Is Clearing ObservableCollection Recommended before Adding Items to it?

Question

I often need to filter an ObservableCollection that already have items in it. Which approach is better?

// Assigning the filtered result directly
FilteredObservableCol = FilteredCollectionCopy.Where(i=> i.Age > 25).ToObservableCollection();

Or

// Clearing the collection first
FilteredObservableCol.Clear();
FilteredObservableCol = FilteredCollectionCopy.Where(i=> i.Age > 25).ToObservableCollection();

Your snippets won't compile. So neither is better. That said, if you're planning to re-assign the field with new instance --you don't need to clear the old list. — Sriram Sakthivel, Apr 19 '16 at 19:08

Michael Mairegger · Answer 1 · 2016-04-20T06:21:15.160

2

You could use CollectionViewSources instead of the ObservableCollection to bind to. There you can apply filtering.

ICollectionView MyCollection { get; private set; }

public void LoadData()
{
    var myObservable = //... load/create list
    MyCollection = CollectionViewSource.GetDefaultView(myObservable);
    MyCollection.Filter = item => ((TypeOfItem)item).Name = "bob";
}

edited Apr 20 '16 at 06:21

answered Apr 19 '16 at 19:18

Michael Mairegger

6,503
28
40

What "myobservable" would be in this case? – usefulBee Apr 19 '16 at 19:45
@usefulBee the initial `ObservableCollection` – Michael Mairegger Apr 19 '16 at 19:47
A little confusing. I thought MyCollection will completely replace MyObservableCollection. So you are saying that MyObservableCollection will remain bound to the view but the sorting will take place in MyCollection. Is that correct? thx – usefulBee Apr 19 '16 at 19:52
1

@usefulBee I have changed the code a bit to, hopefully, clarify it. You bind to MyCollection, myObservable should not be not visible in XAML – Michael Mairegger Apr 19 '16 at 19:55
I keep getting error, "Cannot implicitly convert type ICollectionView to CollectionViewSource" – usefulBee Apr 19 '16 at 20:05
1

Sorry, my bad. It is ICollectionView not ICollectionViewSource. – Michael Mairegger Apr 19 '16 at 20:07
The other problem is that "i.Name", "i.Age" etc are not recognized as a valid properties. An example: var myObservable = new List(); MyCollection in this case does not pick the MySchool type, so it won't deliver properties which kind of make sense. – usefulBee Apr 19 '16 at 20:37
@usefulBee cast `item` to the type it really is; see, edited code – Michael Mairegger Apr 20 '16 at 06:21

Is Clearing ObservableCollection Recommended before Adding Items to it?

1 Answers1