Initialize IList<T> C#

Question

Hi SO:

Is there a particular way to initialize an IList<T>? This does not seem to work:

IList<ListItem> allFaqs = new IList<ListItem>();
// Error I get here: Cannot create an instance of the interface 'IList<ListItem>'

ReSharper suggests to initialize it like so:

IList<ListItem> allFaqs = null;

But won't that cause a Null Reference Exception when I go to add items to this list?

Or should I just use List<ListItem>?

Thanks!

Answer 1

You need to do:

IList<ListItem> allFaqs = new List<ListItem>();

In your code you are trying to initialize an interface.

Answer 2

IList is an interface so you can't instantiate it. All sorts of classes implement IList. One such class that implements IList is List. You can instantiate it like so:

List<ListItem> allFaqs = new List<ListItem>();

Answer 3

Your problem is that IList is an interface, not a class. You can't initialize an interface.

You can have an instance of an interface, but you need to initialize it with a class that implements that interface such as:

IList<string> strings = new List<string>();

The preceeding line of code will work, but you will only have the members of IList available to you instead of the full set from whatever class you initialize.

Answer 4

The error is because you're trying to create an instance of the interface.

Change your code to:

List<ListItem> allFaqs = new List<ListItem>();

and it should compile.

You'll obviously have to change the rest of your code to suit too.

Answer 5

You can't instantiate an interface (IList is an interface).

You would need to instantiate something that implements an IList,

like so:

IList<ListItem> allFaqs = new List<ListItem>();

There are other kinds of ILists, but List is a good one to start with.

Answer 6

IList<T> is an interface. You need to instantiate a class that implements the interface:

IList<ListItem> allFaqs = new List<ListItem>();

List<T> implements IList<T>, and so can be assigned to the variable. There are also other types that also implement IList<T>.

Answer 7

IList is an Interface, not a class. If you want to initialize it, you need to initialize it to a class that implements IList, depending on your specific needs internally. Usually, IList is initialized with a List.

IList<ListItem> items = new List<ListItem>();

Answer 8

IList is not a class; it's an interface that classes can implement. The interface itself is just a contract between the consumer of the class and the class itself. This line of code will work:

IList<ListItem> allFaqs = new List<ListItem>();

Does this help?