如何对具有相同成员的不同类型参数使用相同的函数？

Question

BHere is the sample code, I've defined two classes. How can I use the Output function to output the member which has the same name in two different classes?

class A
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Email { get; set; }

    public A(string name, int age, string email)
    {
        Name = name;
        Age = age;
        Email = email;
    }
}

class B
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Location { get; set; }

    public B(string name, int age, string location)
    {
        Name = name;
        Age = age;
        Location = location;
    }
}

void Output(object obj)
{
    // How can I convert the object 'obj' to class A or class B
    // in order to output its 'Name' and 'Age'
    Console.WriteLine((A)obj.Name); // If I pass a class B in pararmeter, output error.
}

Answer 1

You'd have to either:

1. Use Reflection to get the property (and throw if it isn't there)
2. Have a common interface, such as INamed that has a string Name property, that each of the two classes implement
3. Declare a local variable as dynamic and use it to access the Name property (but in effect this is the same as #1, because the dynamic dispatch will merely use Reflection to get the Name property).

Answer 2

You can take advantage of dynamic to bypass the compiler, it checks the type at runtime so you don't need to cast:

void Output(dynamic obj)
{
    Console.WriteLine(obj.Name); 
}

Answer 3

You should declare an interface which will describe the common part of both classes:

interface I
{
    string Name { get; set; }
    int Age { get; set; }
}

Then implement it in both A and B :

class A : I
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Email { get; set; }

    public A(string name, int age, string email)
    {
        Name = name;
        Age = age;
        Email = email;
    }
}

class B : I
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Location { get; set; }

    public B(string name, int age, string location)
    {
        Name = name;
        Age = age;
        Location = location;
    }
}

And change your method to get I as parameter:

void Output(I obj)
{
    Console.WriteLine(obj.Name); 
}

Answer 4

You could use dynamic , reflection, or inheritance. Or you could just duplicate the method and take advantage of method overloading

void Output(A obj)
{
 // in order to output its 'Name' and 'Age'
 Console.WriteLine(obj.Age);
 Console.WriteLine(obj.Name);
}

void Output(B obj)
{
 // in order to output its 'Name' and 'Age'
 Console.WriteLine(obj.Age);
 Console.WriteLine(obj.Name);
}

Answer 5

You need to create a common interface for both classes, so the compiler knows that both classes can dliver certain features (Name and age in your case):

    interface IHasNameAndAge
    {
        string Name { get; }
        int Age { get; }
    }

    class A : IHasNameAndAge
    {
        public string Name { get; set; }
        public int Age { get; set; }
        string Email { get; set; }

        public A(string name, int age, string email)
        {
            Name = name;
            Age = age;
            Email = email;
        }
    }

    class B : IHasNameAndAge
    {
        public string Name { get; set; }
        public int Age { get; set; }
        string Location { get; set; }

        public A(string name, int age, string location)
        {
            Name = name;
            Age = age;
            Location = location;
        }
    }

    void Output(IHasNameAndAge obj)
    {
        Console.WriteLine(obj.Name + " is " + obj.Age);
    }

Answer 6

In your case - B does not inheret from A, so you cannot cast B to A.

Change B to inherit from A, like

class B : A
{
...
}

Also - consider what are you trying to accomplish in your A() method of B class. And - if you inherited, you probably need not same members to be declared twice.

Answer 7

You could do:

if ( obj.GetType() == typeof( A ) )
{
    Console.WriteLine(((A)obj).Name);
}
else if ( obj.GetType() == typeof( B ) )
{
    Console.WriteLine(((B)obj).Name);
}