介绍    ·First - 返回集合中的第一个元素；不延迟    ·FirstOrDefault - 返回集合中的第一个元素（如果没有则返回默认值）；不延迟    ·Last - 返回集合中的最后一个元素；不延迟    ·LastOrDefault - 返回集合中的最后一个元素（如果没有则返回默认值）    ·ElementAt - 返回集合中指定索引的元素；不延迟    ·ElementAtOrDefault - 返回集合中指定索引的元素（如果没有则返回默认值）；不延迟    ·Contains - 判断集合中是否包含有某一元素；不延迟    ·Any - 判断集合中是否有元素满足某一条件；不延迟    ·All - 判断集合中是否所有元素都满足某一条件；不延迟    ·Count - 返回集合中的元素个数，返回int；不延迟    ·LongCount - 返回集合中的元素个数，返回long；不延迟    ·Sum - 集合应为数字类型集合，求其和；不延迟    ·Min - 返回集合的最小值；不延迟    ·Max - 返回集合的最大值；不延迟    ·Average - 集合应为数字类型集合，求其平均值；不延迟    ·Aggregate - 根据输入的表达式获取一个聚合值；不延迟    ·Cast - 将集合转换为强类型集合；延迟    ·DefaultIfEmpty - 查询结果为空则返回默认值；延迟    ·SequenceEqual - 判断两个集合是否相同；不延迟    ·OfType - 过滤集合中的指定类型；延迟    ·ToArray - 将集合转换为数组；不延迟    ·ToList - 将集合转换为List<T>集合；不延迟    ·ToDictionary - 将集合转换为<K, V>集合；不延迟

1. Selectselect 在一个集合序列按给定的条件进行投影，select 可以返回组合的筛选结果，返回匿名类型，对返回结果进行操作，返回组合的子查询结果等等。select 的方法定义原形为：public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)该扩展方法是在Enumerable类型中定义的:// 数据源的类型的属性var result = from student in DataSource.Students             where student.Name.Length > 3             select student.Name;// 数据源类型筛选后的结果var result = from student in DataSource.Students             where student.Name.Length > 3             select student;// 新类型var result = from student in DataSource.Students             where student.Name.Length > 3             select new Student { Name = student.Name, StudentID = student.StudentID };// 匿名类型var result = from student in DataSource.Students             where student.Name.Length > 3             select new { Name = student.Name, StudentID = student.StudentID };// 对返回结果进行操作var result = from student in DataSource.Students             where student.Name.Length > 3             select student.ToString();由Select方法原型可看出，返回结果为：IEnumerable<T>类型。2. SelectManySelectMany定义原型为：public static IEnumerable<TResult> SelectMany<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, IEnumerable<TResult>> selector)通过原型可以看出，筛选结果的每一个元素类型都应该实现IEnumerable<T>接口:string实现了IEnumerable<T>接口，可以构造这样的场景：查询组成学生姓名的所有字符序列。var result = DataSource.Students.SelectMany(str => str.Name);等价的Select 子句为：var result = from student in DataSource.Students             from ch in student.Name             select ch;可以认为SelectMany是将序列的每个元素投影到 IEnumerable<(Of <(T>)>) 并将结果序列合并为一个序列。3.Distinct原型为：public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source)去掉投影结果集的重复元素。该运算只能以方法调用的方式进行操作。上面同样的场景：查询组成学生姓名的所有字符的不重复序列。var result = DataSource.Students.SelectMany(str => str.Name).Distinct();4. First、Last、Skip、Take、SingleFirst 选择集和的第一个元素。var result = DataSource.Students.Select(student => student).First(); // Student ID:1,Student Name:AndyLast 选择集和的最后一个元素。var result = DataSource.Students.Select(student => student).Last(); // Student ID:4,Student Name:DarkSkip 跳过N个元素。var result = DataSource.Students.Select(student => student).Skip(2).Count(); // 2Take 选择集合的前N个元素。var result = DataSource.Students.Select(student => student).Skip(2).Take(1).Count(); // 1Single 返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。var result = DataSource.Students.Select(student => student).Single(); // 异常：Sequence contains more than one element5. OrderBy[Descending]对集合进行排序。public static IOrderedEnumerable<TSource> OrderBy[Descending]<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector[, IComparer<TKey> comparer])TKey必须已经实现了IComparer<T>接口。
方法1:var result = from student in DataSource.Students             orderby student.Name descending             select student.Name;方法2:var result = DataSource.Students.OrderByDescending(student => student.Name).Select(student => student.Name);
结果：// Dark// Cindy// Bill// Andy

