是否可以从 C# 中的通用对象集合中提取特定字段值的列表？

Question

I have the following method in a class I am using for pagination in my app:

public static PagedList<T> ToPagedList(IEnumerable<T> source, int pageNumber, int pageSize)
        {
            var count = source.Count();
            var items = source
              .Skip((pageNumber - 1) * pageSize)
              .Take(pageSize).ToList();

            return new PagedList<T>(items, count, pageNumber, pageSize);
        }

In this method I am passing in a collection of generic objects as IEnumerable<T> source which regardless of type will always have an Id field. What I'd like to do is pull out all of the Ids for these objects and store them in a list to be passed into my PagedList constructor. Is this possible?

Answer 1

Yes it is possible. You can use Reflection<\/a> to get the value of a property.

item.GetType().GetProperty("Id").GetValue(item, null);

Answer 2

the best way would be create an interface

public interface IBaseClass{
  public int Id {get; set;}
}

Answer 3

An interface would be the best way, but you specifically said "field" and interfaces cannot contain fields.

You could get around this limitation with an abstract base class, but you cannot have multiple base classes on a single class (if applicable).

...All of this assumes that you have the ability to modify those classes.

Another way to do this would be:

public static PagedList<T> ToPagedList<T>(IEnumerable<T> source, int pageNumber, int pageSize)
{
    var count = source.Count();

    var items = source
        .Skip((pageNumber - 1) * pageSize)
        .Take(pageSize).ToList();

    var ids = items
        .Select(i => ((dynamic)i).Id)   // field is **always** named "Id"
        .Cast<int>()                    // its type is **always** int
        .ToList();
            
    return new PagedList<T>(items, count, pageNumber, pageSize/*, ids*/); // pass ids
}

This assumes the field in question is named "Id", and it is an int .

Adjust accordingly and handle potential errors.

I think I originally misunderstood the question, the comment by @Dusan caused me to reevaluate and update the code.