如何：显式实现两个接口的成员（C# 编程指南） · MSDN C# 编程指南 & 参考手册 2015

# 如何：显式实现两个接口的成员（C# 编程指南）显式[接口](https://msdn.microsoft.com/zh-CN/library/87d83y5b.aspx)实现还允许程序员实现具有相同成员名称的两个接口，并为每个接口成员各提供一个实现。本示例同时以公制单位和英制单位显示框的尺寸。Box [类](https://msdn.microsoft.com/zh-CN/library/0b0thckt.aspx)实现 IEnglishDimensions 和 IMetricDimensions 两个接口，它们表示不同的度量系统。两个接口有相同的成员名称 Length 和 Width。 ``` // 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; } static void Main() { // Declare a class instance box1: Box box1 = new Box(30.0f, 20.0f); // Declare an instance of the English units interface: IEnglishDimensions eDimensions = (IEnglishDimensions)box1; // Declare an instance of the metric units interface: IMetricDimensions mDimensions = (IMetricDimensions)box1; // 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()); } } /* Output: Length(in): 30 Width (in): 20 Length(cm): 76.2 Width (cm): 50.8 */ ``` ## 可靠编程如果希望默认度量采用英制单位，请正常实现 Length 和 Width 这两个方法，并从 IMetricDimensions 接口显式实现 Length 和 Width 方法： ``` // Normal implementation: public float Length() { return lengthInches; } public float Width() { return widthInches; } // Explicit implementation: float IMetricDimensions.Length() { return lengthInches * 2.54f; } float IMetricDimensions.Width() { return widthInches * 2.54f; } ``` 这种情况下，可以从类实例访问英制单位，而从接口实例访问公制单位： ``` public static void Test() { Box box1 = new Box(30.0f, 20.0f); IMetricDimensions mDimensions = (IMetricDimensions)box1; System.Console.WriteLine("Length(in): {0}", box1.Length()); System.Console.WriteLine("Width (in): {0}", box1.Width()); System.Console.WriteLine("Length(cm): {0}", mDimensions.Length()); System.Console.WriteLine("Width (cm): {0}", mDimensions.Width()); } ``` ## 请参阅 [C# 编程指南](https://msdn.microsoft.com/zh-CN/library/67ef8sbd.aspx) [类和结构（C# 编程指南）](https://msdn.microsoft.com/zh-CN/library/ms173109.aspx) [接口（C# 编程指南）](https://msdn.microsoft.com/zh-CN/library/ms173156.aspx) [如何：显式实现接口成员（C# 编程指南）](https://msdn.microsoft.com/zh-CN/library/44a9ty12.aspx)