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Showing content from https://developers.arcgis.com/javascript/latest/api-reference/esri-widgets-Legend.html below:

Legend | API Reference | ArcGIS Maps SDK for JavaScript 4.33

ESM: import Legend from "@arcgis/core/widgets/Legend.js";

CDN: const Legend = await $arcgis.import("@arcgis/core/widgets/Legend.js");

Class: @arcgis/core/widgets/Legend

Since: ArcGIS Maps SDK for JavaScript 4.0

The Legend widget describes the symbols used to represent layers in a map. All symbols and text used in this widget are configured in the Renderer of the layer. The legend will only display layers and sublayers that are visible in the view unless respectLayerVisibility is false.

The legend automatically updates when

the visibility of a layer or sublayer changes
a layer is added or removed from the map
a layer's renderer, opacity, or title is changed
the legendEnabled property is changed (set to true or false on the layer)

You can use the view's DefaultUI to add widgets to the view's user interface via the ui property on the view.

Expand the "Read more" section below to view various examples of legends based on renderer type.

Unique values

Continuous color

Classed color

Continuous size

Size - above and below

Dot density

Predominance

Relationship

See also

Example

let legend = new Legend({
  view: view
});

view.ui.add(legend, "bottom-right");

Constructors

Legend Constructor new Legend(properties)

Parameter

optional

See the properties for a list of all the properties that may be passed into the constructor.

Example

// typical usage
let legend = new Legend({
  view: view
});

Property Overview Any properties can be set, retrieved or listened to. See the Watch for changes topic.

Show inherited properties Hide inherited properties

Property Details

: Collection of ActiveLayerInfo objects used by the legend view to display data in the legend. The legend widget watches this property to hide or display the layer's legend when an ActiveLayerInfo is removed from or added to this collection.

basemapLegendVisible Property basemapLegendVisible Boolean

Indicates whether to show the Basemap layers in the Legend. If you set this property to true and specify layerInfos, the basemap layers you want included in the legend must also be specified in layerInfos.

Example

legend.basemapLegendVisible = true;

The ID or node representing the DOM element containing the widget. This property can only be set once. The following examples are all valid use case when working with widgets.

Examples

// Create the HTML div element programmatically at runtime and set to the widget's container
const basemapGallery = new BasemapGallery({
  view: view,
  container: document.createElement("div")
});

// Add the widget to the top-right corner of the view
view.ui.add(basemapGallery, {
  position: "top-right"
});

// Specify an already-defined HTML div element in the widget's container

const basemapGallery = new BasemapGallery({
  view: view,
  container: basemapGalleryDiv
});

// Add the widget to the top-right corner of the view
view.ui.add(basemapGallery, {
  position: "top-right"
});

// HTML markup
<body>
  <div id="viewDiv"></div>
  <div id="basemapGalleryDiv"></div>
</body>

// Specify the widget while adding to the view's UI
const basemapGallery = new BasemapGallery({
  view: view
});

// Add the widget to the top-right corner of the view
view.ui.add(basemapGallery, {
  position: "top-right"
});

declaredClass Inherited Property declaredClass Stringreadonly Since: ArcGIS Maps SDK for JavaScript 4.7 Accessor since 4.0, declaredClass added at 4.7.: The name of the class. The declared class name is formatted as esri.folder.className.

headingLevel Property headingLevel Number Since: ArcGIS Maps SDK for JavaScript 4.20 Legend since 4.0, headingLevel added at 4.20.

Indicates the heading level to use for the legend title. By default, legend titles are rendered as level 3 headings (e.g. <h3>Legend title</h3>). Depending on the legend placement in your app, you may need to adjust this heading for proper semantics. This is important for meeting accessibility standards.

Example

// legend title will render as an <h2>
legend.headingLevel = 2;

hideLayersNotInCurrentView Property hideLayersNotInCurrentView Boolean Since: ArcGIS Maps SDK for JavaScript 4.21 Legend since 4.0, hideLayersNotInCurrentView added at 4.21.

When true, layers will only be shown in the legend if they are visible in the view's extent. When data from a layer is not visible in the view, the layer's legend information will be hidden. Only layers that implement the createQuery() and queryFeatureCount() methods are supported by hideLayersNotInCurrentView.

To hide layers completely from the legend, you should set the legendEnabled property of the layer to false.

Example

// layers not displayed in the view
// will not be shown in the legend
legend.hideLayersNotInCurrentView = true;

Since: ArcGIS Maps SDK for JavaScript 4.27 Legend since 4.0, icon added at 4.27.: Icon which represents the widget. It is typically used when the widget is controlled by another one (e.g. in the Expand widget).

id Inherited Property id String: The unique ID assigned to the widget when the widget is created. If not set by the developer, it will default to the container ID, or if that is not present then it will be automatically generated.

