How could I create an object collection with members from generic class?

Question

2.67/5 (3 votes)

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I want to add a member to a collection of a generic class, but it generates two errors as below:

Error   1   The best overloaded method match for 'Test.TransitionToolManager.Add(Test.StyleHandleCollection<object>)' has some invalid arguments

Error   2   Argument 1: cannot convert from 'Test.StyleHandleCollection<Test.Plane>' to 'Test.StyleHandleCollection<object>'

What am I doing wrong?
Here is the code:

namespace Test
{
    public interface ITransitionTool
    {
    }

    public class Plane : ITransitionTool
    {
    }

    public class Car : ITransitionTool
    {
    }

    public class Style
    {
        private Color mColor = new Color();
    }

    public class StyleHandle<T>
    {
        private List<T> mUserObjects = new List<T>();

        public void Adduser(T obj)
        {
            mUserObjects.Add(obj);
        }

        public void RemoveUser(T obj)
        {
            mUserObjects.Remove(obj);
        }
    }

    public class StyleHandleCollection<T>
    {
        public Dictionary<string, StyleHandle<T>> mDict = null;

        public StyleHandleCollection()
        {
            mDict = new Dictionary<string, StyleHandle<T>>();
        }
    }

    public class TransitionToolManager
    {
        private Dictionary<Type, StyleHandleCollection<object>> mCollection = null;

        public TransitionToolManager()
        {
            mCollection = new Dictionary<Type, StyleHandleCollection<object>>();
        }

        public void Add(StyleHandleCollection<object> collection)
        {
            mCollection.Add(typeof(object), collection);
        }
    }

    public class Document
    {
        private TransitionToolManager mMgr = null;

        public Document()
        {
            mMgr = new TransitionToolManager();
            StyleHandleCollection<Plane> planeStyles = new StyleHandleCollection<Plane>(); // error happens in this line...
            mMgr.Add(planeStyles);
        }
    }
}

Posted 23-Apr-11 22:39pm

DaveLand

Updated 24-Apr-11 15:18pm

v12

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Comments

R. Giskard Reventlov 24-Apr-11 4:47am

Well, sorry about that: can't seem to get it to format correctly. I'll remove the tags: perhaps someone else could try?

Ed Nutting 24-Apr-11 5:50am

Done. You needed top replace all the '<' and '>' signs with '<' and '>' then put <pre> blocks round the code and uncheck the 'Ignore HTML in this post' option.

R. Giskard Reventlov 24-Apr-11 11:36am

Thanks: not sure what came over me! :-)

DaveLand 24-Apr-11 21:12pm

Thanks for your correction.

2 solutions

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Ed Nutting · Answer 1 · 2011-04-23T23:47:00

Solution 1

Your issue seems to be that you pass Test.TransitionToolManager.Add a StyleHandleCollection of type Test.Plane when the method requires it to be of type object. You are trying to pass in the wrong collection type. Make your planeStyles of type StyleHandleCollection<object> and see if you still get the error.

Hope this helps,

Ed :)

Posted 23-Apr-11 23:47pm

Ed Nutting

Updated 23-Apr-11 23:51pm

v2

Comments

DaveLand 24-Apr-11 20:54pm

Thanks for your inputs, however, here I want to get a collection with different types.

Such as "mMgr = new TransitionToolManager();

StyleHandleCollection<plane> planeStyles = new StyleHandleCollection<plane>();

mMgr.Add(planeStyles); // Compile error happens in this line...

StyleHandleCollection<car> carStyles = new StyleHandleCollection<car>();

mMgr.Add(carStyles); ..."

And I don't want TransitionToolManager is a generic class too.

Ed Nutting 25-Apr-11 6:15am

Sorry I should have realised sooner, all you should have to do is cast the planeStyles to the correct type like so:

mMgr.Add((StyleHandleCollection<object>)planeStyles);

That should solve your problem. Ed :)

DaveLand 26-Apr-11 4:24am

Hi Ed,

Thanks for your response. I tested it, however it doesn't work well. The error changes as,
Error 1 Cannot convert type 'Test.StyleHandleCollection<test.plane>' to 'Test.StyleHandleCollection<object>'.

So it seems that it needs a basic class or interface for StyleHandleCollection<t> that can be used as a general value in the dictionary.
After I change StyleHandleCollection<t> derived from IStyleCollection and use it in the dictionary, it works.

DaveLand · Answer 2 · 2011-04-25T22:26:00

Here is my solution, though it is not perfect, it works. :)

namespace Test
{
    public interface ITransitionTool
    {
    }

    public class Plane : ITransitionTool
    {
    }

    public class Car : ITransitionTool
    {
    }

    public interface IStyleCollection
    {
    }

    public class Style
    {
        private Color mColor = new Color();
    }

    public class StyleHandle<T>
    {
        private List<T> mUserObjects = new List<T>();

        public void Adduser(T obj)
        {
            mUserObjects.Add(obj);
        }

        public void RemoveUser(T obj)
        {
            mUserObjects.Remove(obj);
        }
    }

    public class StyleHandleCollection<T> : IStyleCollection
    {
        public Dictionary<string, StyleHandle<T>> mDict = null;

        public StyleHandleCollection()
        {
            mDict = new Dictionary<string, StyleHandle<T>>();
        }
    }

    public class TransitionToolManager
    {
        private Dictionary<Type, IStyleCollection> mCollection = null;

        public TransitionToolManager()
        {
            mCollection = new Dictionary<Type, IStyleCollection>();
        }

        public void Add<T>(StyleHandleCollection<T> collection)
        {
            mCollection.Add(typeof(object), collection);
        }
    }

    public class Document
    {
        private TransitionToolManager mMgr = null;

        public Document()
        {
            mMgr = new TransitionToolManager();
            StyleHandleCollection<Plane> planeStyles = new StyleHandleCollection<Plane>();
            mMgr.Add(planeStyles);
        }
    }
}