Of all layers currently existing in a drawing only one can be active at a time. The currently active layer can be obtained from the ActiveLayer property of the NDrawingDocument class. For example:

// obtain the document active layer
NLayer activeLayer = document.ActiveLayer;

' obtain the document active layer
Dim activeLayer As NLayer = document.ActiveLayer

Drawings can have multiple layers, which are accessible from the Layers property. The active layer for a drawing is specified by the ActiveLayerUniqueId property of the NDrawingDocument class. The following code adds a new layer to a drawing document and makes it the currently active one:

// create a new layer and make it the active one
NLayer layer = new NLayer();
drawingDocument.Layers.AddChild(layer);
drawingDocument.Layers.ActiveLayerUniqueId = layer.UniqueId;

' create a new layer and make it the active one
Dim layer As New NLayer
drawingDocument.Layers.AddChild(layer)
drawingDocument.Layers.ActiveLayerUniqueId = layer.UniqueId

Layers implement the following features:

• Painting - layers implement the INPaintable interface. The implementation delegates the painting to the layer children. The layer visibility is controlled from its Visible property.
  

  C#	Copy Code
  // hide the active layer drawingDocument.ActiveLayer.Visible = false;

  Visual Basic	Copy Code
  ' hide the active layer drawingDocument.ActiveLayer.Visible = False

• Shadows - object shadows can be cast on a per layer basis. For example:
  

  C#	Copy Code
  // cast object shadows behind all nodes in this layer drawingDocument.ShadowsZOrder = ShadowsZOrder.BehindLayer;

  Visual Basic	Copy Code
  ' cast object shadows behind all nodes in this layer drawingDocument.ShadowsZOrder = ShadowsZOrder.BehindLayer

• Hit Tests  - you can hit test only the elements, which reside in a particular layer, hence NLayer implements the INHitTest interface.