关于Task.StartNew(Action< Object&gt ;, Object)方法 [英] About the Task.StartNew(Action<Object>, Object) method

问题描述

我正在此页面上学习TPL，一个代码块使我非常困惑.

I'm learning the TPL on this page, and one code block confuses me a lot.

我正在阅读此页:任务并行(任务并行库)

在一节中，它说下面的代码是正确的解决方案，因为循环中的lambda每次迭代后都无法获得其值，而最终值却无法获得.因此，您应该将"i"包装在CustomData对象中.代码如下:

in one section, it said that the following code is the right solution because a lambda in a loop can't get the value as it mutates after each iteration, but the final value. So you should wrap the "i" in a CustomData object. The code is below:

class CustomData
{
   public long CreationTime;
   public int Name; 
   public int ThreadNum;
}

public class Example
{
   public static void Main()
   {
      // Create the task object by using an Action(Of Object) to pass in custom data 
      // to the Task constructor. This is useful when you need to capture outer variables 
      // from within a loop. 
      Task[] taskArray = new Task[10];
      for (int i = 0; i < taskArray.Length; i++)
      {
         taskArray[i] = Task.Factory.StartNew( (Object obj ) =>
            {
               CustomData data = obj as CustomData;
               if (data == null) 
                  return;

               data.ThreadNum = Thread.CurrentThread.ManagedThreadId;
               Console.WriteLine("Task #{0} created at {1} on thread #{2}.", data.Name, data.CreationTime, data.ThreadNum);
            },
            new CustomData()
            {
               Name = i,
               CreationTime = DateTime.Now.Ticks
            });
      }
      Task.WaitAll(taskArray);     
   }
}

代码相当简单易懂，但这是我的问题:

The code is rather straightforward and easy to understand but here comes my problem:

在Task.Factory.StartNew()方法中，作者使用其重载形式之一:

in the Task.Factory.StartNew() method, the author uses one of its overload form:

Task.StartNew(Action<Object>, Object)

我很想知道"obj"来自哪里?它如何具有3个属性:名称，CreationTime和ThreadNum.

I am so curious to know where does the "obj" come from? How does it have 3 properties: Name, CreationTime and ThreadNum.

我在MSDN上搜索时发现没有有用的详细信息，但这是:一个包含要由动作委托使用的数据的对象." MSDN 确实没有解释任何事物.

I searched over MSDN found no useful detail but this: "An object containing data to be used by the action delegate." MSDN It really doesn't explain anything.

有人可以解释吗?

推荐答案

下面是一个更简洁的示例，可能有助于对其进行解释.

Here is a more concise example which may help to explain it.

void StartNew(Action<object> action, object o) {
  action(o);
}

StartNew方法仅接受action委托，并通过传递o作为参数来调用它.传递给lambda的值就是在lambda之后传递给StartNew的值

The StartNew method just takes the action delegate and invokes it by passing o as the parameter. The value passed to the lambda is simply the value that is passed into StartNew after the lambda

// Prints "hello world"
StartNew(o => Console.WriteLine(o), "hello world");

在您概述第二个参数为

new CustomData() {Name = i, CreationTime = DateTime.Now.Ticks} 

这只是创建一个类型为CustomData的新对象，为其分配一些属性，并将其作为紧接在其之前定义的lambda的参数.最终它将成为lambda值obj

This just creates a new object of type CustomData, assigns it some properties and makes it the argument to the lambda defined immediately before it. It will eventually become the value obj in the lambda

这篇关于关于Task.StartNew(Action< Object&gt ;, Object)方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！