使用反射将项添加到通用列表/集合

Question

I want to add an item to a Generic list using reflection. In the method "DoSomething", I am trying to finish the following line,

pi.PropertyType.GetMethod("Add").Invoke(??????)

but I am getting different kinds of error.

Below is my complete code

public class MyBaseClass
{        
    public int VechicleId { get; set; }        
}    
public class Car:MyBaseClass
{
    public string Make { get; set; }
}    
public class Bike : MyBaseClass
{
    public int CC { get; set; }
}        
public class Main 
{
    public string AgencyName { get; set; }
    public MyBaseCollection<Car> lstCar {get;set;}

    public void DoSomething()
    {
        PropertyInfo[] p =this.GetType().GetProperties();
        foreach (PropertyInfo pi in p)
        {
            if (pi.PropertyType.Name.Contains("MyBaseCollection"))
            {
                //Cln contains List<Car>
                IEnumerable<MyBaseClass> cln = pi.GetValue(this, null) as IEnumerable<MyBaseClass>;

                **//Now using reflection i want to add  a new car to my object this.MyBaseCollection**
                pi.PropertyType.GetMethod("Add").Invoke(??????)
            }
        }    
    }
}

Any ideas / suggestion ?

Answer 1

I think you want:

// Cast to IEnumerable<MyBaseClass> isn't helping you, so why bother?
object cln = pi.GetValue(this, null);

// Create myBaseClassInstance. 
// (How will you do this though, if you don't know the element-type?)
MyBaseClass myBaseClassInstance = ...

// Invoke Add method on 'cln', passing 'myBaseClassInstance' as the only argument.
pi.PropertyType.GetMethod("Add").Invoke(cln, new[] { myBaseClassInstance } );

Since you don't know what the element-type of the collection is going to be (could be Car, Bike, Cycle etc.) you're going to find it hard to find a useful cast. For example, although you say the collection will definitely implement IList<SomeMyBaseClassSubType> , that isn't all that helpful since IList<T> isn't covariant. Of course, casting to IEnumerable<MyBaseClass> should succeed, but that won't help you since it doesn't support mutations. On the other hand, if your collection-type implemented the non-generic IList or ICollection types, casting to those might come in handy.

But if you're sure that the collection will implement IList<Car> (ie you know the element-type of the collection beforehand), things are easier:

// A much more useful cast.
IList<Car> cln = (IList<Car>)pi.GetValue(this, null);

// Create car.
Car car = ...

// The cast helped!
cln.Add(car);

Answer 2

As an alternative... Just don't; consider the non-generic IList interface:

IList list = (IList) {... get value ...}
list.Add(newItem);

While it isn't obligatory for all generic collections to implement IList, they pretty much all do, since it underpins such a lot of core framework code.

Answer 3

以typeof<List<>>.GetMethods开头，你不要调用属性的方法，而是调用属性类型的方法

Answer 4

Could you just avoid reflection all together and use:

List<MyBaseClass> lstCar { get; set; }

lstCar.Add((MyBaseClass)new Car());

You could also consider using an interface or abstract methods...