BaseDynamicLayer

Class: esri/layers/BaseDynamicLayer
Inheritance: BaseDynamicLayer Layer Accessor
Since: ArcGIS API for JavaScript 4.4

This class may be extended to create dynamic map layers. Dynamic layers display an image dynamically generated on the server based on a request, including the extent and size of the image. The exported image covers the entire view extent. Each interaction on the view (e.g. panning, zooming) will result in an export of a new image on the server. Each export is unique so it cannot be cached in the browser.

You can create a custom DynamicLayer by calling its createSubclass() method. You may create a custom dynamic layer for one of the following reasons:

  • The source of the images isn't explicitly supported by the ArcGIS API for JavaScript
  • Images need to be preprocessed prior to display in the view

Request images as they are defined

To request images as they are predefined from a data source, overwrite the getTileUrl() method so it returns the URL for the requested tile for a given level, row and column.

var MyCustomDynamicLayer = BaseDynamicLayer.createSubclass({
 // properties of the custom dynamic layer
 properties: {
   getMapUrl: null,
   getMapParameters: null
 },

 // override getImageUrl() to generate URL to the image
 getImageUrl: function (extent, width, height) {
   // generate the URL for the map image
   var urlVariables = this._prepareQuery(this.getMapParameters, extent, width, height);
   var queryString = this._joinUrlVariables(urlVariables);

   // return the URL to the generated image
   return this.getMapUrl + "?" + queryString;
 },
 ...
});

See the Custom DynamicLayer sample for an example of this workflow.

Preprocess images prior to display

If data needs to be preprocessed prior to display, then override the fetchImage() method to generate an html image element or canvas element by processing the data returned by the server. For example, if you need to apply a compositing operation to the image returned from the server before the image is displayed then you would override this method.

// Fetches images for given extent and size
fetchImage: function (extent, width, height){
  var url = this.getImageUrl(extent, width, height);

  // request for the image  based on the generated url
  return esriRequest(url, {
    responseType: "image",
    allowImageDataAccess: true
  })
  .then(function(response) {
    var image = response.data;

    // create a canvas with teal fill
    var canvas = document.createElement("canvas");
    var context = canvas.getContext("2d");
    canvas.width = width;
    canvas.height = height;

    // Apply destination-atop operation to the image returned from the server
    context.fillStyle = "rgb(0,200,200)";
    context.fillRect(0, 0, width, height);
    context.globalCompositeOperation = "destination-atop";
    context.drawImage(image, 0, 0, width, height);

    return canvas;
  }.bind(this));
}

The layer is responsible for generating the image URL and fetching the image from the server for the extent and size provided by the LayerView. The LayerView displays the fetched tiles.

If the custom dynamic layer requires loadable resources, then you must load all loadable dependencies on the layer, within the load() method. Add the promise returned from the loadable resource with the addResolvingPromise() method. The layer will then wait for all of dependencies to finish loading before it is considered loaded.

Known Limitations

There is no support for custom dynamic layers in 3D at 4.4.

See also:

Property Overview

Any properties can be set, retrieved or listened to. See the Working with Properties topic.
NameTypeSummaryClass
String

The name of the class.

more details
more detailsAccessor
Extent

The full extent of the layer.

more details
more detailsLayer
String

The unique ID assigned to the layer.

more details
more detailsLayer
String

Indicates how the layer should display in the LayerList widget.

more details
more detailsLayer
Boolean

Indicates whether the layer's resources have loaded.

more details
more detailsLayer
Error

The Error object returned if an error occurred while loading.

more details
more detailsLayer
String

Represents the status of a load operation.

more details
more detailsLayer
Object[]

A list of warnings which occurred while loading.

more details
more detailsLayer
Number

The maximum scale at which the layer is visible in the view.

more details
more detailsBaseDynamicLayer
Number

The minimum scale at which the layer is visible in the view.

more details
more detailsBaseDynamicLayer
Number

The opacity of the layer.

