Type T, object, & List

Question

I have a method that receives an object parameter. In some instances, the actual type is a List of unknown type. I need to cast the parameter to a List and process the list items. I got close using Type.IsGenericType and GetGenericArguments(). Does anyone know how to do this?

Sam Hobbs · Answer

The answer might depend on what you need to do with the items. If you need to serialize them, then there might be easier solutions. What I would do is to put a line such as: Type t = p.GetType(); in my program then set a breakpoint on that line or the line after it. Then I would look at the Type. I think you will see that the type name is something such as List`1 but I am notsure what the `1 is. There is other data, such as the namespace name, that might help. As I say, I am not sure what you need to do. Something else that migh help is (assuming that o is the object that might be a List): List l = o as List ; if (l != null) foreach (object io in l) { t = io.GetType(); Console.WriteLine(t); }

Cody Skidmore · Answer

>my friend, you are doing it all wrong, Well, yeah. I know I've got it all wrong. :-) But that one line of code doesn't explain how to get the items out of the list and into a List right? That is the problem I'm solving. There must be a way to getting items out of the parameter or a cast I don't know about. I actually tried casting/creating a List in one variation, but it throws an exception saying the LINQ entity isn't an object.

Roei Bar · Answer

my friend, you are doing it all wrong, create a list ; and then run the foreach loop on this Objects List.

Cody Skidmore · Answer

This should illustrate the problem: protected string GetParameterValue(object value) { if (value.GetType().IsGenericType) { Type listItemType = value.GetType().GetGenericArguments()[0]; /// listItemType is a class (In this case, a LINQ entity) /// that doesn't extend object. Then the cast fails. } if (value.GetType().IsGenericType) { StringBuilder sb = new StringBuilder(); List values = (List )value; for(Int32 i = 0; i sb.Append(values[i].ToString()); return sb.ToString(); } else return value.ToString(); } I tried variations of the following sytax before starting this post but can't get it working: Type listItemType = value.GetType().GetGenericArguments()[0]; List list = (List )value; foreach(listItemType item in list) { /// process the item.. }

Roei Bar · Answer

if you are using List which means its any kind of type, in order to cast the object you will have to call the GetType() Method and cast based on the Response. if its a Base T List like this List , it means that T is of a list of Known Types meaning like this List : where T is Product and Product is all kind of objects that inherit from it. and then you can know exactly what T is

Type T, object, & List

Answers (5)