实现泛型类的集合

Question

I am trying to create a custom class like this as follows.

public MyClass<T> 
{
    public string Value1 { get; set; }
    public T Value2 { get; set; }
    public string Value3 { get; set; }
}

The value of T could be either string or int or datetime .I assume i can create new instance of this class like

MyClass<int> intclass = new MyClass<int>();
MyClass<String> stringclass=new MyClass<String>();

and so forth.

Is it possible to create a collection of the above classes where i can put intclass and stringclass into a custom collection.

Answer 1

If you want to mix different generic types (so have a collection containing both MyClass<int> and MyClass<string> ) you need to define some common base type or use a collection that is not strongly typed:

public class MyClass<T> : MyClass
{
    public T Value2 { get; set; }
}

public class MyClass
{
    public string Value1 { get; set; }
    public string Value3 { get; set; }
}

Then you can define a collection like:

List<MyClass> list = new List<MyClass>();
list.Add(new MyClass<int>());
list.Add(new MyClass<string>());

You will have to cast results when retrieving entries in order to access their Value2 property though.

Another option to avoid the base-class is simply to use a List<object> :

List<object> list = new List<object>();
list.Add(new MyClass<int>());
list.Add(new MyClass<string>());

But it's the same problem as above, but plausibly worse (because then you can store anything in there)

EDIT: There are various ways of how to allow untyped access to Value2 in the base non-generic MyClass . One way is to define an "untyped" version of it on the base class and override it on the subclass which would perform type-checking:

public abstract class MyClass
{
    public string Value1 { get; set; }
    public abstract object Value2Untyped { get; set; }
    public string Value3 { get; set; }
}

public class MyClass<T> : MyClass
{
    public T Value2 { get; set; }

    public override object Value2Untyped
    {
        get
        {
            return Value2;
        }
        set
        {
            Value2 = (T)value;
        }
    }
}

Then for all your objects or collections that are typed against the base non-generic MyClass , you can still access values, and even set values at runtime. (the set of course is optional)

Answer 2

you mean something like this?

List<MyClass<int>> intClassList = new List<MyClass<int>>();
intClassList.Add(new MyClass<int>());