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more detailsLayer
String

The title of the layer used to identify it in places such as the Legend and LayerList widgets.

more details
more detailsLayer
String

The layer type.

more details
more detailsBaseDynamicLayer
Boolean

Indicates if the layer is visible in the View.

more details
more detailsLayer

Property Details

declaredClassStringreadonly inherited

The name of the class. The declared class name is formatted as esri.folder.className.

The full extent of the layer. By default, this is worldwide. This property may be used to set the extent of the view to match a layer's extent so that its features appear to fill the view. See the sample snippet below.

Example:
// Once the layer loads, set the view's extent to the layer's fullextent
layer.then(function(){
  view.extent = layer.fullExtent;
});

The unique ID assigned to the layer. If not set by the developer, it is automatically generated when the layer is loaded.

Indicates how the layer should display in the LayerList widget. The known values are listed below.

ValueDescription
showThe layer is visible in the table of contents.
hideThe layer is hidden in the table of contents.
hide-childrenIf the layer is a GroupLayer, hide the children layers from the table of contents.
Default Value: show

loadedBooleanreadonly inherited

Indicates whether the layer's resources have loaded. When true, all the properties of the object can be accessed.

Default Value: false

loadErrorErrorreadonly inherited

The Error object returned if an error occurred while loading.

Default Value: null

loadStatusStringreadonly inherited

Represents the status of a load operation.

ValueDescription
not-loadedThe object's resources have not loaded.
loadingThe object's resources are currently loading.
loadedThe object's resources have loaded without errors.
failedThe object's resources failed to load. See loadError for more details.
Default Value: not-loaded

loadWarningsObject[]readonly inherited

A list of warnings which occurred while loading.

maxScaleNumber

The maximum scale at which the layer is visible in the view. If the map is zoomed in beyond this scale, the layer will not be visible. A value of 0 means the layer does not have a maximum scale.

Default Value: 0
Examples:
// The layer will not be visible when the view is zoomed beyond a scale of 1:1,000
layer.maxScale = 1000;
// The layer's visibility is not restricted to a maximum scale.
layer.maxScale = 0;

minScaleNumber

The minimum scale at which the layer is visible in the view. If the map is zoomed out beyond this scale, the layer will not be visible. A value of 0 means the layer does not have a minimum scale.

Default Value: 0
Examples:
// The layer will not be visible when the view is zoomed beyond a scale of 1:3,000,000
layer.minScale = 3000000;
// The layer's visibility is not restricted to a minimum scale.
layer.minScale = 0;

The opacity of the layer. This value can range between 1 and 0, where 0 is 100 percent transparent and 1 is completely opaque.

Default Value: 1
Example:
// Makes the layer 50% transparent
layer.opacity = 0.5;

The title of the layer used to identify it in places such as the Legend and LayerList widgets.

typeStringreadonly

The layer type. For BaseDynamicLayer the type is always base-dynamic.

Indicates if the layer is visible in the View. When false, the layer may still be added to a Map instance that is referenced in a view, but its features will not be visible in the view.

Default Value: true
Example:
// The layer is no longer visible in the view
layer.visible = false;

Method Overview

NameReturn TypeSummaryClass
Promise

Adds a promise to the layer's loadable chain.

more details
more detailsBaseDynamicLayer
Promise

An instance of this class is a Promise.

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more detailsLayer

Cancels a load() operation if it is already in progress.

more details
more detailsLayer

Emits an event on the instance.

more details
more detailsLayer
Promise<Object>

Fetches custom attribution data for the layer when it becomes available.

more details
more detailsLayer
Promise<(HTMLImageElement|HTMLCanvasElement)>

This method fetches the image for the specified extent and size.

more details
more detailsBaseDynamicLayer
Promise<String>| String

This method returns a URL to an image for a given extent, width, and height.

more details
more detailsBaseDynamicLayer
Boolean

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

more details
more detailsLayer
Boolean

An instance of this class is a Promise.

more details
more detailsLayer
Boolean

An instance of this class is a Promise.

more details
more detailsLayer
Boolean

An instance of this class is a Promise.

more details
more detailsLayer
Promise

Loads the resources referenced by this class.

more details
more detailsLayer
Object

Registers an event handler on the instance.

more details
more detailsLayer
Promise

An instance of this class is a Promise.

more details
more detailsLayer
Promise

An instance of this class is a Promise.

more details
more detailsLayer

Method Details

addResolvingPromise(promiseToLoad){Promise}

Adds a promise to the layer's loadable chain. This is typically used in the load() method to ensure that all loadable resources required for the layer to function are loaded prior to this layer resolving and becoming loaded.

