问题
I have below ObservableCollection<string>. I need to sort this alphabetically.
private ObservableCollection<string> _animals = new ObservableCollection<string>
{
"Cat", "Dog", "Bear", "Lion", "Mouse",
"Horse", "Rat", "Elephant", "Kangaroo", "Lizard",
"Snake", "Frog", "Fish", "Butterfly", "Human",
"Cow", "Bumble Bee"
};
I tried _animals.OrderByDescending. But I don't know how to use it correctly.
_animals.OrderByDescending(a => a.<what_is_here_?>);
How can I do this?
回答1:
Introduction
Basically, if there is a need to display a sorted collection, please consider using the CollectionViewSource class: assign ("bind") its Source property to the source collection — an instance of the ObservableCollection<T> class.
The idea is that CollectionViewSource class provides an instance of the CollectionView class. This is kind of "projection" of the original (source) collection, but with applied sorting, filtering, etc.
References:
- How to: Sort and Group Data Using a View in XAML.
- WPF’s CollectionViewSource.
Live Shaping
WPF 4.5 introduces "Live Shaping" feature for CollectionViewSource.
References:
- WPF 4.5 New Feature: Live Shaping.
- CollectionViewSource.IsLiveSorting Property.
- Repositioning data as the data's values change (Live shaping).
Solution
If there still a need to sort an instance of the ObservableCollection<T> class, here is how it can be done.
The ObservableCollection<T> class itself does not have sort method. But, the collection could be re-created to have items sorted:
// Animals property setter must raise "property changed" event to notify binding clients.
// See INotifyPropertyChanged interface for details.
Animals = new ObservableCollection<string>
{
"Cat", "Dog", "Bear", "Lion", "Mouse",
"Horse", "Rat", "Elephant", "Kangaroo",
"Lizard", "Snake", "Frog", "Fish",
"Butterfly", "Human", "Cow", "Bumble Bee"
};
...
Animals = new ObservableCollection<string>(Animals.OrderBy(i => i));
Additional details
Please note that OrderBy() and OrderByDescending() methods (as other LINQ–extension methods) do not modify the source collection! They instead create a new sequence (i.e. a new instance of the class that implements IEnumerable<T> interface). Thus, it is necessary to re-create the collection.
回答2:
I know this is an old question, but is the first google result for "sort observablecollection" so thought it worth to leave my two cent.
The way
The way I would go is to build a List<> starting from the ObservableCollection<>, sort it (through its Sort() method, more on msdn) and when the List<> has been sorted, reorder the ObservableCollection<> with the Move() method.
The code
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);
}
}
The test
public void TestObservableCollectionSortExtension()
{
var observableCollection = new ObservableCollection<int>();
var maxValue = 10;
// Populate the list in reverse mode [maxValue, maxValue-1, ..., 1, 0]
for (int i = maxValue; i >= 0; i--)
{
observableCollection.Add(i);
}
// Assert the collection is in reverse mode
for (int i = maxValue; i >= 0; i--)
{
Assert.AreEqual(i, observableCollection[maxValue - i]);
}
// Sort the observable collection
observableCollection.Sort((a, b) => { return a.CompareTo(b); });
// Assert elements have been sorted
for (int i = 0; i < maxValue; i++)
{
Assert.AreEqual(i, observableCollection[i]);
}
}
Notes
This is just a proof of concept, showing how to sort an ObservableCollection<> without breaking the bindings on items.The sort algorithm has room for improvements and validations (like index checking as pointed out here).
