ArcGIS Pro 3.4 API Reference Guide
ArcGIS.Core.CIM Namespace / CIMBaseLayer Class / LayerMasks Property
Example Version

LayerMasks Property
Gets or sets the URIs of the layers used as masks.
Syntax
public string[] LayerMasks {get; set;}
Example
Mask feature
//Get the layer to be masked
var lineLyrToBeMasked = MapView.Active.Map.Layers.FirstOrDefault(lyr => lyr.Name == "TestLine") as FeatureLayer;
//Get the layer's definition
var lyrDefn = lineLyrToBeMasked.GetDefinition();
//Create an array of Masking layers (polygon only)
//Set the LayerMasks property of the Masked layer
lyrDefn.LayerMasks = new string[] { "CIMPATH=map3/testpoly.xml" };
//Re-set the Masked layer's defintion
lineLyrToBeMasked.SetDefinition(lyrDefn);
Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3 or higher.
See Also