/// <summary>
/// Creates an observable collection whose content reflects the content of the specified collection, filtered by the specified predicate and mapped by the specified selector.
/// This collection is kept up-to-date with respect to changes in the original colletion.
/// </summary>
public static MyReadOnlyObservableCollection <TResult> WhereSelectLive <T, TResult>(this IReadOnlyObservableCollection <T> collection, Func <T, bool> predicate, Func <T, TResult> selector)
{
Contract.Requires(collection != null);
Contract.Requires(selector != null);
var result = new ProperObservableCollection <TResult>();
collection.CollectionChanged += collectionChanged;
collectionChanged(collection, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, collection));
return(new MyReadOnlyObservableCollection <TResult>(result));
void collectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
Contract.Requires(sender == collection);
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
result.InsertRange(e.NewStartingIndex, e.NewItems.Cast <T>().Where(predicate).Select(selector));
break;
case NotifyCollectionChangedAction.Remove:
result.RemoveRange(e.OldStartingIndex, e.OldItems.Count);
break;
case NotifyCollectionChangedAction.Replace:
result.Replace(e.OldStartingIndex, e.OldItems.Count, e.NewItems.Cast <T>().Where(predicate).Select(selector));
break;
case NotifyCollectionChangedAction.Move:
result.MoveRange(e.OldStartingIndex, e.OldItems.Count, e.NewStartingIndex);
break;
case NotifyCollectionChangedAction.Reset:
result.Clear();
break;
default:
throw new ArgumentException("No defined NotifyCollectionChangedEventArgs.Action specified", nameof(e));
}
}
}
private static void collectionChanged <T, TResult>(NotifyCollectionChangedEventArgs e, ProperObservableCollection <TResult> result, Func <T, TResult> selector)
{
Contract.Requires(e != null);
Contract.Requires(result != null);
Contract.Requires(selector != null);
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
if (e.NewStartingIndex == -1)
{
result.AddRange(e.NewItems.Cast <T>().Select(selector));
}
else
{
result.InsertRange(e.NewStartingIndex, e.NewItems.Cast <T>().Select(selector));
}
break;
case NotifyCollectionChangedAction.Remove:
result.RemoveRange(e.OldStartingIndex, e.OldItems.Count);
break;
case NotifyCollectionChangedAction.Replace:
result.Replace(e.OldStartingIndex, e.OldItems.Count, e.NewItems.Cast <T>().Select(selector));
break;
case NotifyCollectionChangedAction.Move:
result.MoveRange(e.OldStartingIndex, e.OldItems.Count, e.NewStartingIndex);
break;
case NotifyCollectionChangedAction.Reset:
result.Clear();
break;
default:
throw new ArgumentException("No defined NotifyCollectionChangedEventArgs.Action specified", nameof(e));
}
}
/// <summary>
/// Creates an observable collection whose content reflects the content of the specified collection, filtered by the specified predicate and mapped by the specified many selector.
/// This collection is kept up-to-date with respect to changes in the original colletion.
/// </summary>
public static MyReadOnlyObservableCollection <TResult> WhereSelectManyLive <T, TResult>(this ObservableCollection <T> collection, Func <T, bool> predicate, Func <T, IEnumerable <TResult> > selector)
{
Contract.Requires(collection != null);
Contract.Requires(selector != null);
List <int> elementCountsPerSourceElement = new List <int>();
int cumulativeElements(int sourceElementIndex)
{
return(elementCountsPerSourceElement.Take(sourceElementIndex).Sum());
}
var result = new ProperObservableCollection <TResult>();
collection.CollectionChanged += collectionChanged;
collectionChanged(collection, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, collection));
return(new MyReadOnlyObservableCollection <TResult>(result));
void collectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
Contract.Requires(sender == collection);
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
{
int sourceItemIndex = e.NewStartingIndex;
int resultIndex = cumulativeElements(e.NewStartingIndex);
foreach (var newSourceItem in e.NewItems.Cast <T>().Where(predicate))
{
int originalResultCount = result.Count;
result.InsertRange(resultIndex, selector(newSourceItem));
int selectedElementCount = result.Count - originalResultCount;
resultIndex += selectedElementCount;
elementCountsPerSourceElement.Insert(sourceItemIndex++, selectedElementCount);
}
break;
}
case NotifyCollectionChangedAction.Remove:
{
int resultIndex = cumulativeElements(e.OldStartingIndex);
int resultToRemoveCount = elementCountsPerSourceElement.Skip(e.OldStartingIndex).Take(e.OldItems.Count).Sum();
result.RemoveRange(resultIndex, resultToRemoveCount);
elementCountsPerSourceElement.RemoveRange(e.OldStartingIndex, e.OldItems.Count);
break;
}
case NotifyCollectionChangedAction.Replace:
result.Replace(e.OldStartingIndex, e.OldItems.Count, e.NewItems.Cast <T>().Where(predicate).SelectMany(selector));
break;
case NotifyCollectionChangedAction.Move:
result.MoveRange(e.OldStartingIndex, e.OldItems.Count, e.NewStartingIndex);
break;
case NotifyCollectionChangedAction.Reset:
result.Clear();
break;
default:
throw new ArgumentException("No defined NotifyCollectionChangedEventArgs.Action specified", nameof(e));
}
}
}
