我们这里有一些代码(在VS2005和c# 2.0中)，以前的工程师用他们的方式使用列表。ForEach(delegate(item) {foo;});而不是foreach(item in list) {foo;};他们写的所有代码。例如，从dataReader读取行的代码块。

我还是不知道他们为什么要这么做。

list.ForEach()的缺点是:

It is more verbose in C# 2.0. However, in C# 3 onwards, you can use the "=>" syntax to make some nicely terse expressions. It is less familiar. People who have to maintain this code will wonder why you did it that way. It took me awhile to decide that there wasn't any reason, except maybe to make the writer seem clever (the quality of the rest of the code undermined that). It was also less readable, with the "})" at the end of the delegate code block. See also Bill Wagner's book "Effective C#: 50 Specific Ways to Improve Your C#" where he talks about why foreach is preferred to other loops like for or while loops - the main point is that you are letting the compiler decide the best way to construct the loop. If a future version of the compiler manages to use a faster technique, then you will get this for free by using foreach and rebuilding, rather than changing your code. a foreach(item in list) construct allows you to use break or continue if you need to exit the iteration or the loop. But you cannot alter the list inside a foreach loop.

看到这个名单我很惊讶。ForEach稍微快一点。但这可能不是贯穿始终的有效理由，那将是不成熟的优化。如果你的应用程序使用的是数据库或web服务，而不是循环控制，那么时间几乎总是会花在那里。你也用for循环测试过它吗?列表中。ForEach可以更快，因为在内部使用它，没有包装器的for循环甚至更快。

我不同意list.ForEach(委托)版本在任何重要方面都“更实用”。它确实将一个函数传递给另一个函数，但在结果或程序组织方面没有太大的区别。

我不认为每一项都是这样。“确切地说你想怎么做”- a for(int 1 = 0;I < count;i++)循环可以做到这一点，foreach循环将控制的选择留给编译器。

My feeling is, on a new project, to use foreach(item in list) for most loops in order to adhere to the common usage and for readability, and use list.Foreach() only for short blocks, when you can do something more elegantly or compactly with the C# 3 "=>" operator. In cases like that, there may already be a LINQ extension method that is more specific than ForEach(). See if Where(), Select(), Any(), All(), Max() or one of the many other LINQ methods doesn't already do what you want from the loop.

整个ForEach作用域(委托函数)被视为一行代码(调用该函数)，您不能设置断点或进入代码。如果发生未处理的异常，则标记整个块。

这两者之间有一个重要而有用的区别。

因为.ForEach使用for循环来迭代集合，这是有效的(编辑:在。net 4.5之前-实现改变了，它们都抛出):

someList.ForEach(x => { if(x.RemoveMe) someList.Remove(x); }); 

而foreach使用枚举数，因此这是无效的:

foreach(var item in someList)
  if(item.RemoveMe) someList.Remove(item);

不要复制这段代码到你的应用程序中!

这些示例并不是最佳实践，它们只是为了演示ForEach()和ForEach之间的区别。

在for循环中从列表中删除项可能会产生副作用。最常见的是在这个问题的评论中描述的。

通常，如果希望从列表中删除多个项，则需要将确定要删除哪些项与实际删除分开。它不能使您的代码保持紧凑，但它保证您不会遗漏任何项。

您展示的第二种方法使用扩展方法为列表中的每个元素执行委托方法。

这样，您就有了另一个委托(=方法)调用。

此外，还可以使用for循环迭代列表。

我们这里有一些代码(在VS2005和c# 2.0中)，以前的工程师用他们的方式使用列表。ForEach(delegate(item) {foo;});而不是foreach(item in list) {foo;};他们写的所有代码。例如，从dataReader读取行的代码块。

我还是不知道他们为什么要这么做。

list.ForEach()的缺点是:

It is more verbose in C# 2.0. However, in C# 3 onwards, you can use the "=>" syntax to make some nicely terse expressions. It is less familiar. People who have to maintain this code will wonder why you did it that way. It took me awhile to decide that there wasn't any reason, except maybe to make the writer seem clever (the quality of the rest of the code undermined that). It was also less readable, with the "})" at the end of the delegate code block. See also Bill Wagner's book "Effective C#: 50 Specific Ways to Improve Your C#" where he talks about why foreach is preferred to other loops like for or while loops - the main point is that you are letting the compiler decide the best way to construct the loop. If a future version of the compiler manages to use a faster technique, then you will get this for free by using foreach and rebuilding, rather than changing your code. a foreach(item in list) construct allows you to use break or continue if you need to exit the iteration or the loop. But you cannot alter the list inside a foreach loop.

看到这个名单我很惊讶。ForEach稍微快一点。但这可能不是贯穿始终的有效理由，那将是不成熟的优化。如果你的应用程序使用的是数据库或web服务，而不是循环控制，那么时间几乎总是会花在那里。你也用for循环测试过它吗?列表中。ForEach可以更快，因为在内部使用它，没有包装器的for循环甚至更快。

我不同意list.ForEach(委托)版本在任何重要方面都“更实用”。它确实将一个函数传递给另一个函数，但在结果或程序组织方面没有太大的区别。

我不认为每一项都是这样。“确切地说你想怎么做”- a for(int 1 = 0;I < count;i++)循环可以做到这一点，foreach循环将控制的选择留给编译器。

My feeling is, on a new project, to use foreach(item in list) for most loops in order to adhere to the common usage and for readability, and use list.Foreach() only for short blocks, when you can do something more elegantly or compactly with the C# 3 "=>" operator. In cases like that, there may already be a LINQ extension method that is more specific than ForEach(). See if Where(), Select(), Any(), All(), Max() or one of the many other LINQ methods doesn't already do what you want from the loop.

在幕后，匿名委托被转换为一个实际的方法，因此如果编译器没有选择内联函数，那么第二个选择可能会有一些开销。此外，匿名委托示例主体引用的任何局部变量在本质上都会发生变化，因为编译器会使用一些技巧来隐藏它被编译为新方法的事实。这里有更多关于c#如何做到这一点的信息:

http://blogs.msdn.com/oldnewthing/archive/2006/08/04/688527.aspx