Question

我有两个数据类： BaseDataClass 和 DerivedDataClass ，它们派生自第一个。我还有两个消费类： ConsumingBaseClass 和 ConsumingDerivedClass ，它们派生自第一个。在 ConsumingBaseClass 中，我有虚拟方法 DoWork ，它接受 DerivedDataClass < / strong>并做一些工作。

在 ConsumingDerivedClass 中，我对方法 DoWork 进行了覆盖，并且我还有 DoWork ，接受 BaseDataClass 。当我尝试调用 DoWork 时，传递 DerivedDataClass 的实例， DoWork（BaseDataClass）调用 而不是 DoWork（DerivedDataClass） 。

有没有人知道，为什么要调用错误的方法？

以下代码阐述了问题：

class Program { private static void Main(string[] args) { ConsumingDerivedClass x = new ConsumingDerivedClass(); // Wrong DoWork is called - expected calling of DoWork(DerivedDataClass) but actually called DoWork(BaseDataClass) x.DoWork(new DerivedDataClass()); Console.ReadKey(); } } public class ConsumingBaseClass { public virtual void DoWork(DerivedDataClass instance) { Console.WriteLine("ConsumingBaseClass.DoWork(DerivedDataClass); Type of argument is '{0}'", instance.GetType()); } } public class ConsumingDerivedClass : ConsumingBaseClass { public override void DoWork(DerivedDataClass instance) { Console.WriteLine("ConsumingDerivedClass.DoWork(DerivedDataClass); Type of argument is '{0}'", instance.GetType()); base.DoWork(instance); // Some additional logic } public void DoWork(BaseDataClass instance) { Console.WriteLine("ConsumingDerivedClass.DoWork(BaseDataClass); Type of argument is '{0}'", instance.GetType()); DerivedDataClass derivedInstance = new DerivedDataClass(); // Some logic based on what is in baseInstacne derivedInstance.SomeProperty = "Value, got from some logic"; base.DoWork(derivedInstance); // Some additional logic } } public class BaseDataClass { } public class DerivedDataClass : BaseDataClass { public string SomeProperty { get; set; } }

Answer 1

有没有人知道，为什么要调用错误的方法？

根据语言规范调用正确的方法。这是你的期望，这是错误的。

在ConsumingDerivedClass中，我有方法DoWork的覆盖，并且我对DoWork也有重载，它接受BaseDataClass。

基本上这就是问题所在。重载分辨率不会像您认为的那样工作。编译器从调用目标的编译时类型开始工作，直到基类到object。只考虑新声明的方法（甚至不被覆盖）。

您可以通过编写来更改将使用的重载：

((ConsumingBaseClass) x).DoWork(new DerivedDataClass());

理想情况下，如果你有一些这么脆弱的东西，那么给这些方法赋予不同的名称是值得的。过载应该具有相同的效果，只是以不同的方式提供信息。

基本上，请查看我brainteasers page上的第一个问题，以及第一个答案的详细信息。我也有article on overload resolution您可能会觉得有用。

Answer 2

尝试更改基本方法以使用BaseDataClass并覆盖它。提供派生数据特定版本作为“新”方法（根据@Jon Skeet的回答）

class Program
    {
        private static void Main(string[] args)
        {
            ConsumingDerivedClass x = new ConsumingDerivedClass();
            // Wrong DoWork is called - expected calling of DoWork(DerivedDataClass) but actually called DoWork(BaseDataClass) 
            x.DoWork(new DerivedDataClass());
            x.DoWork(new BaseDataClass());
            Console.ReadKey();
        }
    }

    public class ConsumingBaseClass
    {
        public virtual void DoWork(BaseDataClass instance)
        {
            Console.WriteLine("ConsumingBaseClass.DoWork(DerivedDataClass); Type of argument is '{0}'", instance.GetType());
        }
    }

    public class ConsumingDerivedClass : ConsumingBaseClass
    {
        public override void DoWork(BaseDataClass instance)
        {
            Console.WriteLine("ConsumingDerivedClass.DoWork(DerivedDataClass); Type of argument is '{0}'", instance.GetType());
            base.DoWork(instance);
            // Some additional logic 
        }

        public void DoWork(DerivedDataClass instance)
        {
            Console.WriteLine("ConsumingDerivedClass.DoWork(BaseDataClass); Type of argument is '{0}'", instance.GetType());
            DerivedDataClass derivedInstance = new DerivedDataClass();
            // Some logic based on what is in baseInstacne 
            derivedInstance.SomeProperty = "Value, got from some logic";

            base.DoWork(derivedInstance);
            // Some additional logic 
        }
    }

    public class BaseDataClass
    { }

    public class DerivedDataClass : BaseDataClass
    {
        public string SomeProperty { get; set; }
    }

.net根据参数类型选择错误的方法来调用

2 个答案: