通过示例演示捕获的工作方式可能是最简单的…
这是一些使用lambda表达式捕获单个变量的代码：
using System;
class Test
{
static void Main()
{
Action action = CreateShowAndIncrementAction();
action();
action();
}
static Action CreateShowAndIncrementAction()
{
Random rng = new Random();
int counter = rng.Next(10);
Console.WriteLine("Initial value for counter: {0}", counter);
return () =>
{
Console.WriteLine(counter);
counter++;
};
}
}
现在，这就是编译器为您执行的操作-只是它将使用“无法说”的名称，而这在C＃中是不可能真正出现的。
using System;
class Test
{
static void Main()
{
Action action = CreateShowAndIncrementAction();
action();
action();
}
static Action CreateShowAndIncrementAction()
{
ActionHelper helper = new ActionHelper();
Random rng = new Random();
helper.counter = rng.Next(10);
Console.WriteLine("Initial value for counter: {0}", helper.counter);
// Converts method group to a delegate, whose target will be a
// reference to the instance of ActionHelper
return helper.DoAction;
}
class ActionHelper
{
// Just for simplicity, make it public. I don't kNow if the
// C# compiler really does.
public int counter;
public void DoAction()
{
Console.WriteLine(counter);
counter++;
}
}
}
如果捕获在循环中声明的变量，那么ActionHelper对于循环的每次迭代，您都会得到一个新的实例-这样您就可以有效地捕获变量的不同“实例”。
当您捕获来自不同作用域的变量时，它会变得更加复杂…让我知道您是否真的想要那种详细程度，或者您可以编写一些代码，在Reflector中反编译然后按照以下步骤进行:)
注意如何：
编辑：这是两个代表共享变量的示例。一个代表显示的当前值counter，另一个代表增加它的值：
using System;
class Program
{
static void Main(string[] args)
{
var tuple = CreateShowAndIncrementActions();
var show = tuple.Item1;
var increment = tuple.Item2;
show(); // Prints 0
show(); // Still prints 0
increment();
show(); // Now prints 1
}
static Tuple<Action, Action> CreateShowAndIncrementActions()
{
int counter = 0;
Action show = () => { Console.WriteLine(counter); };
Action increment = () => { counter++; };
return Tuple.Create(show, increment);
}
}
…以及扩展：
using System;
class Program
{
static void Main(string[] args)
{
var tuple = CreateShowAndIncrementActions();
var show = tuple.Item1;
var increment = tuple.Item2;
show(); // Prints 0
show(); // Still prints 0
increment();
show(); // Now prints 1
}
static Tuple<Action, Action> CreateShowAndIncrementActions()
{
ActionHelper helper = new ActionHelper();
helper.counter = 0;
Action show = helper.Show;
Action increment = helper.Increment;
return Tuple.Create(show, increment);
}
class ActionHelper
{
public int counter;
public void Show()
{
Console.WriteLine(counter);
}
public void Increment()
{
counter++;
}
}
}
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