本篇简单回顾C#语言集合操作
变化
通过和Linq对等面向对象语法来认识Linq
Linq是Language Integrated Query
初识Linq感觉跟SQL ServerTsql很像可以进行语言必备逻辑操作也可以实现对集合直接查询Net1.X时代
C#不支持泛型
集合用元素只能为object类型ArrayList等添加、取出元素都和Object类型进行强制类型转换,
如果是值类型要进行装箱操作
取出元素时进行拆箱操作,影响效率编译时不进行类型检查
类型不匹配运行时可能出错定义实体类:
public 
Employee
{
private 
_Name;
private 
_Age;
private _Phone;
public Name
{
get { 
_Name; }
{ _Name = value; }
}
public Age
{
get { _Age; }
{ _Age = value; }
}
public Phone
{
get { _Phone; }
{ _Phone = value; }
}
public Employee( name, age, phone)
{
_Name = name;
_Age = age;
_Phone = phone;
}
}初识化集合:
这进行类型转换
ArrayList list;
list = 
ArrayList
;
list.Add( Employee("Zxjay", 20, "010-123456"));
list.Add( Employee("Andy", 30, "020-123456"));
list.Add( Employee("Bill", 50, "010-3456789"));
list.Add( Employee("Lee", 40, "0532-234567"));排序:
需实现IComparer接口
SortArrayList : IComparer
{
public Compare(object x, object y)
{
Employee a = x as Employee;
Employee b = y as Employee;
a.Name.CompareTo(b.Name);
}
}
list.Sort( SortArrayList);遍历每个元素取得符合条件
元素放到新集合:这里也进行类型转换
ArrayList selectedList = ArrayList;
foreach (object obj in list)
{
Employee emp = obj as Employee;
(emp != null && emp.Phone.StartsWith("010") && emp.Age < 50)
{
selectedList.Add(emp);
}
}输出集合元素:
这里也进行类型转换
private void ShowList(ArrayList list)
{
Console.WriteLine("{0,-20:G}{1,-5:G}{2}", "Name", "Age", "Phone");
foreach (object obj in list)
{
Employee emp = obj as Employee;
(emp != null)
{
Console.WriteLine("{0,-20:G}{1,-5:G}{2}", emp.Name, emp.Age, emp.Phone);
}
}
}.NET 2.0时代
加入了泛型和匿名思路方法
代码量减少逻辑清晰了许多编译期间强类型检查和去掉了强制类型转换及装箱、拆箱操作定义实体类跟.NET 1.1时代
样排序选择直接用匿名思路方法实现:
list.Sort(
delegate(Employee x, Employee y)
{
x.Name.CompareTo(y.Name);
}
);
List<Employee> listBeijing = list.FindAll(
delegate(Employee emp)
{
emp.Phone.StartsWith("010") && emp.Age < 50;
}
);输出集合元素:
这里去掉了强制类型转换
private void ShowList(IList<Employee> list)
{
Console.WriteLine("{0,-20:G}{1,-5:G}{2}", "Name", "Age", "Phone");
foreach (Employee emp in list)
{
Console.WriteLine("{0,-20:G}{1,-5:G}{2}", emp.Name, emp.Age, emp.Phone);
}
}.Net 3.X时代
自动属性、扩展思路方法、隐含类型、匿名类型、类型集合初识化器、Lambda表达式
有大大简化了编程复杂度定义实体类:
用自动属性
public Employee
{
public Name { get; ; }
public Age { get; ; }
public Phone { get; ; }
}
化集合:list = List<Employee>
{
Employee{ Name = "Zxjay", Age = 20, Phone = "010-123456" },
Employee{ Name = "Andy", Age = 30, Phone = "020-123456" },
Employee{ Name = "Bill", Age = 50, Phone = "010-345678" },
Employee{ Name = "Lee", Age = 40, Phone = "010-234567" }
};排序选择:
用Lambda表达式实现:
list.Sort((Employee x, Employee y) => { x.Name.CompareTo(y.Name); });
var listBijing = list.FindAll(
(Employee emp) => { emp.Phone.StartsWith("010") && emp.Age < 50; });输出集合元素:
用扩展思路方法
private void ShowList(List<Employee> list)
{
Console.WriteLine("{0,-20:G}{1,-5:G}{2}", "Name", "Age", "Phone");
list.ForEach((Employee emp) => Console.WriteLine("{0,-20:G}{1,-5:G}{2}", emp.Name, emp.Age, emp.Phone));
}这些查询大大简化
但这些还是面向对象思路方法Linq这样实现排序选择等操作:
var selectResult = from emp in list
where emp.Phone.StartsWith("010") && emp.Age < 50
orderby emp.Name
select emp;这才是真正意义上
语言集成查询是不是似曾相识？跟SQL语句相似只是把select字句放在最后本篇仅仅是对Linq
概述及语言内集合查询机制变化概要介绍Linq内容将在下面内容步步展开
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