public void AddAttachment( 
   MapMember mapMember,
   long oid,
   string filePath
)

//Chaining operations is a special case. Use "Chained Operations" when you require multiple transactions 
//to be undo-able with a single "Undo".

//The most common use case for operation chaining is creating a feature with an attachement. 
//Adding an attachment requires the object id (of a new feature) has already been created. 
var editOperation1 = new EditOperation();
editOperation1.Name = string.Format("Create point in '{0}'", CurrentTemplate.Layer.Name);

long newFeatureID = -1;
//The Create operation has to execute so we can get an object_id
var token2 = editOperation1.Create(this.CurrentTemplate, polygon);

//Must be within a QueuedTask
editOperation1.Execute(); //Note: Execute and ExecuteAsync will return true if the operation was successful and false if not
if (editOperation1.IsSucceeded)
{
  newFeatureID = (long)token2.ObjectID;
  //Now, because we have the object id, we can add the attachment.  As we are chaining it, adding the attachment 
  //can be undone as part of the "Undo Create" operation. In other words, only one undo operation will show on the 
  //Pro UI and not two.
  var editOperation2 = editOperation1.CreateChainedOperation();
  //Add the attachement using the new feature id
  editOperation2.AddAttachment(this.CurrentTemplate.Layer, newFeatureID, @"C:\data\images\Hydrant.jpg");
  //Execute the chained edit operation. editOperation1 and editOperation2 show up as a single Undo operation
  //on the UI even though we had two transactions
  editOperation2.Execute();
}