有没有办法从ObservableCollection获得范围？

Question

I would like to get a range from an ObservableCollection for the purpose of looping through it and changing a property on those items. Is there an easy built-in way to do this with the ObservableCollection class?

Answer 1

You can use Skip and Take .

System.Collections.ObjectModel.ObservableCollection<int> coll = 
    new System.Collections.ObjectModel.ObservableCollection<int>()
        { 1, 2, 3, 4, 5 };
foreach (var i in coll.Skip(2).Take(2))
{
    Console.WriteLine(i);
}

Answer 2

For looping, ObservableCollection<T> derives from Collection<T> , and implements IList<T> . This lets you loop by index:

for (int i=5;i<10;++i)
{
     DoSomething(observableCollection[i]);
}

If you want to do queries on the collection via LINQ, you have a couple of options. You can use Skip() and Take() , or build a new range and access by index:

var range = Enumerable.Range(5, 5);
var results = range.Select(i => DoMappingOperation(observableCollection[i]));

Or:

var results = observableCollection.Skip(5).Take(5).Select(c => DoMappingOperation(c));

Answer 3

ObservableCollection<T> implements Colletion<T> which implements IEnumerable so you should be able to do (if you're looking for a range that matches a given criteria):

foreach(var item in observerableCollection.Where(i => i.prop == someVal))
{
    item.PropertyToChange = newValue;
}

Or an arbitrary range (in this case it takes items 10 - 40):

foreach(var item in observableCollection.Skip(10).Take(30))
{
    item.PropertyToChange = newValue;
}

Answer 4

foreach(var item in MyObservableProperty.Skip(10).Take(20))
{
  item.Value = "Second ten";
}

Skip and Take are linq extension methods used for paging a collection.