C# 多态性和模板

Question

This question may have been asked already, but I don't know the correct question to ask in order to find the answer.

I am attempting to make a set of classes (tags) that hold a value and allow other components to access the value.

The value is generic, which will allow you to create a Tag of any type. However I need to be able to hold the tags within a list or other data structure to allow the component to have multiple tags of multiple types.

  public abstract class BaseTag
  {
    protected object _value;
    public ushort DataQuality { get; protected set; }
    public virtual object Value => _value;
    public abstract void SetValue(object value, ushort dataQuality = 0);
  }

  public class Tag<T> : BaseTag
  {
    public new T Value
    {
      get => (T)_value;
      private set
      {
        _value = value;
      }
    }
    public override void SetValue(object value, ushort dataQuality = 0)
    {
      Monitor.Enter(_tagSync);

      try
      {
        //If value or quality haven't changed, then do nothing
        if (EqualityComparer<T>.Default.Equals((T)_value, (T)value) && dataQuality == DataQuality)
          return;

        DataQuality = dataQuality;
        Value = (T)value;
      }
      finally
      {
        Monitor.Exit(_tagSync);
      }
    }
  }

I don't even really know if I am asking the correct question still.

Can anyone help

How do I get the ability to have a List tags; tags[0].Value <- would like this to call the child value, but it doesn't, it returns the basetag._value, but of type object, not type

Is there an easier better way to make this happen?

Answer 1

do you really need the BaseTag class?

You can convert it to the interface and do with explicit interface declaration like below:

public interface IBaseTag
{
    object Value { get; }
    ushort DataQuality { get; }
}

public class Tag<T> : IBaseTag
{
    public T Value { get; set; }

    object IBaseTag.Value => Value; // explicit interface implementation

    public ushort DataQuality { get; protected set; }

    public virtual void SetValue(T value, ushort dataQuality = 0)
    {
        //If value or quality haven't changed, then do nothing
        if (EqualityComparer<T>.Default.Equals(Value, value) && dataQuality == DataQuality)
            return;

        DataQuality = dataQuality;
        Value = (T)value;
    }
}

I've skipped the _tagSync functional.

Then you can get the

var b = new Tag<int>(); //child
IBaseTag a = b; //parent

//a.Value and b.Value are both accessible and can be used
if (b.Value.Equals(a.Value) && a.DataQuality == b.DataQuality)
    return;

You can use the IBaseTag.Value or Tag<>.Value in the same time according to the dependency isolation.