AsyncFeatureLayer¶
Namespace: ThinkGeo.Core
A layer that draws features supplied by an AsyncFeatureSource.
public abstract class AsyncFeatureLayer : AsyncLayer
Inheritance object → LayerBase → AsyncLayer → AsyncFeatureLayer
Remarks:
This is the asynchronous counterpart to FeatureLayer, and it exists so that generic code has one type to write against whatever the source behind it is: a web service, a database driver with an asynchronous API, a source of your own.
Styling works exactly as it does on FeatureLayer: set styles on AsyncFeatureLayer.ZoomLevelSet. The bounding-box query every source can answer is here; for paging, counting or filtering, go to AsyncFeatureLayer.FeatureSource, where what is on offer depends on the source.
Nothing here knows about transport. A source that fetches over HTTP goes on a WebBasedAsyncFeatureLayer, which adds the client, proxy, credentials and timeout settings.
Properties¶
FeatureSource¶
Gets the source this layer draws from.
public abstract AsyncFeatureSource FeatureSource { get; }
Property Value¶
ConcurrentAccess¶
Gets or sets how this layer behaves when more than one thread wants to draw it at once. This is its AsyncFeatureLayer.FeatureSource's value, exactly as FeatureLayer does it.
public ConcurrentAccess ConcurrentAccess { get; set; }
Property Value¶
ZoomLevelSet¶
Gets or sets the styles used to draw this layer, banded by zoom level.
public ZoomLevelSet ZoomLevelSet { get; set; }
Property Value¶
DrawingMarginInPixel¶
Gets or sets how far beyond the visible extent features are requested, in pixels.
public float DrawingMarginInPixel { get; set; }
Property Value¶
Remarks:
A margin keeps symbols and labels that straddle the edge of the view from being clipped. FeatureLayer defaults to 50 because widening a query against a local file costs almost nothing; here the default is 0, because every pixel of margin is extra extent a remote source has to answer for on every redraw. Raise it when clipped symbols at the edge of the view matter more than the traffic.
ProjectionConverter¶
Gets or sets the converter applied between the source's coordinate system and the map's.
public ProjectionConverter ProjectionConverter { get; set; }
Property Value¶
Name¶
Gets or sets the display name for the layer.
public string Name { get; set; }
Property Value¶
string
The name used to identify the layer within UI components such as legends.
Remarks:
The name is user defined. Assign a descriptive value so tooling such as legends and layer lists can surface a meaningful label to end users.
IsOpen¶
Gets a value indicating whether the layer is currently open.
public bool IsOpen { get; }
Property Value¶
bool
true if the layer has completed its open routine; otherwise, false.
Remarks:
This method is the concrete wrapper for the abstract method IsOpenCore. Various methods on the Layer require that it be in an open state. If one of those methods is called when the state is not open, then the method will throw an exception. To enter the open state, you must call the Layer Open method. The method will raise an exception if the current Layer is already open.
As this is a concrete public method that wraps a Core method, we reserve the right to add events and other logic to pre- or post-process data returned by the Core version of the method. In this way, we leave our framework open on our end, but also allow you the developer to extend our logic to suit your needs. If you have questions about this, please contact our support team as we would be happy to work with you on extending our framework.
IsVisible¶
Gets or sets a value indicating whether the layer is visible.
public bool IsVisible { get; set; }
Property Value¶
bool
true to draw the layer; otherwise, false.
Remarks:
If this property is set to false, the layer will not draw. We ensure this in the Draw method. This is useful for legends and other controls that control the visibility of layers.
Projection¶
Gets the projection of the layer.
public Projection Projection { get; set; }
Property Value¶
DrawingExceptionMode¶
Gets or sets how drawing exceptions are handled when the layer renders.
public DrawingExceptionMode DrawingExceptionMode { get; set; }
Property Value¶
Background¶
Gets or sets the background color used when rendering the layer.
public GeoColor Background { get; set; }
Property Value¶
GeoColor
The fill applied to areas not covered by layer content.
Transparency¶
Gets or sets the amount of transparency applied to the rendered image.
public float Transparency { get; set; }
Property Value¶
float
A value between 0 (fully transparent) and 255 (fully opaque).
Opacity¶
Gets or sets the opacity applied to the rendered image.
public float Opacity { get; set; }
Property Value¶
float
A value between 0.0 (fully transparent) and 1.0 (fully opaque).
BlueTranslation¶
Gets or sets the intensity adjustment applied to the blue channel.
public float BlueTranslation { get; set; }
Property Value¶
float
A value between -255 and 255 representing the blue channel translation.
RedTranslation¶
Gets or sets the intensity adjustment applied to the red channel.
public float RedTranslation { get; set; }
Property Value¶
float
A value between -255 and 255 representing the red channel translation.
GreenTranslation¶
Gets or sets the intensity adjustment applied to the green channel.
public float GreenTranslation { get; set; }
Property Value¶
float
A value between -255 and 255 representing the green channel translation.
