Handling dummy items in ObservableCollection

Question

In my WPF application I need to implement the drag and drop functionality like windows explorer shell. I have had a look at canvas and it was pretty good but then since we wanted items to be aligned, went in to add dummy items into the ObservableCollection. Now I'm able to add dummy items in the ObservableCollection and also able to swap 2 items in Observable Collection. The problem is when the program starts, it takes time to load since I have added dummy items and on replacing items, a new ObservableCollection is generated which replaces the current Collection. So how do I increase the speed? Either I can fix this or may be I'm heading the wrong direction for replacing items. Can anyone advice?

Code to swap the ObservableCollection.

static ObservableCollection<T> Swap<T>(IList<T> list, int indexA, int indexB)
{
    if (indexA != -1 && indexB != -1)
    {
        T tmp = list[indexA];
        list[indexA]    = list[indexB];
        list[indexB]    = tmp;
    }
    return new ObservableCollection<T>(list);
}

This is how I call it:

AppsList = Swap<ItemTemplate>(AppsList, targetIndex, selectedIndex);

I need to improve User experience so that this delay is not noticed. If I can eliminate the delay,there's nothing like it.

score 2 · Accepted Answer · answered Mar 19 '14 at 17:14

2

Instead of replacing the entire ObservableCollection<T>, you can just mutate within the existing collection. When you replace the entire collection, the bindings for every element are refreshed - if you change the collection in place, only the changed elements get their bindings refreshed.

answered Mar 19 '14 at 17:14

Reed Copsey

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Reed,could you give a snippet? – Aster Veigas Mar 19 '14 at 17:52
@AsterVeigas Just use the guts of your existing method that swap elements, but do it directly on the existing `ObservableCollection` – Reed Copsey Mar 19 '14 at 17:53
Perfect. Thats what I need. How do I speed up my app in initially as I would be adding dummy items. Lazy loading the solution for ObservableCollection? – Aster Veigas Mar 19 '14 at 17:57
@AsterVeigas Yes - don't hook up the ObservableCollection to the property until the data is ready - that's typically the best option. – Reed Copsey Mar 19 '14 at 18:01

Handling dummy items in ObservableCollection

1 Answers1