I have a dictionary of objects. Then I created an empty List as an element of that dictionary.

Dictionary<string, object> mydictionary = new Dictionary<string, object>();
mydictionary["names"] = new List<string>();

Then I try to add a name into the List, but couldn't.

mydictionary["names"].Add("Jack"); -> ERROR "object does not contain definition of Add"

How can I add values to this List?
Note: I can't change the dictionary type. It must be <string,object>.

CodePudding user response：

The compiler only knows that the entries are of type object, at compile time it doesnt know that this object is one that supports Add. I mean what Add would that be? You could also have a BigInteger object and a database. SO the compiler doesnt know how to do

mydictionary["name"].Add()

because it doesn't know what Add to call, or even if the object has an Add. This is because c# is a statically typed language. You need to tell the compiler what the object is

((List<string>)mydictionary["name"]).Add()

ie cast the object to the right type.

CodePudding user response：

You have to specifically mention the type of value, like

((IList<string>) mydictionary["names"]).Add("Jack");

or you can use as

(mydictionary["names"] as (IList<string>)).Add("Jack");

Why?

• Because you declared dictionary as a <string, object>.
• When you added key-value pair i.e. mydictionary["names"] = new List<string>();, the value get stored as an object not a List.
• This is the reason when you are trying to add any string to a list, dictionary value is not recognized as a list,
• We fixed this problem, by type-casting an object to a list.