How to use dictionaries with lists as value c# unity

When you declare such a dictionary its keys and values are empty.

Let’s say I create one such dictionary

var myDict = new Dictionary<string, List<string>>()

Now I want to add a value. But remember, my value is a List<T>.

So you need to check if your key is already present, and if it is already have an instanciated list as a value (e.g. a value != null)

if(myDict.ContainsKey("myKey") && myDict["myKey"] != null)
{
    // In this case you could do
    mydict["myKey"].Add("myValue");
    // Because you already have a list.
    // And to read the first item from the list
    var firstValue = mydict["myKey"][0]; // or using Linq replace [0] by First()
}

// Now if the key does not exist you need to add the key, and ideally an instantiated list.
if(!myDict.ContainsKey["myKey"])
{
    // In your case we know the expected length of the list, so let's specify it.
    myDict.Add("myKey", new List<string>(8))
}

You’ll notice I didn’t write the case where the key would exist, but the value is null.

I’ll leave to your consideration if handling that particular case is needed, and if it is, you should have all necessary information in the example above.