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How to explicitly implement interface members (C# Programming Guide)

  • Article

This example declares an interface, IDimensions, and a class, Box, which explicitly implements the interface members GetLength and GetWidth. The members are accessed through the interface instance dimensions.

Example

interface IDimensions
{
    float GetLength();
    float GetWidth();
}

class Box : IDimensions
{
    float lengthInches;
    float widthInches;

    Box(float length, float width)
    {
        lengthInches = length;
        widthInches = width;
    }
    // Explicit interface member implementation:
    float IDimensions.GetLength()
    {
        return lengthInches;
    }
    // Explicit interface member implementation:
    float IDimensions.GetWidth()
    {
        return widthInches;
    }

    static void Main()
    {
        // Declare a class instance box1:
        Box box1 = new Box(30.0f, 20.0f);

        // Declare an interface instance dimensions:
        IDimensions dimensions = box1;

        // 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}", box1.GetLength());
        //System.Console.WriteLine("Width: {0}", box1.GetWidth());

        // Print out the dimensions of the box by calling the methods
        // from an instance of the interface:
        System.Console.WriteLine("Length: {0}", dimensions.GetLength());
        System.Console.WriteLine("Width: {0}", dimensions.GetWidth());
    }
}
/* Output:
    Length: 30
    Width: 20
*/

Robust Programming

  • Notice that the following lines, in the Main method, are commented out because they would produce compilation errors. An interface member that is explicitly implemented cannot be accessed from a class instance:

    //System.Console.WriteLine("Length: {0}", box1.GetLength());
//System.Console.WriteLine("Width: {0}", box1.GetWidth());

  • Notice also that the following lines, in the Main method, successfully print out the dimensions of the box because the methods are being called from an instance of the interface:

    System.Console.WriteLine("Length: {0}", dimensions.GetLength());
System.Console.WriteLine("Width: {0}", dimensions.GetWidth());

See also