BaseLayerView2D | API Reference | ArcGIS Maps SDK for JavaScript 4.32

Represents the LayerView of a Layer after it has been added to a Map with a MapView.

This class may be extended to create a custom LayerView for a Layer. A LayerView is created on demand by the MapView when a layer is added the to list of layers of its map.

The subclass can implement multiple functions of the LayerView lifecycle. First, the attach() method is called when the LayerView is about to start drawing the layer's content. Then during the life of the LayerView, the render() method is called during the MapView rendering phase. The render() method has access to a canvas 2d context in which it can render the content available for display. Finally the detach() method is called after the layer is removed from the map. It releases all allocated resources and stops on-going requests.

Example

let TileBorderLayerView2D = BaseLayerView2D.createSubclass({
   // Example of a render implementation that draws tile boundaries
   render(renderParameters) {
     let tileSize = this.layer.tileInfo.size[0];
     let state = renderParameters.state;
     let pixelRatio = state.pixelRatio;
     let width = state.size[0];
     let height = state.size[1];
     let context = renderParameters.context;
     let coords = [0, 0];

     context.fillStyle = "rgba(0,0,0,0.25)";
     context.fillRect(0, 0, width * pixelRatio, height * pixelRatio);

     // apply rotation for everything that will be applied to the canvas
     if (state.rotation !== 0) {
       context.translate(width * pixelRatio * 0.5, height * pixelRatio * 0.5);
       context.rotate((state.rotation * Math.PI) / 180);
       context.translate(- width * pixelRatio * 0.5, -height * pixelRatio * 0.5);
     }

     // Set the style for all the text.
     context.font = "24px monospace";
     context.fillStyle = "black";
     context.shadowBlur = 1;

     for (const tile of this.tiles) {
       let screenScale = tile.resolution / state.resolution * pixelRatio;

       state.toScreenNoRotation(coords, tile.coords);

       // Draw the tile boundaries
       context.strokeRect(coords[0], coords[1], tileSize * screenScale, tileSize * screenScale);

       // Draw the tile information
       context.shadowColor = "white";
       context.fillText(
         tile.level + "/" + tile.row + "/" + tile.col + "/" + tile.world,
         coords[0] + 12,
         coords[1] + 24,
         tileSize * screenScale
       );
       context.shadowColor = "transparent";
     }
   }
 });

 let CustomTileLayer = Layer.createSubclass({
   tileInfo: TileInfo.create({ spatialReference: { wkid: 3857 }}),

   createLayerView(view) {
     if (view.type === "2d") {
       return new TileBorderLayerView2D({
         view: view,
         layer: this
       });
     }
   }
 });

Constructors

BaseLayerView2D Constructor new BaseLayerView2D(properties)

Parameter

properties Object

optional

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

Property Overview

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

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Type	Summary	Class
String	The name of the class.	Accessor
Layer	References the layer this LayerView represents.	BaseLayerView2D
Boolean	Indicates if the spatialReference of the MapView is supported by the layer view.	LayerView
Boolean	Value is `true` if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).	LayerView
Tile []	The array of Tile objects computed to cover the MapView's visible area.	BaseLayerView2D
Boolean	Indicates if the layer view is making any updates that will impact what is displayed on the map.	LayerView
MapView	References the MapView this LayerView belongs to.	BaseLayerView2D
Boolean	When `true`, the layer is visible in the view.	LayerView
Boolean	When `true`, the layer is visible in the view at the current scale.	LayerView
Boolean	When `true`, the layer is visible in the view's timeExtent.	LayerView

Property Details

declaredClass Inherited Property declaredClass Stringreadonly Inherited from Accessor

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

layer Property layer Layer

References the layer this LayerView represents.

spatialReferenceSupported Inherited Property spatialReferenceSupported Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.23 LayerView since 4.0, spatialReferenceSupported added at 4.23.

Indicates if the spatialReference of the MapView is supported by the layer view. When false layer view will be suspended.

See also

suspended

suspended Inherited Property suspended Booleanreadonly Inherited from LayerView

Value is true if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).

See also

spatialReferenceSupported

tiles Property tiles Tile[]

The array of Tile objects computed to cover the MapView's visible area. This array is updated when the view is animating or the user is interacting with it. Then if tiles have been added or removed, tilesChanged() is called.

