这个词典如何？TKey，TValue>例外可能吗 [英] How is this Dictionary<TKey, TValue> exception possible?

问题描述

给定以下堆栈跟踪：

MESSAGE: Value cannot be null.Parameter name: key  
SOURCE: mscorlib  
TARGETSITE: Void ThrowArgumentNullException(System.ExceptionArgument)  
STACKTRACE:  
   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)  
   at System.Collections.Generic.Dictionary'2.FindEntry(TKey key)  
   at System.Collections.Generic.Dictionary'2.get_Item(TKey key)  
   at MyCompany.MAF.Agent.ServiceContracts.ConvertUtils.Convert(Dictionary'2 from) in D:\Development\MAF\Agent\MyCompany.MAF.Agent\ServiceContracts\ConvertUtils.cs:line 11

我得出以下结论：以下代码块从输入Dictionary的Keys集合中检索到一个null。但是，输入字典是 Dictionary< string，string> 的实例。 Dictionary < ; 使得条件不可能。在添加具有空键的项目时，会抛出异常。

I conclude that somehow the following block of code has retrieved a null from the input Dictionary's Keys collection. However, the input dictionary is an instance of Dictionary<string, string>. The implementation of Dictionary<string, string> makes that condition impossible. Upon adding an item with a null key, an exception is thrown.

internal static KeyValuePair<string, string>[] Convert(IDictionary<string, string> from)
{
    List<KeyValuePair<string, string>> ret = new List<KeyValuePair<string, string>>();
    foreach (string key in from.Keys)
        ret.Add(new KeyValuePair<string, string>(key, from[key]));
    return ret.ToArray();
}

推荐答案

我遇到过这个问题经常发生，因为我犯了允许多个线程访问同一个字典的错误。确保不是这种情况，因为字典不是线程安全的。

I've had this problem happen frequently because I made the mistake of allowing multiple threads to access the same dictionary. Make sure that this is not the case, because Dictionary is not thread-safe.

（顺便说一句，你的方法可以大大简化字典< K，V> 已经是一个 IEnumerable< KeyValuePair< K，V> 您应该可以在 ToArray 之间。

(Incidentally, your method can be greatly simplified. Dictionary<K,V> is already an IEnumerable<KeyValuePair<K,V>>. You should be able to just do ToArray on one.

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