当它可以是多种类型时，如何在不将其转换为一种类型的情况下访问“对象”的特定字段？

Question

I have an object that can be assigned different classes, all of which have a Position field which I need to access regardless of the object's type. Visual Studio won't let me compile var pos = myObject.Position because object doesn't have a Position field. And I can't cast to MyClass , because there can be several other classes assigned to that variable.

How do I access the Position field without casting to one type?

Answer 1

The best option would be to make all of your classes implement a common interface, and then use that interface to access the properties.

However, if these are classes outside of your control, there are other options. You could use Reflection to access the field/property (via Type.GetField and FieldInfo.GetValue , etc), though this is slow at runtime.

If you're using C# 4 or later, you can use dynamic :

dynamic theObject = yourObject;
Point position = theObject.Position;

This will use dynamic (runtime) binding to find the Position property or field on your type.

Answer 2

All of those different classes which have a Position field should either inherit that field from a common base class, or get it (it would have to be a property then) from a common interface.

The interface solution might look like this:

interface IHasPosition
{
  int Position { get; }
}

then all of the classes shall say : IHasPosition , and your myObject variable should be declared of type IHasPosition in the code.

Answer 3

Once option is to make all of the different classes inherit from a class which defines Position then when you get the object refer to it by the parent classes type and you can access the properties that are defined there without knowing the specific type.

Keep in mind if they don't have much common functionality this may not be a very good approach.