public static class GameConstants{    public static readonly string SCENE_STARTER = "_Starter";    public static readonly string SCENE_MOVIETITLE = "MovieTitle";    public static readonly string SCENE_BATTLE_UI = "Battle_UI";    public static readonly string SCENE_BATTLE_RESULT_UI = "Battle_Result_UI";    public static readonly string[] SCENES;    // -----------------------------------------------------------    public static readonly string CHARACTER_IDLE_ANIMATION_NAME = "Idle";    public static readonly string CHARACTER_ATTACK_ANIMATION_NAME = "Attack";    public static readonly string CHARACTER_DEATH_ANIMATION_NAME = "Dead";    public static readonly string[] CHARACTER_ACTIONS;    // -----------------------------------------------------------    public static readonly string TAG_PLAYER_CHARACTER = "PlayerCharacter";    public static readonly string TAG_ENEMY_CHARACTER  = "EnemyCharacter";    public static readonly string[] TAGS;    // ==================================    static GameConstants()    {        SCENES = AggregatePublicStaticFields("SCENE_");        CHARACTER_ACTIONS = AggregatePublicStaticFields("CHARACTER_ACTIONS_");        TAGS = AggregatePublicStaticFields("TAG_");    }    private static string[] AggregatePublicStaticFields(string prefix)    {        var fields = typeof(GameConstants).GetFields(BindingFlags.Public | BindingFlags.Static);        return fields.Where(x => x.Name.StartsWith(prefix)).Select(x => (string)x.GetValue(null)).ToArray();    }}

  bool RetrieveFightZones()  {        var nodeTransform = stageInstance.transform.FindChildByPath(BattleConstants.StageConstants.FightZonesNodePath);        foreach (Transform fightZoneTransform in nodeTransform)        {             fightZoneTransform                .Cast<Transform>()              // 转化为Transform类型                .Select(x => x.gameObject)      // x代表转化后的transform 然后取它的Gameobject                .ToList()                       // 将GameObject转换为List<T>集合                .ForEach(GameObject.Destroy);   // 循环销毁gameObject        }   }

void UpdatePositions()
{         // 转化为Transform选择位置 然后转化为数组 输出      Positions = transform. Cast<Transform>() .Select(t => t.position) .ToArray();}  

void SetupPositions(){      // 转化为Transform 将当前位置 转化为数组返回      Positions = transform.Cast<Transform>().Select(x =>{var newPos = x.position; return newPos; }).ToArray();}

private IEnumerator InitializeBattleAsync(){    var charactersLoading = battleCharacterManager.CreateCharacters(
         //参数1 将数组创建的数组CharacterCreationInfo 和 DebugAddMoreCharacters函数的前三个返回的结果链接 然后转化成数组         new CharacterCreationInfo[]{new CharacterCreationInfo(CharacterType.Me)}.Concat(DebugAddMoreCharacters().Take(3)).ToArray()         ,
         // 参数2          charas =>          {            allies = charas;            battleSummonManager = new BattleSummonManager(summon);            battleSummonManager.SetAllies(charas);            battleFightManager.BeginBattle(battleSummonManager, new CharacterSelector(cameraFollowManager, enemies));          }      );     yield return charactersLoading; }   private IEnumerable<CharacterCreationInfo> DebugAddMoreCharacters(){        yield return new CharacterCreationInfo(CharacterType.Helper, CharacterClass.Warrior);        yield return new CharacterCreationInfo(CharacterType.Beast, CharacterClass.Warrior);        yield return new CharacterCreationInfo(CharacterType.Beast, CharacterClass.Warrior);        yield return new CharacterCreationInfo(CharacterType.Beast, CharacterClass.Warrior);        yield break;        var availableCharacterClasses = Enum.GetValues(typeof(CharacterClass))            .Cast<CharacterClass>()            .Take(4)  // filter out the player characters            .Where(x => x != SceneManager.Instance.MyCharacterClass)            .ToArray();        yield return new CharacterCreationInfo(CharacterType.Helper, availableCharacterClasses[0]);}