See also

tilesChanged()

updating Inherited Property updating Booleanreadonly Inherited from LayerView

Indicates if the layer view is making any updates that will impact what is displayed on the map. For example, this value is true when renderer, definitionExpression, filter or effect is changed or if the layer view is in the process of the fetching data.

Watch dataUpdating property instead to only know when the data has been updated (e.g. to run statistics query on all feature available in the layer view).

Default Value:false

Example

// Check for the first time layerView.updating becomes false. Then query for
// features that are visible within the view associated with the layer view.
await reactiveUtils.whenOnce(() => !layerView.updating);
const query = layerView.createQuery();
query.geometry = layerView.view.extent;
const result = layerView.queryFeatures(query);

view Property view MapView

References the MapView this LayerView belongs to.

visible Inherited Property visible Boolean Inherited from LayerView

When true, the layer is visible in the view. Value of this property is inherited from the layer.visible unless the developer overrides it. The layerView.visible will take precedence over layer.visible if both properties are set.

Default Value:true

visibleAtCurrentScale Inherited Property visibleAtCurrentScale Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.30 LayerView since 4.0, visibleAtCurrentScale added at 4.30.

When true, the layer is visible in the view at the current scale. This applies to layers that have minScale and maxScale properties set.

Known Limitations

This property is not supported in 3D SceneView tiled layers.

Default Value:true

See also

visibleAtCurrentTimeExtent
suspended

visibleAtCurrentTimeExtent Inherited Property visibleAtCurrentTimeExtent Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.30 LayerView since 4.0, visibleAtCurrentTimeExtent added at 4.30.

When true, the layer is visible in the view's timeExtent. This applies to layers that have a visibilityTimeExtent.

Default Value:true

See also

visibleAtCurrentScale
suspended

Method Overview

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Return Type	Summary	Class
	Adds one or more handles which are to be tied to the lifecycle of the object.	Accessor
	Method called when after the LayerView is created and right before it's asked to draw the layer's content.	BaseLayerView2D
	Method called after the layer is removed and the LayerView is about to be removed.	BaseLayerView2D
Boolean	Returns true if a named group of handles exist.	Accessor
Promise<(ViewHit []\|null\|undefined)>	Method to implement that is responsible for providing objects hit at the specified screen coordinates.	BaseLayerView2D
Boolean	`isFulfilled()` may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected).	LayerView
Boolean	`isRejected()` may be used to verify if creating an instance of the class is rejected.	LayerView
Boolean	`isResolved()` may be used to verify if creating an instance of the class is resolved.	LayerView
	Removes a group of handles owned by the object.	Accessor
	The method to implement that is responsible of drawing the content of the layer.	BaseLayerView2D
	The LayerView can call this method to ask the MapView to schedule a new rendering frame.	BaseLayerView2D
	Method to implement, which notifies of tiles being added or removed for the current view state.	BaseLayerView2D
Promise	`when()` may be leveraged once an instance of the class is created.	LayerView

Method Details

addHandles Inherited Method addHandles(handleOrHandles, groupKey) Inherited from Accessor 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

handleOrHandles WatchHandle|WatchHandle []

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.

attach Method attach()

Method called when after the LayerView is created and right before it's asked to draw the layer's content. Typically this method is implemented to start watching property changes on the layer for example.

See also

detach()

Example

attach() {
  this._propertyHandle = reactiveUtils.watch(
    () => this.layer.opacity,
    () => this.requestRender()
  );
}

detach Method detach()

Method called after the layer is removed and the LayerView is about to be removed. Typically, this method is implemented to free resources like watchers.

See also

attach()

Example

// remove the watchers on the layer that are added in attach()
detach() {
  this._propertyHandle.remove();
  this._propertyHandle = null;
}

hasHandles Inherited Method hasHandles(groupKey){Boolean} Inherited from Accessor 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");
}

hitTest Method hitTest(mapPoint, screenPoint){Promise<(ViewHit[]|null|undefined)>}

Method to implement that is responsible for providing objects hit at the specified screen coordinates. This method is called internally by the MapView each time its hitTest() method is called.

Parameters

mapPoint Point

The point in map units.

screenPoint ScreenPoint

The point in screen coordinates.

