public class CIMLineSymbol : CIMMultiLayerSymbol, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

//Must be on QueuedTask.Run(() => { ...

//Build geometry
List<Coordinate2D> plCoords = new List<Coordinate2D>();
plCoords.Add(new Coordinate2D(1.5, 10.5));
plCoords.Add(new Coordinate2D(1.25, 9.5));
plCoords.Add(new Coordinate2D(1, 10.5));
plCoords.Add(new Coordinate2D(0.75, 9.5));
plCoords.Add(new Coordinate2D(0.5, 10.5));
plCoords.Add(new Coordinate2D(0.5, 1));
plCoords.Add(new Coordinate2D(0.75, 2));
plCoords.Add(new Coordinate2D(1, 1));
Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

//Set symbolology, create and add element to layout
CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(
          ColorFactory.Instance.BlackRGB, 2.0, SimpleLineStyle.Solid);
//var graphic = GraphicFactory.Instance.CreateShapeGraphic(linePl, lineSym);

var ge = ElementFactory.Instance.CreateGraphicElement(
                        container, linePl, lineSym, "New Freehand");

//Create a simple 2D line graphic and apply an existing line
//style item as the symbology.

//Construct on the worker thread
await QueuedTask.Run(() =>
{
  //Build 2d line geometry
  List<Coordinate2D> plCoords = new List<Coordinate2D>();
  plCoords.Add(new Coordinate2D(1, 8.5));
  plCoords.Add(new Coordinate2D(1.66, 9));
  plCoords.Add(new Coordinate2D(2.33, 8.1));
  plCoords.Add(new Coordinate2D(3, 8.5));
  //At 2.x - Polyline linePl = PolylineBuilder.CreatePolyline(plCoords);
  Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

  //(optionally) Reference a line symbol in a style
  StyleProjectItem lnStylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                                .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  SymbolStyleItem lnSymStyleItm = lnStylePrjItm.SearchSymbols(
                                StyleItemType.LineSymbol, "Line with 2 Markers")[0];
  CIMLineSymbol lineSym = lnSymStyleItm.Symbol as CIMLineSymbol;
  lineSym.SetSize(20);

  //Set symbolology, create and add element to layout

  //An alternative simple symbol is also commented out below.
  //This would elminate the four optional lines of code above that
  //reference a style.
  //
  //CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(
  //         ColorFactory.Instance.BlueRGB, 4.0, SimpleLineStyle.Solid);  
  //At 2.x - GraphicElement lineElm =
  //        LayoutElementFactory.Instance.CreateLineGraphicElement(
  //                                            layout, linePl, lineSym);

  GraphicElement lineElm = ElementFactory.Instance.CreateGraphicElement(
                                              container, linePl, lineSym);
  lineElm.SetName("New Line");
});

CIMLineSymbol lineSymbol = SymbolFactory.Instance.ConstructLineSymbol(ColorFactory.Instance.BlueRGB, 4.0, SimpleLineStyle.Solid);

CIMStroke stroke = SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.BlackRGB, 2.0);
CIMLineSymbol lineSymbolFromStroke = SymbolFactory.Instance.ConstructLineSymbol(stroke);

//These methods must be called within the lambda passed to QueuedTask.Run
var lineStrokeRed = SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.RedRGB, 4.0);
var markerCircle = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.RedRGB, 12, SimpleMarkerStyle.Circle);
markerCircle.MarkerPlacement = new CIMMarkerPlacementOnVertices()
{
  AngleToLine = true,
  PlaceOnEndPoints = true,
  Offset = 0
};
var lineSymbolWithCircles = new CIMLineSymbol()
{
  SymbolLayers = new CIMSymbolLayer[2] { markerCircle, lineStrokeRed }
};

//These methods must be called within the lambda passed to QueuedTask.Run
var markerTriangle = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.RedRGB, 12, SimpleMarkerStyle.Triangle);
markerTriangle.Rotation = -90; // or -90
markerTriangle.MarkerPlacement = new CIMMarkerPlacementOnLine() { AngleToLine = true, RelativeTo = PlacementOnLineRelativeTo.LineEnd };

var lineSymbolWithArrow = new CIMLineSymbol()
{
  SymbolLayers = new CIMSymbolLayer[2] { markerTriangle,
              SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.RedRGB, 2)
          }
};

/// <summary>
/// Create a line symbol with the markers placed at a 45 degree angle. <br/>  
/// ![LineSymbolAngleMarker](http://Esri.github.io/arcgis-pro-sdk/images/Symbology/line-marker-angle.png)
/// </summary>
/// <returns></returns>
internal static Task<CIMLineSymbol> CreateMyMarkerLineSymbolAsync()
{
  return QueuedTask.Run<CIMLineSymbol>(() =>
  {
    //Create a marker from the "|" character.  This is the marker that will be used to render the line layer.
    var lineMarker = SymbolFactory.Instance.ConstructMarker(124, "Agency FB", "Regular", 12);