Parameter:
promiseToLoad Promise

A promise that must resolve for the layer to resolve and move from the loading status to being loaded.

Returns:
TypeDescription
PromiseResolves when the given promise resolves.
Example:
// the externalLayer must load() prior to the MyDynamicLayer
// resolving and moving to the "loaded" status
var MyDynamicLayer = BaseElevationLayer.createSubclass({
  load: function() {
    var promise = this.requiredLayer.load();
    this.addResolvingPromise(promise);
  }
});

always(callbackOrErrback){Promise}inherited

An instance of this class is a Promise. Therefore always() may be used to execute a function if the promise is rejected or resolved. The input function will always execute no matter the response. For more information about promises, see the Working with Promises guide page.

Parameter:
callbackOrErrback Function
optional

The function to execute when the promise is rejected or resolved.

Returns:
TypeDescription
PromiseReturns a new promise for the result of callbackOrErrback.
Example:
// Although this example uses MapView, any class instance that is a promise may use always() in the same way
var view = new MapView();
view.always(function(){
  // This function will always execute whether or not the promise is resolved or rejected
});

cancelLoad()inherited

Cancels a load() operation if it is already in progress.

emit(type, event)protectedinherited

Since: ArcGIS API for JavaScript 4.5

Emits an event on the instance. This method should only be used when creating subclasses that inherit from Evented.

Parameters:
type String

The name of the event.

event Object

The event payload.

fetchAttributionData(){Promise<Object>}inherited

Fetches custom attribution data for the layer when it becomes available.

Returns:
TypeDescription
Promise< Object>Resolves to an object containing custom attribution data for the layer.

fetchImage(extent, width, height, options){Promise<(HTMLImageElement|HTMLCanvasElement)>}

This method fetches the image for the specified extent and size. Override this method if the data returned from the server needs to be processed before it can be displayed. For example, if the server returns binary data, override this method to convert the binary data to an image.

Parameters:
extent Extent

The extent of the view. This value is provided by the LayerView.

width Number

The width of the view in pixels. This value is provided by the LayerView.

height Number

The height of the view in pixels. This value is provided by the LayerView.

options Object
optional

Optional settings for the image request. The options have the following properties.

Specification:
allowImageDataAccess Boolean
optional

Indicates if access to pixels of the image is allowed. This value must be set to true if the layer will be drawn in 3D and WebGL textures are required to display the layer. Loading of WebGL textures is dependent on cross-domain access controls. This option allows cross-domain access to create WebGL textures.

Returns:
TypeDescription
Promise<( HTMLImageElement| HTMLCanvasElement)>Returns a promise that resolves to an HTMLImageElement or HTMLCanvasElement.
Example:
// Fetches images for given extent and size
fetchImage: function (extent, width, height){
  var url = this.getImageUrl(extent, width, height);

  // request for the image  based on the generated url
  return esriRequest(url, {
    responseType: "image",
    allowImageDataAccess: true
  })
  .then(function(response) {
    var image = response.data;

    var canvas = document.createElement("canvas");
    var context = canvas.getContext("2d");
    canvas.width = width;
    canvas.height = height;

    // Apply destination-atop operation to the image returned from the server
    context.fillStyle = "rgb(0,200,200)";
    context.fillRect(0, 0, width, height);
    context.globalCompositeOperation = "destination-atop";
    context.drawImage(image, 0, 0, width, height);

    return canvas;
  }.bind(this));
}

getImageUrl(extent, width, height){Promise<String>| String}

This method returns a URL to an image for a given extent, width, and height. Override this method to construct the URL for the image based on user interaction.

Parameters:
extent Extent

Extent of the view. This value is populated by the LayerView.

width Number

Width of the view in pixels. This value is populated by the LayerView.

height Number

Height of the view in pixels. This value is populated by the LayerView.

