C＃Collection被修改了;

C# Collection was modified; enumeration operation may not execute

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Collection was modified; enumeration operation may not execute

你好，

我正在创建一个项目估算程序，并收到以下错误：C集合已修改；枚举操作可能无法执行。

与使用此相关：我在全球范围内通过以下方式初步宣布该裁决：

1	Dictionary<int, int> rankings = new Dictionary<int, int>();

包含此字典的下一个方法执行以下操作：

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private void getFirstEstimation()
{
List<int> array = new List<int>();

string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
MySqlConnection connection = new MySqlConnection(strConnection);
MySqlCommand command = connection.CreateCommand();
MySqlDataReader reader;
command.CommandText ="SELECT idprojects FROM `test`.`projects` WHERE application_layers =" + applicationTiers;
connection.Open();

reader = command.ExecuteReader();
while (reader.Read())
{
array.Add(Convert.ToInt32(reader["idprojects"].ToString()));
}
foreach (int i in array)
{
rankings[i] = 15;
}
connection.Close();
}

我在这里第二次这么叫：

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private void getSecondEstimation()
{
Dictionary<int, string> sqltext = new Dictionary<int, string>();
Dictionary<int, int> valueForSql = new Dictionary<int, int>();
Dictionary<int, int> weightings = new Dictionary<int, int>();
sqltext.Add(1,"project_type");
valueForSql.Add(1, projectType);
weightings.Add(1, 10);
sqltext.Add(2,"application_domain");
valueForSql.Add(2, applicationDomain);
weightings.Add(2, 8);
sqltext.Add(3,"organisation_size");
valueForSql.Add(3, organizationSize);
weightings.Add(3, 8);
sqltext.Add(4,"no_of_locations");
valueForSql.Add(4, noOfLocations);
weightings.Add(4, 7);
sqltext.Add(5,"development_process");
valueForSql.Add(5, developmentProcess);
weightings.Add(5, 6);
sqltext.Add(6,"rules_engine");
valueForSql.Add(6, rulesEngine);
weightings.Add(6, 5);
sqltext.Add(7,"middleware");
valueForSql.Add(7, middleware);
weightings.Add(7, 4);
sqltext.Add(8,"location_of_development");
valueForSql.Add(8, locationOfDevelopment);
weightings.Add(8, 3);
sqltext.Add(9,"programming_language");
valueForSql.Add(9, programmingLanguage);
weightings.Add(9, 3);
sqltext.Add(10,"development_environment");
valueForSql.Add(10, developmentEnvironment);
weightings.Add(10, 3);
sqltext.Add(11,"backend");
valueForSql.Add(11, backend);
weightings.Add(11, 3);
sqltext.Add(12,"webserver");
valueForSql.Add(12, webServer);
weightings.Add(12, 3);

List<int> array = new List<int>();

string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
MySqlConnection connection = new MySqlConnection(strConnection);
MySqlCommand command = connection.CreateCommand();
MySqlDataReader reader;

for (int i = 1; i <= 12; i++)
{
command.CommandText ="SELECT idprojects FROM `test`.`projects` WHERE" + sqltext[i] +" =" + valueForSql[i];
connection.Open();
//int testInt;
reader = command.ExecuteReader();
while (reader.Read())
{
array.Add(Convert.ToInt32(reader["idprojects"].ToString()));
}
foreach (int a in array)
{
if (!rankings.ContainsKey(a))
{
rankings[a] = 0;
}
rankings[a] = rankings[a] + weightings[i];
}
connection.Close();
}
}

问题出现在代码的这个区域：

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private void getThirdEstimation()
{
ArrayList tempModuleHolder;

string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
MySqlConnection connection = new MySqlConnection(strConnection);
MySqlCommand command = connection.CreateCommand();
MySqlDataReader reader;
int similarModules;

foreach (KeyValuePair<int, int> kvp in rankings)
{
similarModules = 0;
tempModuleHolder = new ArrayList();
command.CommandText ="SELECT id_modules FROM `test`.`modules_in_project` WHERE id_project =" + kvp.Key;
connection.Open();

reader = command.ExecuteReader();
while (reader.Read())
{
tempModuleHolder.Add(Convert.ToInt32(reader["id_modules"].ToString()));
}

foreach (int i in tempModuleHolder)
{
if(modules.Contains(i))
{
similarModules++;
}
}
if((double)(similarModules/modules.Count)>0.6)
{
//kvp.Value = kvp.Value + 4;
rankings[kvp.Key] = rankings[kvp.Key] + 4;
}
connection.Close();
}
}

如果有任何帮助解决问题，我们将不胜感激。

相关讨论

该错误确切地告诉您问题是什么(在调试器中运行或读取堆栈跟踪将确切地告诉您问题在哪里)：

C# Collection was modified; enumeration operation may not execute.

你的问题是循环

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foreach (KeyValuePair<int, int> kvp in rankings) {
//
}

其中修改了集合rankings。特别是进攻线是

1	rankings[kvp.Key] = rankings[kvp.Key] + 4;

在进入循环之前，请添加以下行：

1	var listOfRankingsToModify = new List<int>();

将违规行替换为

1	listOfRankingsToModify.Add(kvp.Key);

在你退出循环之后

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foreach(var key in listOfRankingsToModify) {
rankings[key] = rankings[key] + 4;
}

也就是说，记录需要进行的更改，并在不迭代需要修改的集合的情况下进行更改。

正如其他人指出的，您正在修改一个正在迭代的集合，这就是导致错误的原因。违规代码如下：

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foreach (KeyValuePair<int, int> kvp in rankings)
{
.....

if((double)(similarModules/modules.Count)>0.6)
{
rankings[kvp.Key] = rankings[kvp.Key] + 4; // <--- This line is the problem
}
.....

上面代码中不明显的是Enumerator的来源。在几年前关于EricLippert的一篇博客文章中，提供了一个示例，说明编译器将foreach循环扩展到了什么程度。生成的代码如下所示：

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{
IEnumerator<int> e = ((IEnumerable<int>)values).GetEnumerator(); // <-- This
// is where the Enumerator
// comes from.
try
{
int m; // OUTSIDE THE ACTUAL LOOP in C# 4 and before, inside the loop in 5
while(e.MoveNext())
{
// loop code goes here
}
}
finally
{
if (e != null) ((IDisposable)e).Dispose();
}
}

如果您在msdn文档中查找IEnumerable(这是GetEnumerator()返回的)，您将看到：

Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

这使我们回到错误消息的状态，而其他答案的状态，您正在修改基础集合。