    //Default line symbol which will be modified 
    var blackSolidLineSymbol = SymbolFactory.Instance.ConstructLineSymbol(ColorFactory.Instance.BlackRGB, 2, SimpleLineStyle.Solid);

    //Modifying the marker to align with line
    //First define "markerplacement"
    CIMMarkerPlacementAlongLineSameSize markerPlacement = new CIMMarkerPlacementAlongLineSameSize()
    {
      AngleToLine = true,
      PlacementTemplate = new double[] { 5 }
    };
    //assign the markerplacement to the marker
    lineMarker.MarkerPlacement = markerPlacement;
    //angle the marker if needed
    lineMarker.Rotation = 45;

    //assign the marker as a layer to the line symbol
    blackSolidLineSymbol.SymbolLayers[0] = lineMarker;

    return blackSolidLineSymbol;
  });
}

/// <summary>
/// Create a line symbol with a dash and two markers.<br/>          
/// </summary>
/// <remarks>
/// This line symbol comprises three symbol layers listed below: 
/// 1. A solid stroke that has dashes.
/// 1. A circle marker.
/// 1. A square marker.
/// ![LineSymbolTwoMarkers](http://Esri.github.io/arcgis-pro-sdk/images/Symbology/line-dash-two-markers.png)
/// </remarks>
/// <returns></returns>
internal static Task<CIMLineSymbol> CreateLineDashTwoMarkersAync()
{
  return QueuedTask.Run<CIMLineSymbol>(() =>
  {

    var dash2MarkersLine = new CIMLineSymbol();

    var mySymbolLyrs = new CIMSymbolLayer[]
          {
                new CIMSolidStroke()
                {
                    Color = ColorFactory.Instance.BlackRGB,
                    Enable = true,
                    ColorLocked = true,
                    CapStyle = LineCapStyle.Round,
                    JoinStyle = LineJoinStyle.Round,
                    LineStyle3D = Simple3DLineStyle.Strip,
                    MiterLimit = 10,
                    Width = 1,
                    CloseCaps3D = false,
                    Effects = new CIMGeometricEffect[]
                    {
                        new CIMGeometricEffectDashes()
                        {
                            CustomEndingOffset = 0,
                            DashTemplate = new double[] {20, 10, 20, 10},
                            LineDashEnding = LineDashEnding.HalfPattern,
                            OffsetAlongLine = 0,
                            ControlPointEnding = LineDashEnding.NoConstraint
                        },
                        new CIMGeometricEffectOffset()
                        {
                            Method = GeometricEffectOffsetMethod.Bevelled,
                            Offset = 0,
                            Option = GeometricEffectOffsetOption.Fast
                        }
                    },
                },
                CreateCircleMarkerPerSpecs(),
                CreateSquareMarkerPerSpecs()
      };
    dash2MarkersLine.SymbolLayers = mySymbolLyrs;
    return dash2MarkersLine;
  });
}
private static CIMMarker CreateCircleMarkerPerSpecs()
{
  var circleMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlackRGB, 5, SimpleMarkerStyle.Circle) as CIMVectorMarker;
  //Modifying the marker to align with line
  //First define "markerplacement"
  CIMMarkerPlacementAlongLineSameSize markerPlacement = new CIMMarkerPlacementAlongLineSameSize()
  {
    AngleToLine = true,
    Offset = 0,
    Endings = PlacementEndings.Custom,
    OffsetAlongLine = 15,
    PlacementTemplate = new double[] { 60 }
  };
  //assign the markerplacement to the marker
  circleMarker.MarkerPlacement = markerPlacement;
  return circleMarker;
}
private static CIMMarker CreateSquareMarkerPerSpecs()
{
  var squareMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlueRGB, 5, SimpleMarkerStyle.Square) as CIMVectorMarker;
  CIMMarkerPlacementAlongLineSameSize markerPlacement2 = new CIMMarkerPlacementAlongLineSameSize()
  {
    AngleToLine = true,
    Endings = PlacementEndings.Custom,
    OffsetAlongLine = 45,
    PlacementTemplate = new double[] { 60 },
  };
  squareMarker.MarkerPlacement = markerPlacement2;
  return squareMarker;
}

/// <summary>
/// Create a line symbol with a dash and two markers. <br/>
/// In this pattern of creating this symbol, a [CIMVectorMarker](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic6176.html) object is created as a new [CIMSymbolLayer](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic5503.html).
/// The circle and square markers created by [ContructMarker](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic12350.html) method is then assigned to the [MarkerGraphics](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic6188.html) property of the CIMVectorMarker. 
/// When using this method, the CIMVectorMarker's [Frame](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic6187.html) property needs to be set to the [CIMMarker](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic3264.html) object's Frame. 
/// Similarly, the CIMVectorMarker's [Size](https://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic3284.html) property needs to be set to the CIMMarker object's size.
/// </summary>
/// <remarks>
/// This line symbol comprises three symbol layers listed below: 
/// 1. A solid stroke that has dashes.
/// 1. A circle marker.
/// 1. A square marker.
/// ![LineSymbolTwoMarkers](http://Esri.github.io/arcgis-pro-sdk/images/Symbology/line-dash-two-markers.png)
/// </remarks>
/// <returns></returns>

