yield in C#

澳贼

yield in C# 到底有啥好处？？ 那位大仙给举例说明一下？？？

http://msdn.microsoft.com/en-us/library/9k7k7cf0(v=vs.80).aspx

没看懂

http://www.ytechie.com/2009/02/u ... nd-performance.html

还是没看懂

coolioo

Simply put, yield is a syntax sugar

If you want to use foreach on a customise collection class/type, the class has to implement the IEnumerable interface.
IEnumerable interface has one method: GetEnumerator(), which return a IEnumerator (interface). You have to create a class that implement the IEnumerator interface, this class contains the logic for how to iterate through you collection type.

In C# 2.0, a new key word is introduced, “yield return”. It is a syntax sugar which helps you quickly create a iterator method returns a Enumerator. If compiler sees “yield return” in a method, it will know that this isn’t a normal method but one implemented with an iterator block. Then compiler will automatically generate a Enumerator class using the logic. Normally “yield return” is used in the GetEnumerator() method when implementing IEnumerable interface to reduce code. By doing this, you dont need to create another class implement the IEnumerator interface, compiler will do this for you using the logic in the “yield return” method.

You can only use “yield return” in iterator blocks to implement methods that have a return type of IEnumerable, IEnumerator, or one of the generic equivalents.

[ 本帖最后由 coolioo 于 2011-2-3 15:58 编辑 ]

澳贼

原帖由 coolioo 于 2011-2-3 15:57 发表
Simply put, yield is a syntax sugar

If you want to use foreach on a customise collection class/type, the class has to implement the IEnumerable interface.
IEnumerable interface has one method: GetEnu ...

还是不太懂

coolioo

不懂是正常的，C#2.0，3.0增加了很多新的keyword，其实没什么大用，都是Syntax Sugar，就是让你少写几行代码而已。其实这样的代码读起来更费劲。

uowzd01

没用过

coolioo

yield return主要的作用是简化实现IEnumerable interface的代码

先读这个代码，http://msdn.microsoft.com/en-us/ ... 1%28v=VS.80%29.aspx
People是一个自定义类，为了在foreach中使用People，People必须实现IEnumerable接口。为了实现IEnumerable接口，必须再定义一个新类PeopleEnum来实现IEnumerator接口。

如果用yield return，你就不必定义PeopleEnum类，是代码长度大大缩小。

1.     public class PeopleNew : IEnumerable
   
2.     {
   
3.         private Person[] _people;
   
4.         public PeopleNew(Person[] pArray)
   
5.         {
   
6.             _people = new Person[pArray.Length];
   
7. 
   
8.             for (int i = 0; i < pArray.Length; i++)
   
9.             {
   
10.                 _people[i] = pArray[i];
    
11.             }
    
12.         }
    
13. 
    
14.         public IEnumerator GetEnumerator()
    
15.         {
    
16.             for (int i = 0; i < _people.Length; i++)
    
17.             {
    
18.                 yield return _people[i];
    
19.             }
    
20.         }
    
21.     }

复制代码

[ 本帖最后由 coolioo 于 2011-2-3 16:59 编辑 ]

dalaohu

Without yield, u need to manually add items to collection.

Its a code saver

With one small restriction

Only return ienumerable<t>

wp7 keyboard rox

With one small restriction

Only English...

coolioo

Only return ienumerable<t>

what does this mean??