Since: ArcGIS Maps SDK for JavaScript 4.7 Legend since 4.0, label added at 4.7.: The widget's default label.

Specifies a subset of the layers to display in the legend. This includes any basemap layers you want to be visible in the legend. If this property is not set, all layers in the map will display in the legend, including basemap layers if basemapLegendVisible is true. Objects in this array are defined with the properties listed below.

Properties

optional

Specifies a title for the layer to display above its symbols and descriptions. If no title is specified the service name is used.

A layer to display in the legend.

optional

Only applicable if the layer is a MapImageLayer, SubtypeGroupLayer or WMSLayer. The IDs of the sublayers for which to display legend information. Since version 4.23.

Example

const subtypeGroupLayer = webmap.layers.getItemAt(0);
const subtypeSubLayer = subtypeGroupLayer.sublayers.getItemAt(1);
const subtypeSublayerId = parseInt(subtypeSubLayer.subtypeCode);
const legend = new Legend({
  view: view,
  layerInfos: [
    {
      layer: subtypeGroupLayer,
      sublayerIds: [subtypeSublayerId]
    }
  ]
});

respectLayerDefinitionExpression Property respectLayerDefinitionExpression Boolean Since: ArcGIS Maps SDK for JavaScript 4.30 Legend since 4.0, respectLayerDefinitionExpression added at 4.30.: If a layer uses a unique value render, only features that satisfy the layer's definition expression will be displayed in the legend when set to true.

respectLayerVisibility Property respectLayerVisibility Boolean Since: ArcGIS Maps SDK for JavaScript 4.13 Legend since 4.0, respectLayerVisibility added at 4.13.

Determines whether to respect the properties of the layers in the map that control the legend's visibility (minScale, maxScale, legendEnabled). By default, a layer's legend elements will not render in the legend given the following conditions:

The layer's legendEnabled property is set to false.
If the view's scale is outside the visibility range defined by the layer's minScale and maxScale properties.

When the respectLayerVisibility property of the legend is set to false, the legend elements for each layer in the map will always display, thus disregarding the minScale, maxScale, and legendEnabled properties for each layer in the map.

Example

// Always displays legend elements for the map's layers
// regardless of their minScale, maxScale, and legendEnabled properties
legend.respectLayerVisibility = false;

Since: ArcGIS Maps SDK for JavaScript 4.7 Legend since 4.0, style added at 4.7.

Indicates the style of the legend. The style determines the legend's layout and behavior. You can either specify a string or an object to indicate the style. The known string values are the same values listed in the table within the type property.

Properties

type String

Specifies the style of the legend. There are two possible values listed in the table below:

Value Description classic The legend has a portrait orientation. The user can scroll vertically when many elements are included in the legend's content. card In wide views, the legend has a landscape orientation that allows users to scroll horizontally to view all legend elements. This style can be responsive, making it ideal for mobile web apps. In smaller views, the legend collapses to occupy less space. One element is shown at a time in a card-style layout, which the user can navigate horizontally.

Possible Values:"classic"|"card"

layout String optional

Default Value:stack

When a card type is specified, you can specify one of the following layout options.

Value Description auto This layout is responsive so that in wide views the legend has a side-by-side layout, and a stack layout in smaller (mobile) views. side-by-side The legend has a landscape orientation that allows users to scroll horizontally to view multiple legend cards at a time. stack The legend cards are stacked, which conserves space, but restricts the user to seeing only one card at a time.

Possible Values:"auto"|"side-by-side"|"stack"

Default Value:"classic"

Examples

// renders the legend in the card style with a "stack" layout
legend.style = "card";

// renders the legend in the card style with a responsive
// layout that toggles between "stack" and "side-by-side"
legend.style = {
  type: "card",
  layout: "auto"
};

// renders the legend in the classic layout
legend.style = "classic";

: The view model for this widget. This is a class that contains all the logic (properties and methods) that controls this widget's behavior. See the LegendViewModel class to access all properties and methods on the widget.

visible Inherited Property visible Boolean

Indicates whether the widget is visible.

If false, the widget will no longer be rendered in the web document. This may affect the layout of other elements or widgets in the document. For example, if this widget is the first of three widgets associated to the upper right hand corner of the view UI, then the other widgets will reposition when this widget is made invisible. For more information, refer to the css display value of "none".

Example

// Hides the widget in the view
widget.visible = false;

Method Overview

Show inherited methods Hide inherited methods

Method Details

addHandles Inherited Method addHandles(handleOrHandles, groupKey) Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, addHandles added at 4.25.

Adds one or more handles which are to be tied to the lifecycle of the object. The handles will be removed when the object is destroyed.

