使用反射获取类中列表属性的计数属性值

Question

I have the following classes:

class Topping
{
   public string Name {get; set;}
}

class Pizza
{
    public List<Topping> Toppings {get ; set;}

    public Pizza()
    {
       this.Toppings = new List<Topping>();
    }
}

Suppose i have a list of pizzas inside Main

Is there a way to get the value of the Count property of the Toppings list inside the Pizza class, using reflection ?

I tried something like this:

foreach(var pizza in Pizza)
{
   int countValue = pizza.GetType().GetProperty("Toppings").GetType().GetProperty("Count").GetValue(pizza);
}

Answer 1

When calling GetValue , you should provide instances of pizza and list , eg (if you insist on reflection):

foreach (var pizza in Pizza) {
  var list = pizza
    .GetType()
    .GetProperty("Toppings")
    .GetValue(pizza); // we want list of Toppings for the pizza instance
 
  int countValue = (int) (list 
    .GetType()
    .GetProperty("Count")
    .GetValue(list)); // we want Count for list (i.e. pizza.Toppings) instance    
}

Straightforward coding will be

foreach (var pizza in Pizza) {
  // If pizza or Toppings is null, let's have -1 for countValue
  int countValue = pizza
    ?.Toppings
    ?.Count ?? -1; 
}

Answer 2

I agree with Dmitry Bychenko, but I think in real case you don't need to use Reflection.

Event if you don't know the type of the list ( Topping in your case), you can always cast a list to ICollection.

The definition of list is this:

public class List<T> : ICollection<T>, IEnumerable<T>, IEnumerable, IList<T>, IReadOnlyCollection<T>, IReadOnlyList<T>, ICollection, IList

And ICollection has a Count property.

 /// <summary>Defines size, enumerators, and synchronization methods for all nongeneric collections.</summary>
  public interface ICollection : IEnumerable
  {
    /// <summary>Gets the number of elements contained in the <see cref="T:System.Collections.ICollection"></see>.</summary>
    /// <returns>The number of elements contained in the <see cref="T:System.Collections.ICollection"></see>.</returns>
    int Count { get; }

So this code should works:

var count = (pizza.Topping as ICollection).Count;