ArcGIS Pro 2.8 API Reference Guide
Extent Property (MapView)
Example 

ArcGIS.Desktop.Mapping Namespace > MapView Class : Extent Property
Gets the current extent of the view.
Syntax
public Envelope Extent {get;}
Public ReadOnly Property Extent As Envelope
Remarks
Use this in combination with ZoomTo(Geometry,Nullable<TimeSpan>,Boolean) to get and set the view's extent.
Example
Expand the active map view's extent.
public Task<bool> ExpandExtentAsync(double dx, double dy)
{
  return QueuedTask.Run(() =>
  {
    //Get the active map view.
    var mapView = MapView.Active;
    if (mapView == null)
      return false;

    //Expand the current extent by the given ratio.
    var extent = mapView.Extent;
    var newExtent = ArcGIS.Core.Geometry.GeometryEngine.Instance.Expand(extent, dx, dy, true);
    return mapView.ZoomTo(newExtent);
  });
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

MapView Class
MapView Members