How to: Explicitly Implement Members of Two Interfaces (C# Programming Guide)

Explicit interface implementation also allows the programmer to implement two interfaces that have the same member names and give each interface member a separate implementation. This example displays the dimensions of a box in both metric and English units. The Box class implements two interfaces IEnglishDimensions and IMetricDimensions, which represent the different measurement systems. Both interfaces have identical member names, Length and Width.

Example

// 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
*/

Robust Programming

If you want to make the default measurements in English units, implement the methods Length and Width normally, and explicitly implement the Length and Width methods from the IMetricDimensions interface:

// 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;
}

In this case, you can access the English units from the class instance and access the metric units from the interface instance:

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());
}

See Also

Tasks

How to: Explicitly Implement Interface Members (C# Programming Guide)

Concepts

C# Programming Guide

Reference

Classes and Structs (C# Programming Guide)

Interfaces (C# Programming Guide)