• esri/views

BaseLayerView2D

AMD: require(["esri/views/2d/layers/BaseLayerView2D"], (BaseLayerView2D) => { /* code goes here */ });
ESM: import BaseLayerView2D from "@arcgis/core/views/2d/layers/BaseLayerView2D";
Class: esri/views/2d/layers/BaseLayerView2D
Inheritance: BaseLayerView2D LayerView Accessor
Since: ArcGIS Maps SDK for JavaScript 4.8

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

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 Working with Properties topic.
Show inherited properties Hide inherited properties
Name Type Summary Class
String

The name of the class.

more details
Accessor
Layer

References the layer this LayerView represents.

more details
BaseLayerView2D
Boolean

Indicates if the spatialReference of the MapView is supported by the layer view.

more details
LayerView
Boolean

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

more details
LayerView
Tile[]

The array of Tile objects computed to cover the MapView's visible area.

more details
BaseLayerView2D
Boolean

Value is true when the layer is updating; for example, if it is in the process of fetching data.

more details
LayerView
MapView

References the MapView this LayerView belongs to.

more details
BaseLayerView2D
Boolean

When true, the layer is visible in the view.

more details
LayerView

Property Details

declaredClass Stringreadonly inherited

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

layer Layer

References the layer this LayerView represents.

spatialReferenceSupported Booleanreadonly inherited
Since: ArcGIS Maps SDK for JavaScript 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 Booleanreadonly inherited

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

See also
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
updating Booleanreadonly inherited

Value is true when the layer is updating; for example, if it is in the process of fetching data.

Default Value:false
view MapView

References the MapView this LayerView belongs to.

visible Boolean inherited

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

Method Overview

Show inherited methods Hide inherited methods
Name Return Type Summary Class

Adds one or more handles which are to be tied to the lifecycle of the object.

more details
Accessor

Method called when after the LayerView is created and right before it's asked to draw the layer's content.

more details
BaseLayerView2D

Method called after the layer is removed and the LayerView is about to be removed.

more details
BaseLayerView2D
Boolean

Returns true if a named group of handles exist.

more details
Accessor
Promise<Graphic[]>

Method to implement that is responsible for providing objects hit at the specified screen coordinates.

more details
BaseLayerView2D
Boolean

isFulfilled() may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected).

more details
LayerView
Boolean

isRejected() may be used to verify if creating an instance of the class is rejected.

more details
LayerView
Boolean

isResolved() may be used to verify if creating an instance of the class is resolved.

more details
LayerView

Removes a group of handles owned by the object.

more details
Accessor

The method to implement that is responsible of drawing the content of the layer.

more details
BaseLayerView2D

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

more details
BaseLayerView2D

Method to implement, which notifies of tiles being added or removed for the current view state.

more details
BaseLayerView2D
Promise

when() may be leveraged once an instance of the class is created.

more details
LayerView

Method Details

addHandles(handleOrHandles, groupKey)inherited
Since: ArcGIS Maps SDK for JavaScript 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 }
);

// Handle gets removed when the object is destroyed.
this.addHandles(handle);
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 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
Example
attach() {
  this._propertyHandle = this.layer.watch("opacity", function() {
    this.requestRender();
  });
}
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
Example
// remove the watchers on the layer that are added in attach()
detach() {
  this._propertyHandle.remove();
  this._propertyHandle = null;
}
hasHandles(groupKey){Boolean}inherited
Since: ArcGIS Maps SDK for JavaScript 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(mapPoint, screenPoint){Promise<Graphic[]>}

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<Graphic[]> A Promise that resolves to an array of graphics.
isFulfilled(){Boolean}inherited

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(){Boolean}inherited

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(){Boolean}inherited

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(groupKey)inherited
Since: ArcGIS Maps SDK for JavaScript 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(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

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.

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()

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 = this.layer.watch("opacity", function() {
    this.requestRender();
  });
}
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(callback, errback){Promise}inherited

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
Since: ArcGIS Maps SDK for JavaScript 4.11

An object representing a point on the screen.

Properties
x Number

The x coordinate.

y Number

The y coordinate.

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.

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