Returns:
TypeDescription
Promise< String> | StringReturns a string or a promise that resolves to a string. The string is the URL to the image.
See also:

hasEventListener(type){Boolean}inherited

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

Parameter:
type String

The name of the event.

Returns:
TypeDescription
BooleanReturns true if the class supports the input event.

isFulfilled(){Boolean}inherited

An instance of this class is a Promise. Therefore isFulfilled() may be used to verify if the promise is fulfilled (either resolved or rejected). If it is fulfilled, true will be returned. See the Working with Promises guide page for more information about promises.

Returns:
TypeDescription
BooleanIndicates whether the promise has been fulfilled (either resolved or rejected).

isRejected(){Boolean}inherited

An instance of this class is a Promise. Therefore isRejected() may be used to verify if the promise is rejected. If it is rejected, true will be returned. See the Working with Promises guide page for more information about promises.

Returns:
TypeDescription
BooleanIndicates whether the promise has been rejected.

isResolved(){Boolean}inherited

An instance of this class is a Promise. Therefore isResolved() may be used to verify if the promise is resolved. If it is resolved, true will be returned. See the Working with Promises guide page for more information about promises.

Returns:
TypeDescription
BooleanIndicates whether the promise has been resolved.

Loads the resources referenced by this class. This method automatically executes for a View and all of the resources it references in Map if the view is constructed with a map instance.

This method must be called by the developer when accessing a resource that will not be loaded in a View.

Returns:
TypeDescription
PromiseResolves when the resources have loaded.

on(type, listener){Object}inherited

Registers an event handler on the instance. Call this method to hook an event with a listener. See the Events summary table for a list of listened events.

Parameters:
type String

The name of event to listen for.

listener Function

The function to call when the event is fired.

Returns:
TypeDescription
ObjectReturns an event handler with a remove() method that can be called to stop listening for the event.
PropertyTypeDescription
removeFunctionWhen called, removes the listener from the event.
See also:
Example:
view.on("click", function(event){
  // event is the event handle returned after the event fires.
  console.log(event.mapPoint);
});

otherwise(errback){Promise}inherited

An instance of this class is a Promise. Use otherwise() to call a function once the promise is rejected.

Parameter:
errback Function
optional

The function to execute when the promise fails.

Returns:
TypeDescription
PromiseReturns a new promise for the result of errback.
Example:
// Although this example uses MapView, any class instance that is a promise may use otherwise() in the same way
var view = new MapView();
view.otherwise(function(error){
  // This function will execute if the promise is rejected due to an error
});

then(callback, errback, progback){Promise}inherited

An instance of this class is a Promise. Therefore then() 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 promise resolves (when the instance of the class loads). The errback executes if the promise fails. See the Working with Promises guide page for additional details.

Parameters:
callback Function
optional

The function to call when the promise resolves.

errback Function
optional

The function to execute when the promise fails.

progback Function
optional

The function to invoke when the promise emits a progress update.

Returns:
TypeDescription
PromiseReturns a new promise for the result of callback that may be used to chain additional functions.
Example:
// Although this example uses MapView, any class instance that is a promise may use then() in the same way
var view = new MapView();
view.then(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
});

Event Overview

NameTypeSummaryClass
{view: View,layerView: LayerView}

Fires after the layer's LayerView is created and rendered in a view.

more details
more detailsLayer
{view: View,layerView: LayerView}

Fires after the layer's LayerView is destroyed and no longer renders in a view.

more details
more detailsLayer

Event Details

layerview-createinherited

Fires after the layer's LayerView is created and rendered in a view.

Properties:
view View

The view in which the layerView was created.

layerView LayerView

The LayerView rendered in the view representing the layer in layer.

See also:
Example:
// This function will fire each time a layer view is created for this
// particular view.
layer.on("layerview-create", function(event){
  // The LayerView for the layer that emitted this event
  event.layerView;
});

layerview-destroyinherited

Fires after the layer's LayerView is destroyed and no longer renders in a view.

Properties:
view View

The view in which the layerView was destroyed.

layerView LayerView

The destroyed LayerView representing the layer.

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