我在VS2010中有两个选项来实现接口。
当我有如下的 IHelper.cs 接口：
public interface IHelper
....
IEnumerable<IPort> Ports { get; }
“显式实现接口”会给出以下代码：
IEnumerable<IPort> IHelper.Ports
{
get
{
...
}
}
而且，“实现接口”给了我这段代码：
public IEnumerable<IPort> Ports
{
get
{
...
}
}
它们是相同的还是不同的？为什么在C#中实现接口有两种选项？
显式接口声明意味着接口成员只能在该接口本身上使用，因此实现类型在公开访问它们之前需要将其强制转换为该接口。
隐式声明是实现大多数接口的标准方式，将接口项暴露在实现者类型的公共API上。
显式接口定义的主要原因是避免命名冲突，如果您碰巧实现了包含具有相同签名的方法的两个接口...显式定义允许编译器保持足够不同的签名以便解决问题。
支持代码维护的次要原因，如XenoPuTtSs在评论中建议的那样，是显式定义将在实现类型上触发编译器错误，如果删除了方法签名。对于隐式实现，从接口中删除方法会使该方法成为任何类型的常规成员 - 这意味着您现在需要手动搜索已失效的方法实现。
public interface IFoo {
String Bar { get; set; }
}
public class ImplicitFoo : IFoo {
public string Bar {get;set;}
}
public class ExplicitFoo : IFoo {
private String _Bar;
string IFoo.Bar {
get {
return _Bar;
}
set {
_Bar = value;
}
}
}
public class Test {
public void Test() {
var iml = new ImplicitFoo();
// Works fine
Console.WriteLine(iml.Bar);
var expl = new ExplicitFoo();
var fooInterface = (IFoo)expl;
// Works fine
Console.WriteLine(fooInterface.Bar);
// Throws compile time exception
Console.WriteLine(expl.Bar);
}
}
实现接口的类可以显式实现该接口的成员。当成员被显式实现时，它不能通过类实例访问，只能通过接口实例访问。
// explicit1.cs
interface IDimensions
{
float Length();
float Width();
}
class Box : IDimensions
{
float lengthInches;
float widthInches;
public Box(float length, float width)
{
lengthInches = length;
widthInches = width;
}
// Explicit interface member implementation:
float IDimensions.Length()
{
return lengthInches;
}
// Explicit interface member implementation:
float IDimensions.Width()
{
return widthInches;
}
public static void Main()
{
// Declare a class instance "myBox":
Box myBox = new Box(30.0f, 20.0f);
// Declare an interface instance "myDimensions":
IDimensions myDimensions = (IDimensions) myBox;
// Print out the dimensions of the box:
/* The following commented lines would produce compilation
errors because they try to access an explicitly implemented
interface member from a class instance: */
//System.Console.WriteLine("Length: {0}", myBox.Length());
//System.Console.WriteLine("Width: {0}", myBox.Width());
/* Print out the dimensions of the box by calling the methods
from an instance of the interface: */
System.Console.WriteLine("Length: {0}", myDimensions.Length());
System.Console.WriteLine("Width: {0}", myDimensions.Width());
}
}
显式接口实现还允许程序员继承共享相同成员名称的两个接口，并为每个接口成员提供单独的实现。本示例显示了一个盒子的尺寸，包括公制和英制单位。Box类继承了两个接口IEnglishDimensions和IMetricDimensions，它们代表不同的测量系统。两个接口都具有相同的成员名称Length和Width。
请看示例：
// explicit2.cs
// Declare the English units interface:
interface IEnglishDimensions
{
float Length();
float Width();
}
// Declare the metric units interface:
interface IMetricDimensions
{
float Length();
float Width();
}
// Declare the "Box" class that implements the two interfaces:
// IEnglishDimensions and IMetricDimensions:
class Box : IEnglishDimensions, IMetricDimensions
{
float lengthInches;
float widthInches;
public Box(float length, float width)
{
lengthInches = length;
widthInches = width;
}
// Explicitly implement the members of IEnglishDimensions:
float IEnglishDimensions.Length()
{
return lengthInches;
}
float IEnglishDimensions.Width()
{
return widthInches;
}
// Explicitly implement the members of IMetricDimensions:
float IMetricDimensions.Length()
{
return lengthInches * 2.54f;
}
float IMetricDimensions.Width()
{
return widthInches * 2.54f;
}
public static void Main()
{
// Declare a class instance "myBox":
Box myBox = new Box(30.0f, 20.0f);
// Declare an instance of the English units interface:
IEnglishDimensions eDimensions = (IEnglishDimensions) myBox;
// Declare an instance of the metric units interface:
IMetricDimensions mDimensions = (IMetricDimensions) myBox;
// Print dimensions in English units:
System.Console.WriteLine("Length(in): {0}", eDimensions.Length());
System.Console.WriteLine("Width (in): {0}", eDimensions.Width());
// Print dimensions in metric units:
System.Console.WriteLine("Length(cm): {0}", mDimensions.Length());
System.Console.WriteLine("Width (cm): {0}", mDimensions.Width());
}
}
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