/**////////////////////////////////////////////
/Take,Skip,TakeWhile,SkipWhile的例子和解释//
/**///////////////////////////////////////////
class Program
{
DB#region DB
private static List<Student> GetStudents()
{
List<Student> students = new List<Student> {
new Student{ Name="YOUNG", Age=25, Language="Chinese"},
new Student{ Name="JESSIE", Age=21, Language="Scotland"},
new Student{ Name="KELLY", Age=18, Language="English"},
new Student{ Name="JUNE", Age=20, Language="Chinese"},
new Student{ Name="ADRIAN", Age=22, Language="Italy"},
new Student{ Name="BRUCE", Age=17, Language="Scotland"},
new Student{ Name="BRANT", Age=30, Language="Germany"},
new Student{ Name="BEN", Age=25, Language="Chinese"}
};
return students;
}
#endregion
static void Main(string[] args)
{
List<Student> studentList = GetStudents();
//Take(studentList);
//Skip(studentList);
}
Take#region Take
public static void Take<T>(T obj)
{
//GetElementFromCollect();
//GetElementFromSelectResult(obj);
//GetPointElement(obj);
//ForExampleAboutTakeWhileOrSkipWhile(obj);
}
private static void GetElementFromCollect()
{
Console.WriteLine("<hr>从集合中取固定数量的元素：<br>");
string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" };
//Take将枚举出source中的前count个元素,返回给客户端.
//Lambda的写法
//var books = stringArray.Take(3);
//Linq的写法
var books = (from n in stringArray
select n).Take(3);
foreach (var book in books)
{
Console.WriteLine(string.Format("<div class='result'>{0}</div>", book));
}
//扩展方法写法
//IEnumerator<String> stu_Lambda = stringArray.Take(3).GetEnumerator();
//while (stu_Lambda.MoveNext())
//{
// Console.WriteLine(stu_Lambda.Current);
//}
}
private static void GetElementFromSelectResult<T>(T obj)
{
Console.WriteLine("<hr>从select结果中取固定数量的元素：<br>");
//Lambda写法
//var stu = (RevealChangeType(obj).Where(n=>n.Language == "Chinese").Select(n=>new { n.Name, n.Age })).Take(1);
//Linq写法
var stu = (from n in RevealChangeType(obj)
where n.Language == "Chinese"
select new {n.Name, n.Age}).Take(1);
foreach (var student in stu)
{
Console.WriteLine(string.Format("<div class='result'> name:{0}; age:{1}</div>", student.Name, student.Age));
}
//扩展方法写法
//IEnumerator<Student> stu_ExtraMethod = RevealChangeType(obj).Where(n=>n.Language == "Chinese").Take(1).GetEnumerator();
//while (stu_ExtraMethod.MoveNext())
//{
// Console.WriteLine(stu_ExtraMethod.Current.Age);
//}
}
private static void GetPointElement<T>(T obj)
{
Console.WriteLine("<hr>取满足指定条件元素：<br>");
//Lambda写法
//var stu = RevealChangeType(obj).TakeWhile(student => student.Age > 20);
//Linq写法
var stu = (from n in RevealChangeType(obj)
select n).TakeWhile(n => n.Age > 20);
foreach (var student in stu)
{
Console.WriteLine(string.Format("<div class='result'>{0}</div>", student.Name));
}
//扩展方法写法
//IEnumerator<Student> stu_ExtraMethod = RevealChangeType(obj).TakeWhile(student => student.Age > 20).GetEnumerator();
//while (stu_ExtraMethod.MoveNext())
//{
// Console.WriteLine(stu_ExtraMethod.Current.Name);
//}
//TakeWhile在LINQ中实现的思想是:
//对数据源进行枚举,从第一个枚举得到的元素开始-->
// 调用客户端传入的predicate( c.Name == ""woodyN")-->
// 如果这个predicate委托返回true的话,
// 则将该元素作为Current元素返回给客户端,并且,继续进行相同的枚举,判断操作.
// 但是,一旦predicate返回false的话,
// MoveNext()方法将会返回false,枚举就此打住,忽略剩下的所有元素.
//所以此方法出来的结果是：
//<div class='result'>YOUNG</div>
//<div class='result'>JESSIE</div>
//因为在KELLYAge=18不符合当前where条件,所以会这样。：）
}
#endregion
Skip#region Skip
private static void Skip<T>(T obj)
{
//GetRemnantElementAfterJumpCollect();
//GetRemnantElementAfterFilter(obj);
}
private static void GetRemnantElementAfterJumpCollect()
{
Console.WriteLine("<hr>跳过集合的几个元素后取剩余所有元素：<br>");
string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" };
//Skip则恰好相反,将跳过source中的前count个元素,枚举其余元素.
