如何：顯式實現兩個接口的成員（C# 編程指南） · MSDN C# 編程指南 & 參考手冊 2015

# 如何：顯式實現兩個接口的成員（C# 編程指南）顯式[接口](https://msdn.microsoft.com/zh-CN/library/87d83y5b.aspx)實現還允許程序員實現具有相同成員名稱的兩個接口，并為每個接口成員各提供一個實現。本示例同時以公制單位和英制單位顯示框的尺寸。Box [類](https://msdn.microsoft.com/zh-CN/library/0b0thckt.aspx)實現 IEnglishDimensions 和 IMetricDimensions 兩個接口，它們表示不同的度量系統。兩個接口有相同的成員名稱 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 */ ``` ## 可靠編程如果希望默認度量采用英制單位，請正常實現 Length 和 Width 這兩個方法，并從 IMetricDimensions 接口顯式實現 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; } ``` 這種情況下，可以從類實例訪問英制單位，而從接口實例訪問公制單位： ``` 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()); } ``` ## 請參閱 [C# 編程指南](https://msdn.microsoft.com/zh-CN/library/67ef8sbd.aspx) [類和結構（C# 編程指南）](https://msdn.microsoft.com/zh-CN/library/ms173109.aspx) [接口（C# 編程指南）](https://msdn.microsoft.com/zh-CN/library/ms173156.aspx) [如何：顯式實現接口成員（C# 編程指南）](https://msdn.microsoft.com/zh-CN/library/44a9ty12.aspx)