我们如何从 IObservable<IList<T>> 创建一个 IObservableList<T>？

Question

问题

我们如何从IObservable<IReadOnlyList<T>> 到IObservableList<T>（从DynamicData）？

上下文

我在我的项目中同时使用了Reactive extensions 和DynamicData。

我目前有一个随时间变化的字符串列表。我有IObservable<IReadOnlyList<string>>。它会产生如下更新：

1. ["A", "C", "F"]
2. ["A", "B", "C", "F"]
3. ["A", "B", "C"]

我想将其转换为IObservableList<string>，它会产生如下更新：

1. 在索引 0 处添加“A”、“C”、“F”
2. 在索引 1 处添加“B”
3. 从索引 3 中删除“F”

我尝试过的

我尝试使用 ToObservableChangeSet 扩展，但它的行为不适合我的情况。

代码

Subject<IReadOnlyList<string>> source = new Subject<IReadOnlyList<string>>();
IObservable<IEnumerable<string>> observableOfList = source;
IObservable<IChangeSet<string>> observableOfChangeSet = source.ToObservableChangeSet<string>();

observableOfChangeSet
    .Bind(out ReadOnlyObservableCollection<string> boundCollection)
    .Subscribe();

((INotifyCollectionChanged)boundCollection).CollectionChanged += OnCollectionChanged;

source.OnNext(new[] { "A", "C", "F" });
source.OnNext(new[] { "A", "B", "C" });

void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    Debug.WriteLine($"[{string.Join(", ", (IEnumerable<string>)sender)}] (operation: {e.Action} at index {e.NewStartingIndex})");
}

输出

[A, C, F] (operation: Reset at index -1)
[A, C, F, A] (operation: Add at index 3)
[A, C, F, A, B] (operation: Add at index 4)
[A, C, F, A, B, C] (operation: Add at index 5)

我们可以看到[A, C, F, A, B, C] 与[A, B, C] 不同。

---

我也尝试过使用EditDiff，但这并不能保留列表的顺序。

代码

Subject<IReadOnlyList<string>> source = new Subject<IReadOnlyList<string>>();
IObservable<IEnumerable<string>> observableOfList = source;
IObservable<IChangeSet<string>> observableOfChangeSet = ObservableChangeSet.Create<string>(list =>
{
    return observableOfList
        .Subscribe(items => list.EditDiff(items, EqualityComparer<string>.Default));
});

observableOfChangeSet
    .Bind(out ReadOnlyObservableCollection<string> boundCollection)
    .Subscribe();

((INotifyCollectionChanged)boundCollection).CollectionChanged += OnCollectionChanged;

source.OnNext(new[] { "A", "C", "F" });
source.OnNext(new[] { "A", "B", "C" });

void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    Debug.WriteLine($"[{string.Join(", ", (IEnumerable<string>)sender)}] (operation: {e.Action} at index {e.NewStartingIndex})");
}

输出

[A, C, F] (operation: Reset at index -1)
[A, C] (operation: Remove at index -1)
[A, C, B] (operation: Add at index 2)

我们可以看到[A, C, B] 与[A, B, C] 不同。

谢谢！

Answer 1

如果字符串是唯一的，为什么不使用ToObservableChangeSet 的重载将字符串设置为键。这样，如果您的新列表不包含“F”，它就知道应该删除您现有的“F”。

也许有更简单的方法，但您可能需要暂时插入自己的索引。如果您不需要通过绑定集合跟踪更改，则可以从变更集中执行如下操作：

Subject<IReadOnlyList<string>> source = new Subject<IReadOnlyList<string>>();
IObservable<IEnumerable<string>> observableOfList = source;
IObservable<IChangeSet<(string,int),string>> observableOfChangeSet = source.Select(x => 
            {
                return x.Select((item, index) => (item, index));
            }).ToObservableChangeSet<(string,int),string>(x=>x.Item1);

