCustomDirective]'
})
export class MyCustomDirective {
    leafletDirective: LeafletDirective;

    constructor(leafletDirective: LeafletDirective) {
        this.leafletDirective = leafletDirective;
    }

    someFunction() {
        if (null != this.leafletDirective.getMap()) {
            // Do stuff with the map
        }
    }
}

The benefit of this approach is it's a bit cleaner if you're interested in adding some reusable capability to the existing leaflet map directive. As mentioned above, it might not work depending on how you are packaging your component. This is how the @bluehalo/ngx-leaflet-draw and @bluehalo/ngx-leaflet-d3 packages work, so you can use them as references.

A Note About Change Detection

Change detection is at the core of how Angular works. Angular.io uses Zone.js to scope how and when (events, actions, etc.) to trigger change detection. It's important to scope it carefully because change detection can be fairly expensive, so you don't want it to happen constantly.

Libraries like ngx-leaflet have to decide what to do inside and outside of the Angular zone, balancing convenience and performance. Leaflet registers handlers for a lot of mouse events. To mitigate the performance impact of constantly running change detection on all mouse events (including mousemove), ngx-leaflet runs most of the Leaflet code outside of the Angular zone. The impact of this is that Angular won't automatically detect changes that you make inside of a Leaflet event callback.

The solution is to either make sure that Angular relevant changes are made inside of Angular's zone or to manually tell Angular to detect changes.

Running Inside of Angular's Zone

Leaflet event handlers run outside of Angular's zone, where changes to input bound fields will not be detected automatically. To ensure your changes are detected and applied, you need to make those changed inside of Angular's zone. Fortunately, this is extremely easy.

fitBounds: any = null;
circle = circle([ 46.95, -122 ], { radius: 5000 });

// Inject the Change Detector into your component
constructor(private zone: NgZone) {}

ngOnInit() {

    // The 'add' event callback handler happens outside of the Angular zone
    this.circle.on('add', () => {

        // But, we can run stuff inside of Angular's zone by calling NgZone.run()
        // everything inside the arrow function body happens inside of Angular's zone, where changes will be detected
        this.zone.run(() => {
            this.fitBounds = this.circle.getBounds();
        });

    });
}

Manually Triggering Change Detection

Another option is to manually tell the change detector to detect changes. The drawback to this option is that it is less precise. This will trigger change detection for this component and all of its children.

fitBounds: any = null;
circle = circle([ 46.95, -122 ], { radius: 5000 });

// Inject the Change Detector into your component
constructor(private changeDetector: ChangeDetectorRef) {}

ngOnInit() {

    // The 'add' event callback happens outside of the Angular zone
    this.circle.on('add', () => {

        // Because we're outside of Angular's zone, this change won't be detected
        this.fitBounds = this.circle.getBounds();

        // But, it will if we tell Angular to detect changes 
        this.changeDetector.detectChanges();

    });
}

A Note About Markers

If you use this component in an Angular.io project and your project uses a bundler like Webpack, you might run into issues using Markers on maps. The issue is related to how Leaflet manipulates the image URLs used to render markers when you are using the default marker images. The url manipulation is done at runtime and it alters the URLs in a way that breaks their format (this happens regardless of if you're using a file-loader or a url-loader). The demo contained in this project demonstrates how to get around this problem (at least in a Webpack environment). But, here is a rough overview of the steps taken to get them working.

Webpack Marker Workaround

  1. Import the marker images in your vendor file to get Webpack to process the images in the asset pipeline

    import 'leaflet/dist/images/marker-shadow.png';
import 'leaflet/dist/images/marker-icon.png';

  2. Either host the images statically or use the file-loader Webpack plugin to generate the images.

  3. Determine the correct URL for the marker and marker-shadow images. If you're using a file hasher, you should be able to check Webpack's output for the generated images. If you are serving them directly without chunk hashing just figure out how to resolve the images on your server.

  4. Configure Leaflet to use the correct URLs as customer marker images

    let layer = marker([ 46.879966, -121.726909 ], {
    icon: icon({
        ...Icon.Default.prototype.options,
        iconUrl: '2b3e1faf89f94a4835397e7a43b4f77d.png',
        iconRetinaUrl: '680f69f3c2e6b90c1812a813edf67fd7.png',
        shadowUrl: 'a0c6cc1401c107b501efee6477816891.png'
    })
});

Angular CLI Marker Workaround

If you build your project using the Angular CLI, you can make the default leaflet marker assets available by doing the following:

  1. Configure the CLI (by editing angular.json)to include leaflet assets as below. Detailed instructions can be found in the asset-configuration documentation. 

    {
    ...
    "assets": [
        "assets",
        "favicon.ico",
        {
            "glob": "**/*",
            "input": "./node_modules/leaflet/dist/images",
            "output": "assets/"
        }
    ],
    ...
}

  2. Configure Leaflet to use the correct URLs as customer marker images

    let layer = marker([ 46.879966, -121.726909 ], {
    icon: icon({
        ...Icon.Default.prototype.options,
        iconUrl: 'assets/marker-icon.png',
        iconRetinaUrl: 'assets/marker-icon-2x.png',
        shadowUrl: 'assets/marker-shadow.png'
    })
});

Extensions

There are several libraries that extend the core functionality of ngx-leaflet:

Getting Help

Here's a list of articles, tutorials, guides, and help resources:

Contribute

PRs accepted. If you are part of BlueHalo, please make contributions on feature branches off of the develop branch. If you are outside of BlueHalo, please fork our repo to make contributions.

License

See LICENSE in repository for details.

Credits

Leaflet Is an awesome mapping package.