KeyColors¶
Gets the collection of key colors that should be rendered as transparent.
public Collection<GeoColor> KeyColors { get; }
Property Value¶
Remarks:
Attempting to access this collection when the associated GeoCanvas does not support key colors (see GeoCanvas.SupportKeyColor) results in an exception. Add colors to this collection to ensure they render as transparent.
IsNegative¶
Gets or sets a value indicating whether the image should be rendered with inverted colors.
public bool IsNegative { get; set; }
Property Value¶
bool
true to invert the color channels; otherwise, false.
IsGrayscale¶
Gets or sets a value indicating whether the image should be converted to grayscale prior to rendering.
public bool IsGrayscale { get; set; }
Property Value¶
bool
true to apply a grayscale filter; otherwise, false.
HasBoundingBox¶
Gets a value indicating whether the layer supports retrieving its bounding box.
public bool HasBoundingBox { get; }
Property Value¶
Remarks:
When this property is false, calls to or GetFullExtent throw an exception. The default implementation returns false.
ThreadSafe¶
Gets or sets the threading guarantees provided by the layer implementation.
public ThreadSafetyLevel ThreadSafe { get; set; }
Property Value¶
ThreadSafetyLevel
The level of thread safety that callers can expect when interacting with the layer.
Remarks:
Replaced by LayerBase.ConcurrentAccess and kept only so that code written against it is told, by name, what to use instead. It does not compile, so there is never a question of which of the two a caller meant: there is one value, and it is the other one. That matters because the translation was lossy in one direction - writing ThreadSafetyLevel.Unsafe could only pick ConcurrentAccess.UnsafeLock, and would silently undo a layer or source that had said ConcurrentAccess.UnsafeClone.
ColorMappings¶
Gets the color translation map that will be applied when rendering the layer.
public Dictionary<GeoColor, GeoColor> ColorMappings { get; }
Property Value¶
Dictionary<GeoColor, GeoColor>
WrappingMode¶
Gets or sets how the layer wraps when the map extent crosses world boundaries.
public WrappingMode WrappingMode { get; set; }
Property Value¶
WrappingExtent¶
Gets or sets the geographic extent to use when wrapping is enabled.
public RectangleShape WrappingExtent { get; set; }
Property Value¶
Methods¶
GetFeaturesInsideBoundingBoxAsync(RectangleShape, CancellationToken)¶
Returns the features that fall inside .
public Task<Collection<Feature>> GetFeaturesInsideBoundingBoxAsync(RectangleShape boundingBox, CancellationToken cancellationToken)
Parameters¶
boundingBox RectangleShape
The extent to query, in the map's projection.
cancellationToken CancellationToken
A token that cancels the operation.
Returns¶
Task<Collection<Feature>>
The features inside the bounding box.
Remarks:
Every source can answer this one, which is why it is here. For anything else - paging, counting, filtering on a column, addressing features by id - cast AsyncFeatureLayer.FeatureSource to the concrete source type and call it there; what is available depends on the source.
OpenAsyncCore(CancellationToken)¶
Opens the underlying feature source.
protected Task OpenAsyncCore(CancellationToken cancellationToken)
Parameters¶
cancellationToken CancellationToken
A token that cancels the operation.
Returns¶
Task
A task that represents the asynchronous operation.
OnPreparingDrawRequest(GeoCanvas)¶
Called before each draw-time feature request, so a derived layer can tell its source about the view it is drawing into.
protected void OnPreparingDrawRequest(GeoCanvas canvas)
Parameters¶
canvas GeoCanvas
The canvas about to be drawn on.
Returns¶
Remarks:
Most sources need nothing here. It exists for services that adapt a request to the display - ArcGIS Server, for instance, takes a geometry simplification tolerance derived from the current map resolution - without putting screen dimensions into the query signature that every source has to implement.
CloseAsyncCore(CancellationToken)¶
Closes the underlying feature source.
protected Task CloseAsyncCore(CancellationToken cancellationToken)
Parameters¶
cancellationToken CancellationToken
A token that cancels the operation.
Returns¶
Task
A task that represents the asynchronous operation.
DrawAsyncCore(GeoCanvas, Collection<SimpleCandidate>)¶
Requests the features in view and draws them with the styles for the current zoom level.
protected Task DrawAsyncCore(GeoCanvas canvas, Collection<SimpleCandidate> labelsInAllLayers)
Parameters¶
canvas GeoCanvas
The canvas to draw on.
labelsInAllLayers Collection<SimpleCandidate>
Label candidates already placed by other layers.
Returns¶
Task
A task that represents the asynchronous operation.
Remarks:
This mirrors FeatureLayer's drawing sequence, with the feature request awaited rather than blocking: pick the zoom level, ask it which columns its styles need, widen the extent by the drawing margin, fetch, then draw.
Events¶
DrawingException¶
Occurs when the DrawingException event is raised.
public event EventHandler<DrawingExceptionLayerEventArgs> DrawingException;
DrawnException¶
Occurs when the DrawnException event is raised.
public event EventHandler<DrawnExceptionLayerEventArgs> DrawnException;