使用反射调用静态类中静态属性的非静态成员

Question

I have a static class which looks for an implementation of an abstract type and stores it as a static property similar to the below:

public static class MyStaticClass
{
    private static MyAbstractType _MyAbstractImplementation;

    public static MyAbstractType MyAbstractImplementation
    {
        get => _MyAbstractImplementation ?? ( _MyAbstractImplementation = FindImplementation());
        private set => _MyAbstractImplementation = value;
    }
}

And I am trying to call a method of MyAbstractImplementation (which contains no static properties or methods) via reflection:

var myAssembly = Assembly.Load("MyStaticClassAssembly")

var myType = myAssembly.GetTypes().First(t => t.Name == "MyAbstractType");

var myImplementation = myType.GetProperties()
    .First(p=>p.ReflectedType?.Name == "MyAbstractImplementation")
    .GetValue(null);

var obj = myType.GetMethod("SomeMethod")?.Invoke(
                null,
                new object[] 
                {
                    // Some args
                });

The above code causes the following exception on getting the value of MyAbstractImplementation :

System.Reflection.TargetException: Non-static method requires a target.

Evidently, this is because I am passing null to GetValue() , so I try passing myAssembly rather than null and I get the following exception:

System.Reflection.TargetException: Object does not match target type.

Out of desperation, I try passing myType and myImplementation but I still get the same exception.

What am I meant to be passing to GetValue() ?

Answer 1

From the error you are getting MyAbstractImplementation is not a static property, so it needs an instance to be run on. You are basically trying to write the following code:

new MyAbstractType().MyAbstractImplementation.SomeMethod();

Both the property and method access need the target to run against (the left side of '.'). So you need an instance of myType . Also the method will need the instance, which is the result of getting the property ( myImplementation ).

var myAssembly = Assembly.Load("MyStaticClassAssembly");

var myType = myAssembly.GetTypes().First(t => t.Name == "MyAbstractType");
var myTypeInstance = Activator.CreateInstance(myType);  // Asuming has a default constructor 

var myImplementation = myType.GetProperties()
    .First(p => p.ReflectedType?.Name == "MyAbstractImplementation")
    .GetValue(myTypeInstance);

var obj = myType.GetMethod("SomeMethod")?.Invoke(
                myImplementation,
                new object[]
                {
                    // Some args
                });

From how you write the code myImplementation should also be of type myType ( myType.GetMethod("SomeMethod") ) if it isn't replace it with: myImplementation.GetType().GetMethod("SomeMethod") .