C#中接口成员的访问修饰符
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Access modifiers on interface members in C#
提问by benPearce
I am getting a compile error from the following property.
The error is:
我从以下属性收到编译错误。
错误是：
"The modifier 'public' is not valid for this item"
“修饰符‘public’对此项无效”
public System.Collections.Specialized.StringDictionary IWorkItemControl.Properties
{
get { return properties; }
set { properties = value; }
}
but if I remove the IWorkItemControlit compiles fine.
但如果我删除IWorkItemControl它编译正常。
Why am I getting this error and what is the difference of having / not having the interface name in the signature?
为什么我会收到此错误，签名中有/没有接口名称有什么区别？
采纳答案by Mehrdad Afshari
Explicit interface implementationdoes not let you specify any access modifiers. When you implement an interface member explicitly (by specifying the interface name before the member name), you can access that member only using that interface. Basically, if you do:
显式接口实现不允许您指定任何访问修饰符。当您显式实现接口成员时（通过在成员名称之前指定接口名称），您只能使用该接口访问该成员。基本上，如果你这样做：
System.Collections.Specialized.StringDictionary IWorkItemControl.Properties
{
get { return properties; }
set { properties = value; }
}
You can't do:
你不能这样做：
MyClass x = new MyClass();
var test = x.Properties; // fails to compile
// You should do:
var test = ((IWorkItemControl)x).Properties; // accessible through the interface
There are several use cases for EII. For example, you want to provide a Closemethod for your class to free up acquired resources but you still want to implement IDisposable. You could do:
EII 有几个用例。例如，您想Close为您的类提供一个方法来释放获得的资源，但您仍然想实现IDisposable. 你可以这样做：
class Test : IDisposable {
public void Close() {
// Frees up resources
}
void IDisposable.Dispose() {
Close();
}
}
This way, the consumers of class can only call Closedirectly (and they won't even see Disposein Intellisense list) but you can still use the Testclass wherever an IDisposableis expected (e.g. in a usingstatement).
这样，类的使用者只能Close直接调用（他们甚至不会Dispose在 Intellisense 列表中看到），但您仍然可以在预期的Test任何地方IDisposable（例如在using语句中）使用该类。
Another use case for EII is providing different implementations of an identically named interface member for two interfaces:
EII 的另一个用例是为两个接口提供同名接口成员的不同实现：
interface IOne {
bool Property { get; }
}
interface ITwo {
string Property { get; }
}
class Test : IOne, ITwo {
bool IOne.Property { ... }
string ITwo.Property { ... }
}
As you see, without EII it's not even possibleto implement both interfaces of this example in a single class (as the properties differ just in return type). In other cases, you might want to intentionally provide different behavior for individual views of a class through different interfaces.
如您所见，如果没有 EII，甚至不可能在单个类中实现此示例的两个接口（因为属性仅在返回类型上有所不同）。在其他情况下，您可能希望通过不同的接口为类的各个视图有意提供不同的行为。
回答by abelenky
All elements of an interface must be public. After all, an interface isthe public view of an object.
接口的所有元素都必须是公共的。毕竟，接口是对象的公共视图。
Since Propertiesis an element of an interface IWorkItemControl, it is already public, and you cannot specify its access level, even to redundantly specify that it is public.
由于Properties是接口IWorkItemControl 的一个元素，它已经是公共的，您不能指定它的访问级别，甚至多余地指定它是公共的。
