Unity3D中的C#匿名函数作用域 [英] C# Anonymous Function Scope in Unity3D

问题描述

在Unity3D中创建模拟项目时，我遇到了这种令人困惑的行为.

I came across this puzzling behavior while making a simulation project in Unity3D.

基本上，我正在使用要循环的变量在循环中创建匿名函数，并将所有这些函数添加到队列中进行处理.
Unity3D Monobehavior中奇怪的情况是它们仅在最后一个循环变量上被调用

Basically, I was creating anonymous functions in a loop using the variable being looped, and add all these functions to a queue for processing.
The curious case in Unity3D Monobehavior is that they are only called on the last looped variable.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System;
public class TestDist : MonoBehaviour {

    int counter = 0;

    // Use this for initialization
    void Start () {

        List<LOL> lols = new List<LOL>();
        lols.Add(new LOL(1));
        lols.Add(new LOL(2));
        lols.Add(new LOL(3));

        List<Func<int>> fs = new List<Func<int>>();
        foreach (LOL l in lols)
        {
            //****** Critical Section *********
            Func<int> func = () =>
            {
                Debug.Log(l.ID);   //Prints "3" 3 times instead of
                return 0;          // "1", "2", "3"
            };
            //****** Critical Section *********

            fs.Add(func);
        }
        foreach (Func<int> f in fs)
        {
            f();
        }
    }

    // Update is called once per frame
    void Update () {
    }
}

class LOL
{
    public long ID;
    public LOL(long id)
    {
        ID = id;
    }
}

该代码在普通的Visual Studio Console应用程序中运行良好，但在Unity3D上失败. (版本5.0)通过打印最后一个值("3")而不是1,2,3来打印3次.
我尝试了各种方法来绕过该方法，但以下方法却没有明显的原因起作用: 将关键部分"更改为以下块可以解决此问题:

The code works good in plain Visual Studio Console application, but fails on Unity3D. (Version 5.0) by printing the last value ("3") 3 times instead of 1,2,3.
I tried various methods to circumvent and the following worked for no apparent reason : Changing the Critical Section to the following block solves the issue:

LOL another = l;
Func<int> func = () =>
{
    Debug.Log(another.ID);
    return 0;
};

如果有人可以回答(Unity Bug Fix Team似乎不在乎)会很高兴

Will be delighted if someone can answer (Unity Bug Fix Team does not seem to care)

推荐答案

您正面临关闭问题.

查看此问题: C#中的"closures"是什么?

试试看.它只是一样，但不是完全一样，因为您在循环中声明了新" lol:

Try this instead. Its merely the same, but not completely since you declare a "new" lol in your loop :

for( int index = 0 ; index < lols.Count ; ++index )
{
    Lol l = lols[index];
    Func<int> func = () =>
    {
        Debug.Log(l.ID);
        return 0;
    };
    fs.Add(func);
}

如果它不起作用，请尝试:

If it does not work, try :

foreach (LOL l in lols)
{           
    fs.Add(GetFunction(l.ID));
}

// ...

private Func<int> GetFunction( int identifier)
{     
    Func<int> func = () =>
    {
        Debug.Log(identifier);
        return 0;
    };
    return func ;
}

我必须承认，我对关闭并不满意.

I does not feel comfortable with closure, I must admit.

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