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public class Person { public string Name { get; set; } public string Gender { get; set; } public int Age { get; set; } public List<Phone> Phones { get; set; } } public class Phone { public string Country { get; set; } public string City { get; set; } public string Name { get; set; } } static void Main(string[] args) { List<Person> PersonLists = new List<Person>() { new Person { Name = "张三",Age = 20,Gender = "男", Phones = new List<Phone> { new Phone { Country = "中国", City = "北京", Name = "小米" }, new Phone { Country = "中国",City = "北京",Name = "华为"}, new Phone { Country = "中国",City = "北京",Name = "联想"}, new Phone { Country = "中国",City = "台北",Name = "魅族"}, } }, new Person { Name = "松下",Age = 30,Gender = "男", Phones = new List<Phone> { new Phone { Country = "日本",City = "东京",Name = "索尼"}, new Phone { Country = "日本",City = "大阪",Name = "夏普"}, new Phone { Country = "日本",City = "东京",Name = "松下"}, } }, new Person { Name = "克里斯",Age = 40,Gender = "男", Phones = new List<Phone> { new Phone { Country = "美国",City = "加州",Name = "苹果"}, new Phone { Country = "美国",City = "华盛顿",Name = "三星"}, new Phone { Country = "美国",City = "华盛顿",Name = "HTC"} } } }; Console.WriteLine("这是该方法的第一种重载:"); var firstLists = PersonLists.Select(p => p.Name); foreach (var List in firstLists) { Console.WriteLine($"{List}"); } Console.WriteLine("这是该方法的第二种重载,就是加了一个索引项参数:"); var secondLists = PersonLists.Select((p, q) => { return (q.ToString() + p.Name); }); foreach (var List in secondLists) { Console.WriteLine($"{List}"); } Console.Read(); } 运行效果如下图所示： 接下来再看SelectMany()，SelectMany()就比较牛逼了，官方解释为将序列的每个元素投影到 IEnumerable<TResult> 并将结果序列合并为一个序列，先看代码和运行效果，代码如下： public class Person { public string Name { get; set; } public string Gender { get; set; } public int Age { get; set; } public List<Phone> Phones { get; set; } } public class Phone { public string Country { get; set; } public string City { get; set; } public string Name { get; set; } } static void Main(string[] args) { List<Person> PersonLists = new List<Person>() { new Person { Name = "张三",Age = 20,Gender = "男", Phones = new List<Phone> { new Phone { Country = "中国", City = "北京", Name = "小米" }, new Phone { Country = "中国",City = "北京",Name = "华为"}, new Phone { Country = "中国",City = "北京",Name = "联想"}, new Phone { Country = "中国",City = "台北",Name = "魅族"}, } }, new Person { Name = "松下",Age = 30,Gender = "男", Phones = new List<Phone> { new Phone { Country = "日本",City = "东京",Name = "索尼"}, new Phone { Country = "日本",City = "大阪",Name = "夏普"}, new Phone { Country = "日本",City = "东京",Name = "松下"}, } }, new Person { Name = "克里斯",Age = 40,Gender = "男", Phones = new List<Phone> { new Phone { Country = "美国",City = "加州",Name = "苹果"}, new Phone { Country = "美国",City = "华盛顿",Name = "三星"}, new Phone { Country = "美国",City = "华盛顿",Name = "HTC"} } } }; var Lists = PersonLists.SelectMany(p => p.Phones);//此方法的第一个重载 foreach (var list in Lists) { Console.WriteLine($"{list.Country} -- {list.City} --{list.Name}"); } Console.Read(); } selectMany可以将phones元素单独投影成为一个序列：。 运行效果如下所示： SelectMany()的第二种重载是这样的： public static IEnumerable<TResult> SelectMany<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, IEnumerable<TResult>> selector); 保持初始化实体类数据不变，编写第二种重载的代码： var Lists = PersonLists.SelectMany((p,i) => { p.Phones.ForEach(q => { q.Country += i.ToString(); }); return p.Phones; }); foreach (var list in Lists) { Console.WriteLine($"{list.Country} -- {list.City} --{list.Name}"); } Console.Read(); 其实无非是多了一个参数：索引，此索引为PersonLists的索引，上述代码会在Phone元素的Country属性中添加PersonLists的索引，返回类型依旧是，然后输出。运行效果如下图所示： SelectMany()的第三种重载是这样的： public static IEnumerable<TResult> SelectMany<TSource, TCollection, TResult>(this IEnumerable<TSource> source, Func<TSource, IEnumerable<TCollection>> collectionSelector, Func<TSource, TCollection, TResult> resultSelector) 看似十分复杂，无非就是返回一个自定义的匿名类，并且可以投影你想要的元素，编写第三种重载的代码： var Lists = PersonLists.SelectMany(p => p.Phones,(p,q) => new { PersonName = p.Name,PhoneName = q.Name }); foreach (var List in Lists) { Console.WriteLine($"{List.PersonName} -- {List.PhoneName}"); } Console.Read(); 以上代码的返回类型是这样的： 运行结果如下图所示： SelectMany()的第四种重载是这样的： public static IEnumerable<TResult> SelectMany<TSource, TCollection, TResult>(this IEnumerable<TSource> source, Func<TSource, int, IEnumerable<TCollection>> collectionSelector, Func<TSource, TCollection, TResult> resultSelector) 其实就是比第三种又多了一个PersonLists的索引而已，代码如下： var Lists = PersonLists.SelectMany((p,i) => { p.Phones.ForEach(q => { q.Name += i.ToString();}); return p.Phones; }, (p,q) => new { PersonName = p.Name,PhoneName = q.Name }); foreach (var List in Lists) { Console.WriteLine($"{List.PersonName} -- {List.PhoneName}"); } Console.Read(); 运行结果如下图所示： ———————————————— |
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