internal static Task<CIMLineSymbol> CreateLineDashTwoMarkers2Async()
{
  return QueuedTask.Run<CIMLineSymbol>(() =>
  {
    //default line symbol that will get modified.
    var dash2MarkersLine = new CIMLineSymbol();
    //circle marker to be used in our line symbol as a layer
    var circleMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlackRGB, 5, SimpleMarkerStyle.Circle) as CIMVectorMarker;
    //circle marker to be used in our line symbol as a layer
    var squareMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlueRGB, 5, SimpleMarkerStyle.Square) as CIMVectorMarker;
    //Create the array of layers that make the new line symbol
    CIMSymbolLayer[] mySymbolLyrs =
          {
                new CIMSolidStroke() //dash line
                {
                    Color = ColorFactory.Instance.BlackRGB,
                    Enable = true,
                    ColorLocked = true,
                    CapStyle = LineCapStyle.Round,
                    JoinStyle = LineJoinStyle.Round,
                    LineStyle3D = Simple3DLineStyle.Strip,
                    MiterLimit = 10,
                    Width = 1,
                    CloseCaps3D = false,
                    Effects = new CIMGeometricEffect[]
                    {
                        new CIMGeometricEffectDashes()
                        {
                            CustomEndingOffset = 0,
                            DashTemplate = new double[] {20, 10, 20, 10},
                            LineDashEnding = LineDashEnding.HalfPattern,
                            OffsetAlongLine = 0,
                            ControlPointEnding = LineDashEnding.NoConstraint
                        },
                        new CIMGeometricEffectOffset()
                        {
                            Method = GeometricEffectOffsetMethod.Bevelled,
                            Offset = 0,
                            Option = GeometricEffectOffsetOption.Fast
                        }
                    }
                },
                new CIMVectorMarker() //circle marker
                {
                    MarkerGraphics = circleMarker.MarkerGraphics,
                    Frame = circleMarker.Frame, //need to match the CIMVector marker's frame to the circleMarker's frame.
                    Size = circleMarker.Size,    //need to match the CIMVector marker's size to the circleMarker's size.                    
                   MarkerPlacement = new CIMMarkerPlacementAlongLineSameSize()
                   {
                       AngleToLine = true,
                       Offset = 0,
                       Endings = PlacementEndings.Custom,
                       OffsetAlongLine = 15,
                       PlacementTemplate = new double[] {60},
                   }

                },
                new CIMVectorMarker() //square marker
                {
                   MarkerGraphics = squareMarker.MarkerGraphics,
                   Frame = squareMarker.Frame, //need to match the CIMVector marker's frame to the squareMarker frame.
                   Size = squareMarker.Size, //need to match the CIMVector marker's size to the squareMarker size.
                   MarkerPlacement = new CIMMarkerPlacementAlongLineSameSize()
                   {
                       AngleToLine = true,
                       Endings = PlacementEndings.Custom,
                       OffsetAlongLine = 45,
                       PlacementTemplate = new double[] {60},
                   }
                }
      };
    dash2MarkersLine.SymbolLayers = mySymbolLyrs;
    return dash2MarkersLine;
  });

}

/// <summary>
/// Create a polygon symbol with a diagonal cross hatch fill. <br/>
/// ![PolygonSymbolDiagonalCrossHatch](http://Esri.github.io/arcgis-pro-sdk/images/Symbology/polygon-diagonal-crosshatch.png)
/// </summary>
/// <returns></returns>
public static Task<CIMPolygonSymbol> CreateDiagonalCrossPolygonAsync()
{
  return QueuedTask.Run<CIMPolygonSymbol>(() =>
  {
    var trans = 50.0;//semi transparent
    CIMStroke outline = SymbolFactory.Instance.ConstructStroke(CIMColor.CreateRGBColor(0, 0, 0, trans), 2.0, SimpleLineStyle.Solid);

    //Stroke for the fill
    var solid = SymbolFactory.Instance.ConstructStroke(CIMColor.CreateRGBColor(255, 0, 0, trans), 1.0, SimpleLineStyle.Solid);

    //Mimic cross hatch
    CIMFill[] diagonalCross =
              {
                new CIMHatchFill() {
                    Enable = true,
                    Rotation = 45.0,
                    Separation = 5.0,
                    LineSymbol = new CIMLineSymbol() { SymbolLayers = new CIMSymbolLayer[1] { solid } }
                },
                new CIMHatchFill() {
                    Enable = true,
                    Rotation = -45.0,
                    Separation = 5.0,
                    LineSymbol = new CIMLineSymbol() { SymbolLayers = new CIMSymbolLayer[1] { solid } }
                }
      };
    List<CIMSymbolLayer> symbolLayers = new List<CIMSymbolLayer>
      {
                outline
      };
    foreach (var fill in diagonalCross)
      symbolLayers.Add(fill);
    return new CIMPolygonSymbol() { SymbolLayers = symbolLayers.ToArray() };
  });
}