CODEWITHSUNDEEP
c#
mrblah
mrblah

Reputation: 103627

set operation on a property return IList is not working

I have an interface with:

IList<int> CategoryIDs {get;set;}

Then a class that inherits this interface:

public IList<int> CategoryIDs
{

     get {}  // this part works
     set { _categoryIDs = value;   // error!

}

The set part of the accessor reports an error:

cannot implicity convert type IList<int> to List<int>.

What should I do? confused.

Upvotes: 0

Views: 3393

Answers (5)

Aleana Keiko Perry
Aleana Keiko Perry

Reputation: 1

Your set function is missing the second bracket.

Upvotes: -1

Reed Copsey
Reed Copsey

Reputation: 564691

Two things:

1) It's usually a bad idea to put a setter on an IList<T> member. You typically want people to work on your existing list, but not replace it completely. This would look like:

public interface IMyInterface {
    IList<int> CategoryIDs {get;} // Only put get
}

public class MyClass : IMyInterface
{
     List<int> categoryIDs;

     public IList<int> CategoryIDs
     {
          get { return this.categoryIDs; }
     }
}

2) If you do need to do that, you'll have to either cast the IList<T> to a List<T> in order to set it, or make a copy. 

public interface IMyInterface {
    IList<int> CategoryIDs {get;set;} 
}

public class MyClass : IMyInterface
{
     List<int> categoryIDs;

     public IList<int> CategoryIDs
     {
          get { return this.categoryIDs; }
          set
          {
                List<int> asList = value as List<int>;
                if (asList != null)
                    this.categoryIDs = asList;
                else
                    this.categoryIDs = new List<int>(value); // Copy values across into new list!
          }
     }
}

Either way, this approach is a bit "clunky" feeling.

Upvotes: 2

Larsenal
Larsenal

Reputation: 51186

You can instantiate and assign a List just fine with a minor tweak:

private IList<int> _categoryIDs; // use IList instead of List
public IList<int> CategoryIDs
{

     get { return _categoryIDs; }
     set { _categoryIDs = value; }

}

Upvotes: 1

Pavel Minaev
Pavel Minaev

Reputation: 101605

Apparently, your field _categoryIDs is declared as List<T>, while your property is IList<T> (or even IList, it's hard to say with broken source code formatting in the question). IList<T> (and IList) is an interface; List<T> is a class implementing that interface. Because of that, you can assign List reference to variable of type IList, but not vice versa.

Upvotes: 0

Ed Swangren
Ed Swangren

Reputation: 124732

IList is an interface, List is a concrete class. List may implement IList, but other classes may as well, so you cannot assign an IList to a List without a cast. Try something like this instead:

private IList<int> _list = new List();
public IList<int> List
{
    get { return _list; }
    set { _list = value; }
}

Of course, you should not be writing code in your class that assumes that List or _list is actually a list, you should be treating it generically as an IList.

Upvotes: 2

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