如何以有效的方式同步列表和可枚举？

Posted 2023-03-16

【中文标题】如何以有效的方式同步列表和可枚举？

【英文标题】：How to synchronize a list and an enumerable in an effective way?

【发布时间】：2014-09-11 01:27:52

【问题描述】：

我经常遇到问题，我需要在 C# 中同步两个列表。 例如，我有一个简单的字符串数组。 我想以一种非常简单的方式将这些字符串加载到 Listview 的 Items 列表中。我还想以最少的项目交换来更新列表视图。

示例：

 var strings = new List<string>()  "a", "b", "c", "d" ;
 listview1.Items.Synchronize(strings);
 strings.Add("xx");
 listview1.Items.Synchronize(strings); // just create a new item for xx

【参考方案1】：

我这里有一个简短的扩展函数，它可以同步两个不同类型的列表。 Lambda 扩展函数进行转换。 用法示例：

        listView1.Items.SyncList(strings, lvItem => lvItem.Tag as string, str => new ListViewItem(str)  Tag = str );

扩展函数定义如下：

    /// <summary>
    /// synchronizes an enumerable with a list with two different types, 
    /// </summary>
    /// <typeparam name="TSource">Type of the elements in the source list</typeparam>
    /// <typeparam name="TDestination">Type of the elements in the destination list</typeparam>
    /// <param name="source">Source</param>
    /// <param name="destination">Destination list</param>
    /// <param name="selector">returns the corresponding source object for the destination list item</param>
    /// <param name="creator">Creates new object for the destination list from the source. The selection function applied on the new object must return the source object. </param>
    public static void SyncList<TSource, TDestination>(this IList destination, IEnumerable<TSource> source, Func<TDestination, TSource> selector, Func<TSource, TDestination> creator)
        where TDestination : class
        where TSource : class
    
        if (source == null)
            throw new ArgumentNullException("source");

        if (destination == null)
            throw new ArgumentNullException("destination");

        if (selector == null)
            throw new ArgumentNullException("selector");

        if (creator == null)
            throw new ArgumentNullException("creator");

        var syncObject = destination.IsSynchronized ? destination.SyncRoot : new object();

        lock (syncObject)
        
            var ExistingItems = destination.OfType<TDestination>().Where(d => selector(d) != null).ToDictionary(d => selector(d));

            foreach (var s in source)
            
                if (!ExistingItems.Remove(s)) // s does not exist yet in the destination list
                
                    var NewObject = creator(s);

                    if (selector(NewObject) != s)
                        throw new ArgumentException("the selector must return the creation object of the new item");

                    destination.Add(creator(s));
                
            

            var RemovedItems = ExistingItems.Values;

            if (RemovedItems.Count == destination.Count)
                destination.Clear();
            else
                foreach (var i in RemovedItems)
                
                    destination.Remove(i);