在Dictionary ContainsKey检查中找不到ArgumentException

Question

I have code like this:

if (!likeDict.ContainsKey(s))
{
    likeDict.Add(s, s);
}

And I keep getting an error that an item with the same key has already been added. I thought ContainsKey is the check for this and that is where the error is occuriing, not at the add line. Am I misinterpreting ContainsKey?

Answer 1

It sounds like you are using the dictionary in a multithreaded scenario. If this is the case, you can switch to using ConcurrentDictionary<TKey, TValue> which provides the following TryAdd method:

bool added = likeDict.TryAdd(s, s);

If you are using this dictionary as a cache for equivalent objects, you could also use the GetOrAdd method:

var value = likeDict.GetOrAdd(s, s);
bool added = object.ReferenceEquals(value, s);

Answer 2

The error could happen if this is static/shared resource (as pointed in previous comments). In this case, apply lock statement.

Hope this will help. My best, AB