编译错误: 在显式实现接口时“修饰符‘ public’对此项无效”

我在一个类上创建一个用于显式实现 interface的 public方法时遇到了这个错误。我有一个变通方法: 通过删除 PrintName方法的显式实现。但是我很惊讶为什么我会得到这个错误。

有人能解释一下这个错误吗？

图书馆代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


namespace Test.Lib1
{


public class Customer : i1
{
public string i1.PrintName() //Error Here...
{
return this.GetType().Name + " called from interface i1";
}
}


public interface i1
{
string PrintName();
}


interface i2
{
string PrintName();
}
}

控制台测试代码应用程序:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Test.Lib1;


namespace ca1.Test
{
class Program
{
static void Main(string[] args)
{
Customer customer = new Customer();
Console.WriteLine(customer.PrintName());


//i1 i1o = new Customer();
//Console.WriteLine(i1o.printname());


//i2 i2o = new Customer();
//Console.WriteLine(i2o.printname());


}
}
}
102024 次浏览
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You cannot use access modifiers when implementing interface explicitly. Member will be binded to the interface anyway, so it is no need to specify access modifier, because all interface members are always public, also all explicitly implemented members can be accessed only through member of interface type (see statichippo's answer for example).

小开

http://msdn.microsoft.com/en-us/library/aa288461(VS.71).aspx : When a member is explicitly implemented, it cannot be accessed through a class instance, but only through an instance of the interface.

Customer customer = new Customer();

Console.WriteLine(customer.PrintName());

Violates this

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最佳答案

When using explicit implementation of an interface, the members are forced to something more restricted than private in the class itself. And when the access modifier is forced, you may not add one.

Likewise, in the interface itself, all members are public. If you try to add a modifier inside an interface you will get a similar error.

为什么显式成员（非常）隐私？考虑:

interface I1 { void M(); }
interface I2 { void M(); }


class C : I1, I2
{
void I1.M() { ... }
void I2.M() { ... }
}


C c = new C();
c.M();         // Error, otherwise: which one?
(c as I1).M(); // Ok, no ambiguity.

If those methods were public, you would have a name-clash that cannot be resolved by the normal overload rules.

For the same reason you cannot even call M() from inside a class C member. You will have to cast this to a specific interface first to avoid the same ambiguity. 

class C : I1, I2
{
...
void X()
{
M();             // error, which one?
((I1)this).M();  // OK
}
}
小开

When we want to go with implicit implementation for the above example, following would be the code.

    interface I1 { void M(); }
interface I2 { void M(); }


class C : I1, I2
{
public void M() { ... }
}


C c = new C();
c.M();  // Ok, no ambiguity. Because both Interfaces gets implemented with one    method definition.
小开

This is an Explicit implementation, the default scope for the members of the interface is public, whereas it is private in case of a class, ergo, there is no need to use the Public modifier because when we call that method it would be called with the reference of the interface only.

According to "MSDN Explicit Interface Implementation" the functions that implement explicit interfaces are never explicitly defined public. They are public by default. It would be meaningless to define them otherwise.


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