public Guid TaskItemGuid {get;}

// get the first project task item
var taskItem = Project.Current.GetItems<TaskProjectItem>().FirstOrDefault();
// if there isn't a project task item, return
if (taskItem == null)
  return;

try
{
  // Open it
  //At 2.x -
  //System.Guid guid = await TaskAssistantModule.OpenTaskItemAsync(taskItem.TaskItemGuid);
  var guid = await TaskAssistantFactory.Instance.OpenTaskItemAsync(taskItem.TaskItemGuid);

  // TODO - retain the guid returned for use with CloseTaskItemAsync
}
catch (OpenTaskException e)
{
  ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show(e.Message);
}

// find the first project task item which is open
var taskItem = Project.Current.GetItems<TaskProjectItem>().FirstOrDefault(t => t.IsOpen == true);
// if there isn't a project task item, return
if (taskItem == null)
  return;

if (taskItem.IsOpen)
{
  // close it
  // NOTE : The task item will also be removed from the project
  //At 2.x -
  //TaskAssistantModule.CloseTaskAsync(taskItem.TaskItemGuid);
  TaskAssistantFactory.Instance.CloseTaskItemAsync(taskItem.TaskItemGuid);
}

// get the first project task item
var taskItem = Project.Current.GetItems<TaskProjectItem>().FirstOrDefault();
// if there isn't a project task item, return
if (taskItem == null)
  return;

try
{
  // export the task item to the c:\Temp folder
  string exportFolder = @"c:\temp";
  //At 2.x -
  //string fileName = await TaskAssistantModule.ExportTaskAsync(taskItem.TaskItemGuid, exportFolder);
  string fileName = await TaskAssistantFactory.Instance.ExportTaskItemAsync(taskItem.TaskItemGuid, exportFolder);
  ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show("Task saved to " + fileName);
}
catch (ExportTaskException e)
{
  ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show("Error saving task " + e.Message);
}