IEnumerable.Select和SelectMany的区别
IEnumerable<T>在Windows Phone 7的程序上很常用，它允许开发人员定义foreach语句功能的实现并支持非泛型方法的简单迭代，下面主要分析一下 IEnumerable<T>.Select和IEnumerable<T>.SelectMany这两个方法的区别。
IEnumerable<T>.Select 将序列中的每个元素投影到新表中。
IEnumerable<T>.SelectMany 将序列的每个元素投影到 IEnumerable<T> 并将结果序列合并为一个序列。
SelectMany 方法枚举输入序列，使用转换函数将每个元素映射到 IEnumerable<T>，然后枚举并生成每个这种 IEnumerable<T> 对象的元素。 也就是说，对于 source 的每个元素，selector 被调用，返回一个值的序列。 然后 SelectMany将集合的此二维集合合并为一维 IEnumerable<T> 并将其返回。
下面一个小例子用IEnumerable<T>.Select和IEnumerable<T>.SelectMany实现同样的功能，看看两者的区别。
<
Grid
x:Name
="ContentPanel"
Grid.Row
="1"
Margin
="12,0,12,0"
>
<
ListBox
Name
="Output"
HorizontalAlignment
="Stretch"
VerticalAlignment
="Stretch"
Margin
="10"
/>
<
ListBox
Name
="Output2"
HorizontalAlignment
="Stretch"
VerticalAlignment
="Stretch"
Margin
="200,10,10,10"
/>
</
Grid
>
cs页面
namespace
LinqApplication {
public
partial
class
MainPage : PhoneApplicationPage { List
<
Book
>
Books;
//
List<T>继承了IEnumerable<T> 接口
public
MainPage() { InitializeComponent(); CreateBooks();
//
IEnumerable<Book>.Select 将序列中的Authors元素投影到新表中。
IEnumerable
<
List
<
Author
>>
EnumerableOfListOfAuthors
=
Books.Select(book
=>
book.Authors);
foreach
(var listOfAuthors
in
EnumerableOfListOfAuthors) {
foreach
(Author auth
in
listOfAuthors) { Output.Items.Add(auth.Name);
//
添加到ListBox里面
} }
//
IEnumerable<Book>.SelectMany 将序列的每个元素投影到 IEnumerable<T> 并将结果序列合并为一个序列。
IEnumerable
<
Author
>
authors
=
Books.SelectMany(book
=>
book.Authors);
foreach
(Author auth
in
authors) { Output2.Items.Add(auth.Name); } }
private
void
CreateBooks() { Books
=
new
List
<
Book
>
(); Author auth1
=
new
Author() { Name
=
"
张三
"
, Age
=
32
}; Author auth2
=
new
Author() { Name
=
"
李四
"
, Age
=
30
}; Author auth3
=
new
Author() { Name
=
"
加菲猫
"
, Age
=
31
}; List
<
Author
>
authors
=
new
List
<
Author
>
() { auth1, auth2, auth3 }; Book newBook
=
new
Book() { Authors
=
authors, NumPages
=
500
, Title
=
"
Programming C#
"
}; Books.Add(newBook); auth1
=
new
Author() { Name
=
"
刘德华
"
, Age
=
42
}; authors
=
new
List
<
Author
>
() { auth1 }; newBook
=
new
Book() { Authors
=
authors, NumPages
=
350
, Title
=
"
Book 2
"
}; Books.Add(newBook); auth1
=
new
Author() { Name
=
"
周杰伦
"
, Age
=
32
}; auth2
=
new
Author() { Name
=
"
林志玲
"
, Age
=
32
}; authors
=
new
List
<
Author
>
() { auth1, auth2 }; newBook
=
new
Book() { Authors
=
authors, NumPages
=
375
, Title
=
"
Programming with WP7
"
}; Books.Add(newBook); } } }
Author.cs类
namespace
LinqApplication {
public
class
Author {
public
string
Name;
public
int
Age; } }
Book.cs类
namespace
LinqApplication {
public
class
Book {
public
String Title {
get
;
set
; }
public
List
<
Author
>
Authors {
get
;
set
; }
public
int
NumPages {
get
;
set
; } } }