observableOfChangeSet
    .Sort(SortExpressionComparer<(string, int)>.Ascending(x => x.Item2))
    .OnItemAdded(x=> Debug.WriteLine($"Item {x.Item1} was added to index {x.Item2}"))
    .OnItemRemoved(x => Debug.WriteLine($"Item {x.Item1} was removed from index {x.Item2}"))
    .OnItemUpdated((x,prev) => Debug.WriteLine($"Item {prev.Item1} at index {prev.Item2} was updated to Item {x.Item1} at index {x.Item2}"))
    .Transform(x=>
        {
            Debug.WriteLine($"Item: {x.Item1} at index: {x.Item2}");
           return x.Item1;
        })
    .Bind(out ReadOnlyObservableCollection<string> boundCollection)
    .Subscribe();

source.OnNext(new[] { "A", "C", "F" });
source.OnNext(new[] { "A", "B", "C" });

此代码的调试输出：

Item A was added to index 0
Item C was added to index 1
Item F was added to index 2
Item: A at index: 0
Item: C at index: 1
Item: F at index: 2
Item B was added to index 1
Item F was removed from index 2
Item A at index 0 was updated to Item A at index 0
Item C at index 1 was updated to Item C at index 2
Item: A at index: 0
Item: B at index: 1
Item: C at index: 2

Answer 2

我对 DynamicData 不太熟悉，但我相信这会给出接近预期结果的结果：

using DynamicData;
using System;
using System.Collections.Generic;
using System.Reactive.Linq;
using System.Reactive.Subjects;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            Subject<IReadOnlyList<string>> source = new Subject<IReadOnlyList<string>>();

            var list = ObservableChangeSet.Create<string>(sourceList =>
            {
                return source
                    .Subscribe(newItems =>
                    {
                        sourceList.Edit(items =>
                        {
                            for (var i = 0; i < newItems.Count; i++)
                            {
                                if (items.Count <= i) items.Add(newItems[i]);
                                else
                                {
                                    if (items[i] != newItems[i])
                                    {
                                        items[i] = newItems[i];
                                    }
                                }
                            }
                            while (items.Count > items.Count) items.RemoveAt(items.Count - 1);
                        });
                    });
            }).AsObservableList();

            source.OnNext(new[] { "A", "C", "F" });
            source.OnNext(new[] { "A", "B", "C", "F" });
            source.OnNext(new[] { "A", "B", "C" });

            Console.ReadLine();
        }
    }
}

很遗憾，我没有弄清楚如何获取Add "B" at index 1，但当前输出如下：

1. AddRange. 3 changes
2. 3 Changes
   • Replace. Current: B, Previous: C
   • Replace. Current: C, Previous: F
   • Add. Current: F, Previous: <None>
3. Remove. Current: C, Previous: <None>

编辑：以下给出了您想要的确切输出，但我没有测试每个的性能（对于较大的列表，插入可能会变得昂贵）：

using DynamicData;
using System;
using System.Collections.Generic;
using System.Reactive.Linq;
using System.Reactive.Subjects;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            Subject<IReadOnlyList<string>> source = new Subject<IReadOnlyList<string>>();

            var list = ObservableChangeSet.Create<string>(sourceList =>
            {
                return source
                    .Subscribe(newItems =>
                    {
                        sourceList.Edit(items =>
                        {
                            for (var i = 0; i < newItems.Count; i++)
                            {
                                if (items.Count <= i) items.Add(newItems[i]);
                                else
                                {
                                    if (items[i] != newItems[i])
                                    {
                                        items.Insert(i, newItems[i]);
                                    }
                                }
                            }
                            while (items.Count > newItems.Count) items.RemoveAt(items.Count - 1);
                        });
                    });
            }).AsObservableList();

            source.OnNext(new[] { "A", "C", "F" });
            source.OnNext(new[] { "A", "B", "C", "F" });
            source.OnNext(new[] { "A", "B", "C" });

            Console.ReadLine();
        }
    }
}

1. AddRange. 3 changes
2. Add. Current: B, Previous: <None> Index 1
3. Remove. Current: C, Previous: <None> Index 2