I want to check the Count of an IEnumerable but it's very inneficient. Any help?

Question

Special thanks to Rex M for this bit of wisdom:

        public IEnumerable<Friend> FindFriends()
        {
            //Many thanks to Rex-M for his help with this one.
            //http://stackoverflow.com/users/67/rex-m

            return doc.Descendants("user").Select(user => new Friend
            {
                ID = user.Element("id").Value,
                Name = user.Element("name").Value,
                URL = user.Element("url").Value,
                Photo = user.Element("photo").Value
            });
        }

After finding all of a users friends, I need to show them on a WPF form. I have a problem that not all users have at least 5 friends, some even have no friends! Here's what I have:

        private void showUserFriends()
        {
            if (friendsList.ToList().Count > 0)
            {
                friend1.Source = new BitmapImage(new Uri(friendsList.ToList()[0].Photo));
                label11.Content = friendsList.ToList()[0].Name;

                friend2.Source = new BitmapImage(new Uri(friendsList.ToList()[1].Photo));
                label12.Content = friendsList.ToList()[1].Name;

                //And so on, two more times. I want to show 4 friends on the window.
            }            
        }

So this question has two parts:

1. How do you suggest I handle the varying number of friends a user might have. With my current code if a user has no friends I get an IndexOutOfBounds exception because friendsList[0] doesn't exist.

2. How can I more efficiently handle the validation of whether or not a user has friends? Calling .ToList() seems very taxing.

Answer 1

1) Databind the friends list to a ListBox. You can use data templates to display images and labels.

2) Call Any().

Answer 2

In this case just call ToList() once before the if statement rather than creating a list everytime.

EDIT

You might want to look at the MVVM pattern and have XAML to bind the controls to the data

Answer 3

Use some kind of ItemContainer control, such as any ItemsControl. You just specify a template for what the item should look like, and set its ItemsSource property:

myItemsControl.ItemsSource = new ObservableCollection(myFriends.Take(4));

This will show up to 4 friends, repeating the template as many times as it needs to, but as few as 0 if the collection is empty.

Answer 4

When you call ToList() on an IEnumerable what you are doing is Enumerating all the elements of the enumerable list and placing the results into a container. So a "code smell" is code that call's ToList() multiple times on the same IEnumerable, it should only be done once and saved to a variable.

There is a simple rule of thumb. If you are operating on the IEnumerable list as a whole (Linq expressions) or simply navigating the list from start to finish then use IEnumerable, if you need to access a list by index, or count the number of elements or navigate both directions through the list, create a List container first and use it.

i.e.

List<Friend> friends = FindFriends().ToList();
//Then use the friends list....

Now, with regards to if there is anything in your list or not, as a couple people here have mentioned, you can use data binding and a control like ItemsControl, but if you do want to build UI stuff up dynamically use a loop, don't index into the array.

List<Friend> friends = FindFriends().ToList();
if(friends.Count > 0)
{
  foreach(Friend f in friends)
  {
    //Create your Control(s) and add them to your form or panel's controls container
    // somthing like (untested) myPanel.Controls.Add(new Label(){Text = f.Name});
  }
}