How to get a untyped ObservableCollection from a DataContext?

Question

I need to get a untyped QueryableCollection from a DataContext to query it. I have the following code:

printAbleListView = (ListView) printObject.FindName("printAbleListView");
// Here I like to have something like ObservableCollection<Object>
ObservableCollection<Journal> allItems = (ObservableCollection<Journal>) printAbleListView.DataContext;

// Add the page to the page preview collection
for (int i = 0; i <= (allItems.Count()/30); i++)
{
  printAbleListView.DataContext = null;
  printAbleListView.DataContext = allItems.Skip(30 * i).Take(30);
  document.SetPreviewPage((i + 1), printObject);
}

The goal is to print out any ListView in a Metro-Style Windows 8 app. Currently it is typed to the Journal DataType, but I like to have it untyped so the function can be reused for every ListView, not only for the Journal ones. Hw can i archive this?

Answer 1

Example:

void GeneratePreview<T>(int itemsPerPage)
{
    var printAbleListView = (ListView)printObject.FindName("printAbleListView");
    var allItems = (ObservableCollection<T>)printAbleListView.DataContext;

    // Add the page to the page preview collection
    for (int i = 0; i <= (allItems.Count()/itemsPerPage); i++)
    {
      printAbleListView.DataContext =
              allItems.Skip(itemsPerPage * i).Take(itemsPerPage);
      document.SetPreviewPage((i + 1), printObject);
    }
}

---

For untyped access, you can actually use the fact that ObservableCollection<T> supports non-generic ICollection:

void GeneratePreview(int itemsPerPage)
{
    var printAbleListView = (ListView)printObject.FindName("printAbleListView");
    var allItems = (ICollection)printAbleListView.DataContext;

    var slice = new List<object>(itemsPerPage); // cannot use ArrayList for Win8 apps
    var pageNo = 1;
    foreach (var item in allItems)
    {            
        slice.Add(item);
        if (slice.Count % itemsPerPage == 0)
        {
            // flush
            printAbleListView.DataContext = slice;
            document.SetPreviewPage(pageNo, printObject);
            // and restart
            pageNo++;
            slice.Clear();
        }
    }
    if (slice.Count != 0) // flush the rest
    {
        printAbleListView.DataContext = slice;
        document.SetPreviewPage(pageNo, printObject);
    }
    // clean up
    printAbleListView.DataContext = null;
}