Not able to use GetValueOrDefault() for Dictionary in C#

user_6155965 0
Viewed 12035

I've defined a Dictionary with some custom type like this,

 public readonly Dictionary<PricingSection, View> _viewMappings = new Dictionary<PricingSection, View>();

Now when i try to do 

_viewMappings.GetValueOrDefault(section);

section is of type PricingSection

i'm getting an error saying

Severity Code Description Project File Line Suppression State Error CS1061 'Dictionary' does not contain a definition for 'GetValueOrDefault' and no accessible extension method 'GetValueOrDefault' accepting a first argument of type 'Dictionary' could be found (are you missing a using directive or an assembly reference?)

Am i missing something ??

.net-standard xamarin.forms dictionary c#
4 Answers

Am i missing something ??

You are missing the fact Dictionary does not contain any method of this name GetValueOrDefault

Dictionary<TKey,TValue> Class

Maybe you are looking for

Dictionary<TKey,TValue>.TryGetValue(TKey, TValue) Method

Gets the value associated with the specified key.

or

ImmutableDictionary.GetValueOrDefault<TKey, TValue> Method (IImmutableDictionary<TKey, TValue>, TKey)

Gets the value for a given key if a matching key exists in the dictionary.

You could however implement your own

public static class Extensions
{
    public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict,TKey key)
      =>  dict.TryGetValue(key, out var value) ? value : default(TValue);
}

If you are using any of the following, there are extension method overloads for IReadOnlyDictionary

  • NET 5.0 RC1

  • .NET Core 3.1 3.0 2.2 2.1 2.0

  • .NET Standard 2.1

CollectionExtensions.GetValueOrDefault

Tries to get the value associated with the specified key in the dictionary

user_16129750

GetValueOrDefault() is part of ImmutableDictionary. so of course you get the error message. instead use

Dictionary.TryGetValue(TKey, TValue)

user_45276280

I use it in .Net Core (3.1)

class Dictionary<TKey, TValue> implements IReadOnlyCollection<KeyValuePair<TKey, TValue>>.

and there is and extension method in namespace System.Collections.Genericfor for IReadOnlyDictionary:

public static class CollectionExtensions
{
     ...
     public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key) where TKey : notnull;
     ...
}

so we get it out of the box also for Dictionary<TKey, TValue>.

(Not sure about .net framework which going to be obsolete anyway)

user_15440540

When I encountered the same problem, I was just missing this:

using System.Collections.Generic

As mentioned by @guyarad, this is an extension method on IReadOnlyDictionary but it needs to be imported. It seems obvious, but since you can use a returned dictionary without the import, it can be confusing when it mostly works but is missing some functionality you're pretty sure it should have.

user_27151070
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