// Manually manage handles
const handle = reactiveUtils.when(
  () => !view.updating,
  () => {
    wkidSelect.disabled = false;
  },
  { once: true }
);

this.addHandles(handle);

// Destroy the object
this.destroy();

Parameters

Handles marked for removal once the object is destroyed.

groupKey *

optional

Key identifying the group to which the handles should be added. All the handles in the group can later be removed with Accessor.removeHandles(). If no key is provided the handles are added to a default group.

classes Inherited Method classes(classNames){String} Since: ArcGIS Maps SDK for JavaScript 4.7 Widget since 4.2, classes added at 4.7.

A utility method used for building the value for a widget's class property. This aids in simplifying css class setup.

Returns

Type Description String The computed class name.

Example

// .tsx syntax showing how to set css classes while rendering the widget

render() {
  const dynamicClasses = {
    [css.flip]: this.flip,
    [css.primary]: this.primary
  };

  return (
    <div class={classes(css.root, css.mixin, dynamicClasses)} />
  );
}

destroy Inherited Method destroy(): Destroys the widget instance.

emit Inherited Method emit(type, event){Boolean} Since: ArcGIS Maps SDK for JavaScript 4.5 Widget since 4.2, emit added at 4.5.

Emits an event on the instance. This method should only be used when creating subclasses of this class.

Parameters

The name of the event.

optional

The event payload.

Returns

Type Description Boolean true if a listener was notified

hasEventListener Inherited Method hasEventListener(type){Boolean}

Indicates whether there is an event listener on the instance that matches the provided event name.

Returns

Type Description Boolean Returns true if the class supports the input event.

hasHandles Inherited Method hasHandles(groupKey){Boolean} Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, hasHandles added at 4.25.

Returns true if a named group of handles exist.

Parameter

groupKey *

optional

A group key.

Returns

Type Description Boolean Returns true if a named group of handles exist.

Example

// Remove a named group of handles if they exist.
if (obj.hasHandles("watch-view-updates")) {
  obj.removeHandles("watch-view-updates");
}

isFulfilled Inherited Method isFulfilled(){Boolean} Since: ArcGIS Maps SDK for JavaScript 4.19 Widget since 4.2, isFulfilled added at 4.19.

isFulfilled() may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected). If it is fulfilled, true will be returned.

Returns

Type Description Boolean Indicates whether creating an instance of the class has been fulfilled (either resolved or rejected).

isRejected Inherited Method isRejected(){Boolean} Since: ArcGIS Maps SDK for JavaScript 4.19 Widget since 4.2, isRejected added at 4.19.

isRejected() may be used to verify if creating an instance of the class is rejected. If it is rejected, true will be returned.

Returns

Type Description Boolean Indicates whether creating an instance of the class has been rejected.

isResolved Inherited Method isResolved(){Boolean} Since: ArcGIS Maps SDK for JavaScript 4.19 Widget since 4.2, isResolved added at 4.19.

isResolved() may be used to verify if creating an instance of the class is resolved. If it is resolved, true will be returned.

Returns

Type Description Boolean Indicates whether creating an instance of the class has been resolved.

on Inherited Method on(type, listener){Object}

Registers an event handler on the instance. Call this method to hook an event with a listener.

Returns

Type Description Object Returns an event handler with a remove() method that should be called to stop listening for the event(s). Property Type Description remove Function When called, removes the listener from the event.

Example

view.on("click", function(event){
  // event is the event handle returned after the event fires.
  console.log(event.mapPoint);
});

postInitialize Inherited Method postInitialize(): Executes after widget is ready for rendering.

removeHandles Inherited Method removeHandles(groupKey) Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, removeHandles added at 4.25.

Removes a group of handles owned by the object.

Parameter

groupKey *

optional

A group key or an array or collection of group keys to remove.

Example

obj.removeHandles(); // removes handles from default group

obj.removeHandles("handle-group");
obj.removeHandles("other-handle-group");

render Inherited Method render(){Object}

This method is implemented by subclasses for rendering.

Returns

Type Description Object The rendered virtual node.

renderNow Inherited Method renderNow(): Renders widget to the DOM immediately.

scheduleRender Inherited Method scheduleRender(): Schedules widget rendering. This method is useful for changes affecting the UI.

when Inherited Method when(callback, errback){Promise} Since: ArcGIS Maps SDK for JavaScript 4.19 Widget since 4.2, when added at 4.19.

when() may be leveraged once an instance of the class is created. This method takes two input parameters: a callback function and an errback function. The callback executes when the instance of the class loads. The errback executes if the instance of the class fails to load.

Parameters

optional

The function to call when the promise resolves.

optional

The function to execute when the promise fails.

Returns

Type Description Promise Returns a new Promise for the result of callback.

Example

// Although this example uses the BasemapGallery widget, any class instance that is a promise may use when() in the same way
let bmGallery = new BasemapGallery();
bmGallery.when(function(){
  // This function will execute once the promise is resolved
}, function(error){
  // This function will execute if the promise is rejected due to an error
});

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