public void AddFilter( 
   BrowseProjectFilter filter
)

BrowseProjectFilter portalAndLocalProjectsFilter = new BrowseProjectFilter();
//A filter to pick projects from the portal
//This filter will allow selection of ppkx and portal project items on the portal
portalAndLocalProjectsFilter.AddFilter(BrowseProjectFilter.GetFilter("esri_browseDialogFilters_projects_online_proprojects"));
//A filter to pick projects from the local machine
portalAndLocalProjectsFilter.AddFilter(BrowseProjectFilter.GetFilter("esri_browseDialogFilters_projects"));
//Create the OpenItemDialog and set the filter to the one we just created
var openDlg = new OpenItemDialog()
{
  Title = "Select a Project",
  MultiSelect = false,
  BrowseFilter = portalAndLocalProjectsFilter
};
//Show the dialog
var result = openDlg.ShowDialog();
//Check if the user clicked OK and selected an item
bool? ok = openDlg.ShowDialog();
if (!ok.HasValue || openDlg.Items.Count() == 0)
  return; //nothing selected
var selectedItem = openDlg.Items.FirstOrDefault();
//Open the project use the OpenAsync method.