1.  IsAssignableFrom实例方法 判断一个类或者接口是否继承自另一个指定的类或者接口。

public interface IAnimal { }
public interface IDog : IAnimal { }
public class Dog : IDog { }
public class Cate : IAnimal { }
public class Parrot { }
    	

var iAnimalType = typeof(IAnimal);
var iDogType = typeof(IDog);
var dogType = typeof(Dog);
var cateType = typeof(Cate);
var parrotType = typeof(Parrot);

Console.WriteLine(iAnimalType.IsAssignableFrom(iDogType)
    ? $"{iDogType.Name} was inherited from {iAnimalType.Name}"
    : $"{iDogType.Name} was not inherited from {iAnimalType.Name}");

Console.WriteLine(iAnimalType.IsAssignableFrom(dogType)
    ? $"{dogType.Name} was inherited from {iAnimalType.Name}"
    : $"{dogType.Name} was not inherited from {iAnimalType.Name}");

Console.WriteLine(iDogType.IsAssignableFrom(dogType)
    ? $"{dogType.Name} was inherited from {iDogType.Name}"
    : $"{dogType.Name} was not inherited from {iDogType.Name}");

Console.WriteLine(iAnimalType.IsAssignableFrom(cateType)
    ? $"{cateType.Name} was inherited from {iAnimalType.Name}"
    : $"{cateType.Name} was not inherited from {iAnimalType.Name}");

Console.WriteLine(iAnimalType.IsAssignableFrom(parrotType)
    ? $"{parrotType.Name} inherited from {iAnimalType.Name}"
    : $"{parrotType.Name} not inherited from {iAnimalType.Name}");
Console.ReadKey();

输出结果：

IDog was inherited from IAnimal
Dog was inherited from IAnimal
Dog was inherited from IDog
Cate was inherited from IAnimal
Parrot not inherited from IAnimal

2.IsInstanceOfType 判断某个对象是否继承自指定的类或者接口

Dog d=new Dog();
var result=typeof(IDog).IsInstanceOfType(d);
Console.WriteLine(result? $"Dog was inherited from IDog": $"Dog was not inherited from IDog");
Console.ReadKey();

输出结果：

Dog was inherited from IDog

3.IsSubclassOf 判断一个对象的类型是否继承自指定的类，不能用于接口的判断，只能用于判定类的关系

public interface IAnimal { }
public interface IDog : IAnimal { }
public class Dog : IDog { }
public class Husky : Dog { }
public class Cate : IAnimal { }
public class Parrot { }

Husky husky = new Husky();
var result = husky.GetType().IsSubclassOf(typeof(Dog));
Console.WriteLine(result ? $"Husky was inherited from Dog" : $"Husky was not inherited from Dog");

输出结果：

Husky was inherited from Dog

这个方法不能用于接口，如果传接口进去永远返回的都是false

Dog dog = new Dog();
var dogResult = dog.GetType().IsSubclassOf(typeof(IDog));
Console.WriteLine(dogResult);

结果：

false