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;
 },
 ...
});

// 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));
}

Property Overview

Property Details

declaredClassStringreadonly

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

fullExtentExtent autocast

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;
});

idString

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

listModeString

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

Value	Description
show	The layer is visible in the table of contents.
hide	The layer is hidden in the table of contents.
hide-children	If the layer is a GroupLayer, hide the children layers from the table of contents.

Default Value: show

loadedBooleanreadonly

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

Default Value: false

loadErrorErrorreadonly

The Error object returned if an error occurred while loading.

Default Value: null

loadStatusStringreadonly

Represents the status of a load operation.

Value	Description
not-loaded	The object's resources have not loaded.
loading	The object's resources are currently loading.
loaded	The object's resources have loaded without errors.
failed	The object's resources failed to load. See loadError for more details.

Default Value: not-loaded

loadWarningsObject[]readonly

A list of warnings which occurred while loading.

opacityNumber

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;

titleString

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.

visibleBoolean

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

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:

Type	Description
Promise	Resolves 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:

Type	Description
Promise	Returns 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.

fetchAttributionData(){Promise}inherited

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

Returns:

Type	Description
Promise	Resolves to an object containing custom attribution data for the layer.

fetchImage(extent, width, height, options){Promise}

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:

Type	Description
Promise	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}

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:

Type	Description
Promise | String	Returns a string or a promise that resolves to a string. The string is the URL to the image.

See also:

• Custom dynamic layer sample

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:

Type	Description
Boolean	Returns 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:

Type	Description
Boolean	Indicates 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:

Type	Description
Boolean	Indicates 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:

Type	Description
Boolean	Indicates whether the promise has been resolved.

load(){Promise}inherited

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:

Type	Description
Promise	Resolves 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:

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

See also:

• dojo/on

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:

Type	Description
Promise	Returns 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:

Type	Description
Promise	Returns 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

{view: View,layerView: LayerView}

{view: View,layerView: LayerView}

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:

• View.whenLayerView()

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.