回答3:
I created an extension method to the ObservableCollection
public static void MySort<TSource,TKey>(this ObservableCollection<TSource> observableCollection, Func<TSource, TKey> keySelector)
{
var a = observableCollection.OrderBy(keySelector).ToList();
observableCollection.Clear();
foreach(var b in a)
{
observableCollection.Add(b);
}
}
It seems to work and you don't need to implement IComparable
回答4:
I looked at these, I was getting it sorted, and then it broke the binding, as above. Came up with this solution, though simpler than most of yours, it appears to do what I want to,,,
public static ObservableCollection<string> OrderThoseGroups( ObservableCollection<string> orderThoseGroups)
{
ObservableCollection<string> temp;
temp = new ObservableCollection<string>(orderThoseGroups.OrderBy(p => p));
orderThoseGroups.Clear();
foreach (string j in temp) orderThoseGroups.Add(j);
return orderThoseGroups;
}
回答5:
This is an ObservableCollection<T>, that automatically sorts itself upon a change, triggers a sort only when necessary, and only triggers a single move collection change action.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
namespace ConsoleApp4
{
using static Console;
public class SortableObservableCollection<T> : ObservableCollection<T>
{
public Func<T, object> SortingSelector { get; set; }
public bool Descending { get; set; }
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
base.OnCollectionChanged(e);
if (SortingSelector == null
|| e.Action == NotifyCollectionChangedAction.Remove
|| e.Action == NotifyCollectionChangedAction.Reset)
return;
var query = this
.Select((item, index) => (Item: item, Index: index));
query = Descending
? query.OrderBy(tuple => SortingSelector(tuple.Item))
: query.OrderByDescending(tuple => SortingSelector(tuple.Item));
var map = query.Select((tuple, index) => (OldIndex:tuple.Index, NewIndex:index))
.Where(o => o.OldIndex != o.NewIndex);
using (var enumerator = map.GetEnumerator())
if (enumerator.MoveNext())
Move(enumerator.Current.OldIndex, enumerator.Current.NewIndex);
}
}
//USAGE
class Program
{
static void Main(string[] args)
{
var xx = new SortableObservableCollection<int>() { SortingSelector = i => i };
xx.CollectionChanged += (sender, e) =>
WriteLine($"action: {e.Action}, oldIndex:{e.OldStartingIndex},"
+ " newIndex:{e.NewStartingIndex}, newValue: {xx[e.NewStartingIndex]}");
xx.Add(10);
xx.Add(8);
xx.Add(45);
xx.Add(0);
xx.Add(100);
xx.Add(-800);
xx.Add(4857);
xx.Add(-1);
foreach (var item in xx)
Write($"{item}, ");
}
}
}
Output:
action: Add, oldIndex:-1, newIndex:0, newValue: 10
action: Add, oldIndex:-1, newIndex:1, newValue: 8
action: Move, oldIndex:1, newIndex:0, newValue: 8
action: Add, oldIndex:-1, newIndex:2, newValue: 45
action: Add, oldIndex:-1, newIndex:3, newValue: 0
action: Move, oldIndex:3, newIndex:0, newValue: 0
action: Add, oldIndex:-1, newIndex:4, newValue: 100
action: Add, oldIndex:-1, newIndex:5, newValue: -800
action: Move, oldIndex:5, newIndex:0, newValue: -800
action: Add, oldIndex:-1, newIndex:6, newValue: 4857
action: Add, oldIndex:-1, newIndex:7, newValue: -1
action: Move, oldIndex:7, newIndex:1, newValue: -1
-800, -1, 0, 8, 10, 45, 100, 4857,
回答6:
The argument to OrderByDescending is a function returning a key to sort with. In your case, the key is the string itself:
var result = _animals.OrderByDescending(a => a);
If you wanted to sort by length for example, you'll write:
var result = _animals.OrderByDescending(a => a.Length);
回答7:
_animals.OrderByDescending(a => a.<what_is_here_?>);
If animals would be a list of object Animal, you could use a property to order the list.
public class Animal
{
public int ID {get; set;}
public string Name {get; set;}
...
}
ObservableCollection<Animal> animals = ...
animals = animals.OrderByDescending(a => a.Name);
回答8:
myObservableCollection.ToList().Sort((x, y) => x.Property.CompareTo(y.Property));
回答9:
This extension method eliminates the need to sort the entire list.
Instead, it inserts each new item in place.
So the list is always remains sorted.
It turns out that this method just works when a lot of the other methods fail due to missing notifications when the collection changes. And it is rather fast.
To use:
// Call on dispatcher.
ObservableCollection<MyClass> collectionView = new ObservableCollection<MyClass>();
var p1 = new MyClass() { Key = "A" }
var p2 = new MyClass() { Key = "Z" }
var p3 = new MyClass() { Key = "D" }
collectionView.InsertInPlace(p1, o => o.Key);
collectionView.InsertInPlace(p2, o => o.Key);
collectionView.InsertInPlace(p3, o => o.Key);
// The list will always remain ordered on the screen, e.g. "A, D, Z" .
// Insertion speed is Log(N) as it uses a binary search.
And the extension method:
/// <summary>
/// Inserts an item into a list in the correct place, based on the provided key and key comparer. Use like OrderBy(o => o.PropertyWithKey).
/// </summary>
public static void InsertInPlace<TItem, TKey>(this ObservableCollection<TItem> collection, TItem itemToAdd, Func<TItem, TKey> keyGetter)
{
int index = collection.ToList().BinarySearch(keyGetter(itemToAdd), Comparer<TKey>.Default, keyGetter);
collection.Insert(index, itemToAdd);
}
And the binary search extension method:
/// <summary>
/// Binary search.
