从 Linq.Enumerable WhereListIterator 中抓取 Object

Question

im trying to grab a Object(Class) out of a List, depending on a matching string. Im using the.Where function for the list. I have tried replacing it with different casts, but it always throws a InvalidCastException. Has anyone a idea how to directly cast or get the object out of the list?

Exception: Unable to cast object of type 'System.Linq.Enumerable+WhereListIterator`1[Security.SecurityToken]' to type 'Security.SecurityToken'.

public class SecurityToken {

    public string body = "example";    
}    
public class Tokenizer {

        private static List<SecurityToken> allTokens = new List<SecurityToken>();

        public static async Task<bool> isTokenValid(string token)
        {
            SecurityToken foundToken = (SecurityToken)allTokens.Where(tk => tk.body == token);
            
            return foundToken.body.equals(token);                
        } 

}

Answer 1

As the error message read, you are casting System.Linq.Enumerable+WhereListIterator which is the result of your query allTokens.Where(tk => tk.body == token);to a SecurityToken which is wrong, a better approach is using FirstOrDefault ; but looking at your code, all you need is to check if any item meets a condition, so I suggest using Any .

return allTokens.Any(tk => tk.body == token);

Answer 2

Where returns a collection not a single object. You need to change code like below:

SecurityToken foundToken = allTokens
                            .Where(tk => tk.body == token)
                            .FirstOrDefault();

return (foundToken !=null);