//Lambda写法
//var books1 = stringArray.Skip(3);
//Linq写法
var books1 = (from n in stringArray
select n).Skip(3);
foreach (var book in books1)
{
Console.WriteLine(string.Format("<div class='result'>{0}</div>", book));
}
//扩展方法写法
//IEnumerator<string> books1_ExtraMethod = stringArray.Skip(3).GetEnumerator();
//while (books1_ExtraMethod.MoveNext())
//{
// Console.WriteLine(books1_ExtraMethod.Current);
//}
}
private static void GetRemnantElementAfterFilter<T>(T obj)
{
Console.WriteLine("<hr>将满足指定条件元素过滤后选择剩余的所有元素：<br>");
//Lambda写法
//var stu = RevealChangeType(obj).SkipWhile(student => student.Age > 20);
//Linq写法
var stu = (from n in RevealChangeType(obj)
select n).SkipWhile(n => n.Age > 20);
foreach (var student in stu)
{
Console.WriteLine(string.Format("<div class='result'>{0}</div>", student.Name));
}
//扩展方法写法
//IEnumerator<Student> stu_ExtraMethod = RevealChangeType(obj).SkipWhile(student => student.Age > 20).GetEnumerator();
//while (stu_ExtraMethod.MoveNext())
//{
// Console.WriteLine(stu_ExtraMethod.Current);
//}
//类似的,SkipWhile也对数据源进行枚举,从第一个枚举得到的元素开始,
//调用客户端的predicate,如果返回true,则跳过该元素,继续进行枚举操作.
//但是,如果一旦predicate返回为false,则该元素以后的所有元素,都不会再调用predicate,
//而全部枚举给客户端.
//所以此方法出来的结果是：
//<div class='result'>KELLY</div>
//<div class='result'>JUNE</div>
//<div class='result'>ADRIAN</div>
//<div class='result'>BRUCE</div>
//<div class='result'>BRANT</div>
//<div class='result'>BEN</div>
//以上根据这个结果对于linq中TakeWhile,SkipWhile有点认识了。
//但是我还是建议实际使用时还是要小心使用。
}
#endregion
TakeWhile--SkipWhile#region TakeWhile--SkipWhile
private static void ForExampleAboutTakeWhileOrSkipWhile<T>(T obj)
{
var stu = RevealChangeType(obj).TakeWhile(student => student.Age > 20);
var stu1 = RevealChangeType(obj).TakeWhile(student => student.Age > 18);
var stu2 = RevealChangeType(obj).SkipWhile(student => student.Age > 20);
var stu3 = RevealChangeType(obj).SkipWhile(student => student.Age > 18);
foreach (var student in stu)
{
Console.WriteLine(string.Format("<div class='[TakeWhile(student => student.Age > 20)]result'>{0}</div>", student.Name));
}
foreach (var student in stu1)
{
Console.WriteLine(string.Format("<div class='[TakeWhile(student => student.Age > 18)]result'>{0}</div>", student.Name));
}
foreach (var student in stu2)
{
Console.WriteLine(string.Format("<div class='[SkipWhile(student => student.Age > 20)]result'>{0}</div>", student.Name));
}
foreach (var student in stu3)
{
Console.WriteLine(string.Format("<div class='[SkipWhile(student => student.Age > 18)]result'>{0}</div>", student.Name));
}
//Runtime Result
//<div class='[TakeWhile(student => student.Age > 20)]result'>YOUNG</div>
//<div class='[TakeWhile(student => student.Age > 20)]result'>JESSIE</div>
//<div class='[TakeWhile(student => student.Age > 18)]result'>YOUNG</div>
//<div class='[TakeWhile(student => student.Age > 18)]result'>JESSIE</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>KELLY</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>JUNE</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>ADRIAN</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>BRUCE</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>BRANT</div>
//<div class='[SkipWhile(student => student.Age > 20)]result'>BEN</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>KELLY</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>JUNE</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>ADRIAN</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>BRUCE</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>BRANT</div>
//<div class='[SkipWhile(student => student.Age > 18)]result'>BEN</div>
}
#endregion
}
sealed class Student
{
public int age;
public int Age
{
get { return age; }
set { age = value; }
}
private string name;
public string Name
{
get { return name; }
set { name = value; }
}
private string language;
public string Language
{
get { return language; }
set { language = value; }
}
}
