创建可观察集合的通用列表派生

Question

I want to build an ObservableCollection that derrives from the basic ObservableCollection , in order to do certain things depending on the type of the children the Collection contains.

public class DbListBase : ObservableCollection<T>
{
    public DbListBase()
    {
        if (TypeOf(T) == Machine) {Do This}

        if (TypeOf(T) == Person) {Do That}
    }
}

However, the <T> is underlined with the errormessage Type or Namespace T not found.

I've tried to go around it, by using a base class, which all other classes inherit, like this.

public class DbListBase : ObservableCollection<ModelBase>
{
    public DbListBase()
    {
        // How would I check for the Type of child?
    }
}

But creating an instance of DbListBase won't let me do this:

DbListBase MachineList = new DbListBase<Machine>();

How can I make the first approach DbListBase : ObservableCollection<T> work?

Answer 1

The immediate reason for your error is: your class must be generic, too:

public class DbListBase<T> : ObservableCollection<T>
               // here ^^^^

But I don't like the idea of a generic type that does different things depending on the generic argument. Generic should be type- independent .

So I'd suggest to make different derivates for each type you need it for:

public class DbListBaseForType1 : ObservableCollection<Type1> // Type1 as generic argument for the base class
{
    // special behaviour for Type1
}

public class DbListBaseForType2 : ObservableCollection<Type2> // Type2 as generic argument for the base class
{
    // special behaviour for Type1
}