Question

我试图派生两个ObservableCollections的联合，并且联合中的项目不是唯一的。

using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Linq;

namespace ObservableCollectionUnion
{
    class Program
    {
        class Option { public string Code; }

        static void Main(string[] args)
        {
            Option[] opts1 = {
                new Option { Code = "1" },
                new Option { Code = "2" },
            };
            Option[] opts2 = {
                new Option { Code = "2" },
                new Option { Code = "3" },
            };
            ObservableCollection<Option> obsOpts1 = new ObservableCollection<Option>(opts1);
            ObservableCollection<Option> obsOpts2 = new ObservableCollection<Option>(opts2);
            ObservableCollection<Option> obsOptsBoth = new ObservableCollection<Option>(obsOpts1.Union(obsOpts2));

            foreach (Option opt in obsOptsBoth) {
                Debug.WriteLine(opt.Code);
            }
        }
    }
}

输出为：

我如何获得1,2,3？我尝试传递IComparer或IEqualityComparer，但出现错误

Error   CS1929  'ObservableCollection<Program.Option>' does not contain a definition for 'Union' and the best extension method overload 'Queryable.Union<Program.Option>(IQueryable<Program.Option>, IEnumerable<Program.Option>, IEqualityComparer<Program.Option>)' requires a receiver of type 'IQueryable<Program.Option>'

这就是我要处理的事情

using System;
using System.Collections;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Linq;

namespace ObservableCollectionUnion
{
    class Program
    {
        class Option { public string Code; }

        class OptionComparer : IEqualityComparer
        {
            public new bool Equals(object x, object y)
            {
                return Convert.ToInt32(((Option)x).Code) == Convert.ToInt32(((Option)y).Code);
            }

            public int GetHashCode(object obj)
            {
                return ((Option)obj).Code.GetHashCode();
            }
        }

        static void Main(string[] args)
        {
            Option[] opts1 = {
                new Option { Code = "1" },
                new Option { Code = "2" },
            };
            Option[] opts2 = {
                new Option { Code = "2" },
                new Option { Code = "3" },
            };
            ObservableCollection<Option> obsOpts1 = new ObservableCollection<Option>(opts1);
            ObservableCollection<Option> obsOpts2 = new ObservableCollection<Option>(opts2);
            ObservableCollection<Option> obsOptsBoth = new ObservableCollection<Option>(obsOpts1.Union(obsOpts2, new OptionComparer()));

            foreach (Option opt in obsOptsBoth) {
                Debug.WriteLine(opt.Code);
            }
        }
    }
}

有趣的是，我正在遵循智能感知告诉我的内容。它说ObservableCollection.Union的签名是

    public static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second, IEqualityComparer<TSource> comparer);

Answer 1

它不会返回重复项。如果您做了类似的事情

var commonOption = new Option { Code = "2" }

并将其用于可观察的集合中，它将按预期工作。默认情况下，仅当它们是同一实例时，类才相等。如果需要其他种类的相等性，可以通过覆盖相等性运算符来定义它。

两个ObservableCollections的并集返回重复项

1 个答案: