Best way to handle a KeyNotFoundException

phsr_53587 0
Viewed 85657

I am using a dictionary to perform lookups for a program I am working on. I run a bunch of keys through the dictionary, and I expect some keys to not have a value. I catch the KeyNotFoundException right where it occurs, and absorb it. All other exceptions will propagate to the top. Is this the best way to handle this? Or should I use a different lookup? The dictionary uses an int as its key, and a custom class as its value.

keynotfoundexception exception c#
6 Answers

Use Dictionary.TryGetValue instead:

Dictionary<int,string> dictionary = new Dictionary<int,string>();
int key = 0;
dictionary[key] = "Yes";

string value;
if (dictionary.TryGetValue(key, out value))
{
    Console.WriteLine("Fetched value: {0}", value);
}
else
{
    Console.WriteLine("No such key: {0}", key);
}
user_226560

Try using: Dict.ContainsKey

Edit:
Performance wise i think Dictionary.TryGetValue is better as some other suggested but i don't like to use Out when i don't have to so in my opinion ContainsKey is more readable but requires more lines of code if you need the value also.

Petoj_585530

you should use the 'ContainsKey(string key)' method of the Dictionary to check if a key exists. using exceptions for normal program flow is not considered a good practice.

Remco_Ros_703150

I know this is an old thread but in case it's helpful the prior answers are great, but the comments of complexity and concerns of littering the code (all valid for me also) can be addressed.

I use a custom extension method to wrap up the complexity of the above answers in a more elegant form so that it's not littered throughout the code, and it then enables great support for null coalesce operator . . . while also maximizing performance (via above answers).

namespace System.Collections.Generic.CustomExtensions
{
    public static class DictionaryCustomExtensions
    {
        public static TValue GetValueSafely<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key)
        {
            TValue value = default(TValue);
            dictionary.TryGetValue(key, out value);
            return value;
        }
    }
}

Then you can use it simply by importing the namespace System.Collections.Generic.CustomExtensions

string value = dictionary.GetValueSafely(key) ?? "default";
user_72931420
Related