Ordering xamarin forms observable collection

1
votes

In xamarin forms do I have a Oberservable collection of wordpress posts.

I want to sort this collection by a specific value within this collection?

How am I able to do so in Xamarin forms / c# ?

I can see somewhere are people using:

list.OrderByDescending(x => DateTime.Parse(x)).ToList();

But this does not use a Observable collection or a specific value from this collection to sort.

The fill of my object is this: 

FlowObservableCollection<RootObject2> result = JsonConvert.DeserializeObject<FlowObservableCollection<RootObject2>>(await posts.Content.ReadAsStringAsync());

Does anyone have a solution for sorting my array?

My value I wanna sort by is a sub value like: mycollection.group.Myvalue

Thanks in advance!

2
c#xamlxamarinxamarin.forms
It would help if you could tell me on what basis do you want to sort this collection - FreakyAli

2 Answers

3
votes

I am not familiar with FlowObservableCollection<T> but from what I could find it seems to be a subtype of ObservableCollection<T>Microsoft Docs.

Since ObservableCollection<T> itself is a subtype of Collection<T> and therefore implements IEnumerable<T> you should not have any problem using its extension methods, e.g. OrderBy.

I can see somewhere are people using:

list.OrderByDescending(x => DateTime.Parse(x)).ToList();

My value I wanna sort by is a sub value like: mycollection.group.Myvalue

Are you familiar with lambda expressions as used in the LINQ query of your OrderByDescending() example?

In case your not, in list.OrderByDescending(x => DateTime.Parse(x)).ToList(); the term x refers to an element in the list and what your specify to the right of the => arrow is your key for ordering.

So if you wanto to order by a different value you could simply write something like myCollection.OrderByDescending(x => x.MyProperty); Note that you can use terms different from x as long as they are the same on both sides of the arrow, e.g. myCollection.OrderByDescending(myElement => myElement.MyProperty);

Finally note that the call to myCollection.OrderByDescending() returns a new IEnumerable with the elements found in myCollection and does not change myCollection itself.

You cannot cast IEnumerable<T> to FlowObservableCollection<T>. So if you need an ordered FlowObservableCollection<T> you have to instantiate a new one using your ordered IEnumerable as an input.

In your case this is what it might look like:

var orderedElements = myCollection.OrderByDescending(x => x.MyProperty); 
var orderedCollection = new FlowObservableCollection<RootObject2>(orderedElements);`
2
votes

You can try this:

   Collection = new ObservableCollection(Collection.OrderBy(x=>x.Date).ToList());

Or adapt this method:

public static void Sort<T>(this ObservableCollection<T> collection, Comparison<T> comparison)
{
    var sortableList = new List<T>(collection);
    sortableList.Sort(comparison);

    for (int i = 0; i < sortableList.Count; i++)
    {
        collection.Move(collection.IndexOf(sortableList[i]), i);
    }
}