Best way to set BIG IEnumerable as ListBox.ItemSource

Question

I'm trying to use a Microsoft.Windows.APICodePack.Shell.ShellContainer as ItemsSource for a ListBox, showing each child's (ShellObject) Thumbnail and Name via ListBox.ItemTemplate. The problem arises when ShellContainer refers to a VERY BIG folder (say more than one thousand files): if I simply declare

    ShellContainer source=ShellObject.FromParsingName(@"C:\MyFolder") as ShellContainer:
    listBox1.ItemsSource=source.GetEnumerator();

it freezes the UI for two or three minutes, then displays ShellContainer's content all at once. The best workaround I've found is to create an async filler class like this

class AsyncSourceFiller
{
    private ObservableCollection<ShellObject> source;
    private ShellContainer path;
    private Control parent;
    private ShellObject item;

    public AsyncSourceFiller(ObservableCollection<ShellObject> source, ShellContainer path, Control parent)
    {
        this.source = source;
        this.path = path;
        this.parent = parent;
    }

    public void Fill()
    {
        foreach (ShellObject obj in path)
        {
            item = obj;
            parent.Dispatcher.Invoke(new Action(Add));
            Thread.Sleep(4);
        }
    }

    private void Add()
    {
        source.Add(item);
    }
}

and then call it via

    ObservableCollection<ShellObject> source = new ObservableCollection<ShellObject>();
    listBox1.ItemsSource = source;
    ShellContainer path = ShellObject.FromParsingName(@"C:\MyFolder"):
    AsyncSourceFiller filler = new AsyncSourceFiller(source, path, this);
    Thread th = new Thread(filler.Fill);
    th.IsBackground = true;
    th.Start();

This takes more time than the previous way, but doesn't freeze the UI and begins to show some content immediately. Is there any better way to obtain a similar behavior, possibly shortening total operation time?

score 1 · Answer 1 · answered May 07 '12 at 07:41

1

load all data in background thread and when finished update itemssource of your listbox. and do not forget to set Virtualization to true in your listbox.

answered May 07 '12 at 07:41

blindmeis

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Thank you. Virtualization solves my problem, but as far as I know it is available only via VirtualizingStackPanel, and inside my ListBox I NEED a WrapPanel. I'm investigating about the feasibility of implementing one by myself, but it seems to be far beyond my humble skills, not to speak about third party options: or they are severely expensive, or they seem buggy and approximate... – italianogrosso May 07 '12 at 15:50

score 0 · Answer 2 · answered May 07 '12 at 08:02

The time consuming operation is to enumerate your ShellContainer and create thousands of ShellObject. ListBox is not the issue.

When you set an IEnumerable as source to an ItemControl, I think that it creates and internal list out of the enumerator the first time displayed, and that is why it freezes for two minutes before showing anything.

You do not have many options here:

Create yourself a List<ShellObject> and set it as source of our ListBox. It isn't faster but at least you can display a "Loading, please wait" message to your users.
Load the list in another thread (as you do) and display items as they load. It's a bit weird as the list "grows" over time.
Find a way to wrap your ShellContainer in a class that implements IList. For this, you need to be able to get an item at a given index in the ShellContainer class (I don't know "Windows API code pack"). If you use this as source of you ListBox and virtualization is enabled, only the displayed ShellObjects will be loaded, and it will be fast and smooth.

Thank you. Please tell me more about this IList interface, and how can it be of help in my case... — italianogrosso, May 07 '12 at 15:54

Best way to set BIG IEnumerable as ListBox.ItemSource

2 Answers2