Advanced List usage (filter enumerable items)

I have a ListBox in my App. Also I have a collection of the items and each of this items have the collection of the items inside. So, actually it's a tree and I want to display them like folders/files.

class item
{
 ...
 List<item> childItems;
}

There are different types of items, some of them is not folders or files and I do not want to display them (all of them have the same base type).

So, I'm new in c#, but I feel that there should be the way to filter the items at runtime. Maybe when ListBox is trying to get the items from the List and fill itself, because I heard a little about the enumerable arrays in c#.

In c++ I fill the ListCtrl manually, but in c# there is a binding and it's cool. Currently I copy the items to ObservableCollection, filter the unwanted items and then use this collection as itemsSouce with ListBox. Maybe there is another way to filter items at runtime? I think that I should deliver my own List from the c# List and do something with enumerable interface, yep?

Answers


I'm not sure what exactly your filtering logic looks like but you could create a filtered property that you bind to like this...

class item
{
   ...
   List<item> childItems;

    public IEnumerable<item> FileSystemItems
    {
        get
        {
            return childItems.Where(x => x is IFile || x is IFolder);
        }
    }
}

EDIT: WP7.1 doesn't have IEnumerable.Where

I've hand edited this and can't compile it so bear with me... but wihtout using .Where it could look something like this...

    public List<item> FileSystemItems
    {
        get
        {
            var list = new List<item>();
            foreach (child in childItems)
            {
                if (child is IFile || child is IFolder)
                    list.Add(child);
            }
            return list;
        }
    }

Obviously replace IFile and IFolder with whatever your actual filter strategy looks like.

Your listbox binding will look something like this... (this is WPF but as far as I know silverlight is the same)

<ListBox ItemsSource="{Binding FileSystemItems}">

My full WPF binding looks like this..

<ListBox ItemsSource="{Binding FileSystemItems}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Name}"></TextBlock>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

You'll need to replace the... {Binding Name} part... replace Name with whatever property you want to display in your listbox... or you can leave that off if you aren't using an ItemTemplate.


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