一直听说foreach会有gc产生，有说.net3.5之前有，.net4则修复，一直没有测试，今天测试记录一下

测试在Update中进行：

1. foreach遍历字典有GC，不过只有第一次有。例如：在update中，两句代码都用foreach遍历同一个字典，则只有第一个foreach有gc产生。

//第一种方法
foreach (var item in peopleDictionary)
{
}
//第二种方法
foreach (KeyValuePair keyValuePair in peopleDictionary)
{}

2. for循环遍历字典，同样的，如果两句代码遍历同一个字典。也只有第一次有GC产生。可以使用下面代码。

IEnumerator ee = peopleDictionary.GetEnumerator();
ee.MoveNext();
for (int i = 0; i < peopleDictionary.Count; ee.MoveNext(), i++)
{
}

3. 使用foreach循环遍历其中的key或values，则会分别产生额外GC，同样只只产生一次。如下面代码

foreach (var item in peopleDictionary.Values)
{
}
foreach (var item in peopleDictionary.Keys)
{
}

4. 再来一个，每帧都有GC产生的方法，哈哈。

//每帧都有GC产生
IEnumerator ee = peopleDictionary.GetEnumerator();
ee.MoveNext();
for (int i = 0; i < peopleDictionary.Count; ee.MoveNext(), i++)
{
}
//只有一次有GC产生，关键字var
var ee = peopleDictionary.GetEnumerator();
ee.MoveNext();
for (int i = 0; i < peopleDictionary.Count; ee.MoveNext(), i++)
{
}

5. GC产生的大小，与字典存的数据结构有关，存int的GC 就小于存Class GC。

总结：

1. 遍历List、Array。for循环、 foreach循环、while循环都没有GC。

2. 遍历Dictionary。for循环、 foreach循环，第一次都会产生GC。只有一次也可以放心使用。

最后来一段测试代码，大家可以自行测试

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEngine.Profiling;
//using System.Collections.Specialized;public class People
{public string Name;public int Age;
}public class Test : MonoBehaviour
{int[] tempsInts = new[] { 1, 3, 4, 5, 6 };private People[] peoples;private List peoplesList;private List intList;private Dictionary peopleDictionary;private Dictionary intDictionary;private int tem;// Use this for initializationvoid Awake(){peoples = new People[5];peoplesList = new List();intList = new List();peopleDictionary = new Dictionary();intDictionary = new Dictionary();for (int i = 0; i < 5; i++){People people = new People();people.Age = i;people.Name = ((char)'A' + i).ToString();peoples[i] = people;peoplesList.Add(people);peopleDictionary.Add(i, people);intDictionary.Add(i, i);intList.Add(i);}}void Update(){Profiler.BeginSample("Foreach Int Dictionary  PeoplePeoplePeople");foreach (KeyValuePair keyValuePair in peopleDictionary){}Profiler.EndSample();Profiler.BeginSample("Foreach Int Dictionary-2-2-2");foreach (KeyValuePair keyValuePair in peopleDictionary){}Profiler.EndSample();Profiler.BeginSample("Foreach Int Dictionary-5-5-5");foreach (var item in peopleDictionary){}Profiler.EndSample();Profiler.BeginSample("For Int Dictionary1111----");var e = peopleDictionary.GetEnumerator();e.MoveNext();for (int i = 0; i < peopleDictionary.Count; e.MoveNext(), i++){}Profiler.EndSample();Profiler.BeginSample("For Int Dictionary2222----");IEnumerator ee = peopleDictionary.GetEnumerator();ee.MoveNext();for (int i = 0; i < peopleDictionary.Count; ee.MoveNext(), i++){}Profiler.EndSample();Profiler.BeginSample("Foreach Int Dictionary-1-1-1");foreach (var item in peopleDictionary.Keys){}Profiler.EndSample();Profiler.BeginSample("Foreach Int Dictionary000----");foreach (var item in peopleDictionary.Values){}Profiler.EndSample();Profiler.BeginSample("Foreach Int Dictionary999----");foreach (People item in peopleDictionary.Values){}Profiler.EndSample();}
}