如何:使用继承显式实现接口成员(C# 编程指南) - C# 编程指南

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如何:使用继承显式实现接口成员(C# 编程指南)

发布于 2019-11-12 字数3486 浏览 841 评论 0

显式接口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。

示例

C#  复制代码
// 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:

C#  复制代码
// 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:

C#  复制代码
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());
}

请参见

任务

如何:显式实现接口成员(C# 编程指南)

概念

C# 编程指南

参考

类和结构(C# 编程指南)接口(C# 编程指南)

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