Returns

Type	Description
Promise<(ViewHit []\|null\|undefined)>	A Promise that resolves to an array of hits.

isFulfilled Inherited Method isFulfilled(){Boolean} Inherited from LayerView

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} Inherited from LayerView

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} Inherited from LayerView

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.

removeHandles Inherited Method removeHandles(groupKey) Inherited from Accessor 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 Method render(renderParameters)

The method to implement that is responsible of drawing the content of the layer. This method is called every time the MapView's state changes, or if requestRender() has been called.

Parameters

Specification

renderParameters Object

Specification

context CanvasRenderingContext2D

The canvas 2D context in which to draw content.

stationary Boolean

The stationary state of the MapView.

state ViewState

The object that describes view state.

pixelRatio Number

The pixel ratio.

Example

// Example of a render implementation that draws tile boundaries
render(renderParameters) {
  let tileSize = this.layer.tileInfo.size[0];
  let state = renderParameters.state;
  let pixelRatio = state.pixelRatio;
  let width = state.size[0];
  let height = state.size[1];
  let context = renderParameters.context;
  let coords = [0, 0];

  context.fillStyle = "rgba(0,0,0,0.25)";
  context.fillRect(0, 0, width * pixelRatio, height * pixelRatio);

  // apply rotation for everything that will be applied to the canvas
  if (state.rotation !== 0) {
    context.translate(width * pixelRatio * 0.5, height * pixelRatio * 0.5);
    context.rotate((state.rotation * Math.PI) / 180);
    context.translate(- width * pixelRatio * 0.5, -height * pixelRatio * 0.5);
  }

  // Set the style for all the text.
  context.font = "24px monospace";
  context.fillStyle = "black";
  context.shadowBlur = 1;

  for (const tile of this.tiles) {
    let screenScale = tile.resolution / state.resolution * pixelRatio;

    state.toScreenNoRotation(coords, tile.coords);

    // Draw the tile boundaries
    context.strokeRect(coords[0], coords[1], tileSize * screenScale, tileSize * screenScale);

    // Draw the tile information
    context.shadowColor = "white";
    context.fillText(
      tile.level + "/" + tile.row + "/" + tile.col + "/" + tile.world,
      coords[0] + 12,
      coords[1] + 24,
      tileSize * screenScale
    );
    context.shadowColor = "transparent";
  }
}

requestRender Method requestRender()

The LayerView can call this method to ask the MapView to schedule a new rendering frame.

Example

// Call requestRender whenever the layer opacity has changed.
attach() {
  this._propertyHandle = reactiveUtils.watch(
    () => this.layer.opacity,
    () => this.requestRender()
  );
}

tilesChanged Method tilesChanged(added, removed)

Method to implement, which notifies of tiles being added or removed for the current view state. This function can be implemented to start and stop fetching new data, or allocate and dispose resources.

Parameters

added Tile []

The tile objects added for the current view viewport.

removed Tile []

The tile objects removed from the view viewport.

when Inherited Method when(callback, errback){Promise} Inherited from LayerView

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

callback Function

optional

The function to call when the promise resolves.

errback Function

optional

The function to execute when the promise fails.

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 when() in the same way
let view = new MapView();
view.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
});

Type Definitions

ScreenPoint Type Definition ScreenPoint Since: ArcGIS Maps SDK for JavaScript 4.11 BaseLayerView2D since 4.8, ScreenPoint added at 4.11.

An object representing a point on the screen.

Properties: x Number

The x coordinate.

y Number

The y coordinate.

Tile Type Definition Tile Object

Represents a tile reference.

Properties: id String

The tile string identifier in the format level/row/col/world

level Number

The level identifier of the LOD to which the tile belongs

row Number

The row identifier.

col Number

The column identifier.

world Number

When the projection allows world wrapping (e.g. Web Mercator), identifies the instance of the world this tile's level/row/col.

resolution Number

The number of map units per pixel in the tile.

scale Number

The map scale at the tile's level.

coords Number []

The coordinates of the top-left corner of the tile as an array of two numbers. The coordinates are in un-normalized map units.

bounds Number []

The bounds of the tile as an array of four numbers that be readily converted to an Extent object.