/// </summary>
/// <returns>Index of item in collection.</returns>
/// <notes>This version tops out at approximately 25% faster than the equivalent recursive version. This 25% speedup is for list
/// lengths more of than 1000 items, with less performance advantage for smaller lists.</notes>
public static int BinarySearch<TItem, TKey>(this IList<TItem> collection, TKey keyToFind, IComparer<TKey> comparer, Func<TItem, TKey> keyGetter)
{
if (collection == null)
{
throw new ArgumentNullException(nameof(collection));
}
int lower = 0;
int upper = collection.Count - 1;
while (lower <= upper)
{
int middle = lower + (upper - lower) / 2;
int comparisonResult = comparer.Compare(keyToFind, keyGetter.Invoke(collection[middle]));
if (comparisonResult == 0)
{
return middle;
}
else if (comparisonResult < 0)
{
upper = middle - 1;
}
else
{
lower = middle + 1;
}
}
// If we cannot find the item, return the item below it, so the new item will be inserted next.
return lower;
}
回答10:
/// <summary>
/// Sorts the collection.
/// </summary>
/// <typeparam name="T">The type of the elements of the collection.</typeparam>
/// <param name="collection">The collection to sort.</param>
/// <param name="comparison">The comparison used for sorting.</param>
public static void Sort<T>(this ObservableCollection<T> collection, Comparison<T> comparison = null)
{
var sortableList = new List<T>(collection);
if (comparison == null)
sortableList.Sort();
else
sortableList.Sort(comparison);
for (var i = 0; i < sortableList.Count; i++)
{
var oldIndex = collection.IndexOf(sortableList[i]);
var newIndex = i;
if (oldIndex != newIndex)
collection.Move(oldIndex, newIndex);
}
}
This solution is based on Marco's answer. I had some problems with his solution and therefore improved it by only calling Move if the index actually changed. This should improve performance and also fix the linked issue.
回答11:
I did a sort on a certain class field (distance).
public class RateInfo
{
public string begin { get; set; }
public string end { get; set; }
public string price { get; set; }
public string comment { get; set; }
public string phone { get; set; }
public string ImagePath { get; set; }
public string what { get; set; }
public string distance { get; set; }
}
public ObservableCollection<RateInfo> Phones { get; set; }
public List<RateInfo> LRate { get; set; }
public ObservableCollection<RateInfo> Phones { get; set; }
public List<RateInfo> LRate { get; set; }
......
foreach (var item in ph)
{
LRate.Add(new RateInfo { begin = item["begin"].ToString(), end = item["end"].ToString(), price = item["price"].ToString(), distance=kilom, ImagePath = "chel.png" });
}
LRate.Sort((x, y) => x.distance.CompareTo(y.distance));
foreach (var item in LRate)
{
Phones.Add(item);
}
回答12:
Here is a slight variation on Shimmy's one for collection of classes that already implement the well-known IComparable<T> interface. In this case, the "order by" selector is implicit.
public class SortedObservableCollection<T> : ObservableCollection<T> where T : IComparable<T>
{
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
base.OnCollectionChanged(e);
if (e.Action != NotifyCollectionChangedAction.Reset &&
e.Action != NotifyCollectionChangedAction.Move &&
e.Action != NotifyCollectionChangedAction.Remove)
{
var query = this.Select((item, index) => (Item: item, Index: index)).OrderBy(tuple => tuple.Item, Comparer.Default);
var map = query.Select((tuple, index) => (OldIndex: tuple.Index, NewIndex: index)).Where(o => o.OldIndex != o.NewIndex);
using (var enumerator = map.GetEnumerator())
{
if (enumerator.MoveNext())
{
base.MoveItem(enumerator.Current.OldIndex, enumerator.Current.NewIndex);
}
}
}
}
// (optional) user is not allowed to move items in a sorted collection
protected override void MoveItem(int oldIndex, int newIndex) => throw new InvalidOperationException();
protected override void SetItem(int index, T item) => throw new InvalidOperationException();
private class Comparer : IComparer<T>
{
public static readonly Comparer Default = new Comparer();
public int Compare(T x, T y) => x.CompareTo(y);
}
// explicit sort; sometimes needed.
public virtual void Sort()
{
if (Items.Count <= 1)
return;
var items = Items.ToList();
Items.Clear();
items.Sort();
foreach (var item in items)
{
Items.Add(item);
}
OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
来源：https://stackoverflow.com/questions/19112922/sort-observablecollectionstring-through-c-sharp