c# - (有时)词典中不存在给定的键

Question

我正在使用下面的代码以list参数启动线程，但有时会引发异常:

The given key was not present in the dictionary

从这一行:

Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[i]));

我该如何解决该错误？

完整代码:

var ControllerDictionary = ConfigFile.ControllerList.Select((c, i) => new { Controller = c, Index = i })
    .GroupBy(x => x.Index % AppSettings.SimultaneousProcessNumber)
    .Select((g, i) => new { GroupIndex = i, Group = g })
    .ToDictionary(x => x.GroupIndex, x => x.Group.Select(xx => xx.Controller).ToList());

for (int i = 0; i < ControllerDictionary.Count; i++)
{
     Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[i]));
     MoveThread.Start();

     foreach (var Controller in ControllerDictionary[i])
         Logger.Write(string.Format("{0} is in move thread {1}.", Controller.Ip, (i + 1)),EventLogEntryType.Information, AppSettings.LogInfoMessages);
}

Answer 1

您正在捕获的是i变量，而不是其值。因此，当前您可能有多个线程使用相同的索引调用MoveTask ...有时i的值可能等于ControllerDictionary.Count。

如果将i的副本复制到循环中的变量中，则会解决此问题，因为在循环的每次迭代中都会得到一个单独的变量:

for (int i = 0; i < ControllerDictionary.Count; i++)
{
    int index = i;
    Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[index]));
    ... 
}

甚至更好的是，从线程中完全提取 ControllerDictionary提取:

for (int i = 0; i < ControllerDictionary.Count; i++)
{
    var value = ControllerDictionary[i];
    Thread MoveThread = new Thread(() => MoveTask(value));
    ... 
}

此外，目前还不清楚为什么要使用字典。既然您知道键都在 [0, count)范围内，为什么不只使用数组呢？您可以将查询更改为:

var controllerLists = ConfigFile.ControllerList
    .Select((c, i) => new { Controller = c, Index = i })
    .GroupBy(x => x.Index % AppSettings.SimultaneousProcessNumber)
    .Select(g => g.Select(xx => xx.Controller).ToList())
    .ToArray();