Interface Properties (C# Programming Guide)

Properties can be declared on an interface. The following example declares an interface property accessor:

public interface ISampleInterface
{
    // Property declaration:
    string Name
    {
        get;
        set;
    }
}

Interface properties typically don't have a body. The accessors indicate whether the property is read-write, read-only, or write-only. Unlike in classes and structs, declaring the accessors without a body doesn't declare an auto-implemented property. Beginning with C# 8.0, an interface may define a default implementation for members, including properties. Defining a default implementation for a property in an interface is rare because interfaces may not define instance data fields.

Example

In this example, the interface IEmployee has a read-write property, Name, and a read-only property, Counter. The class Employee implements the IEmployee interface and uses these two properties. The program reads the name of a new employee and the current number of employees and displays the employee name and the computed employee number.

You could use the fully qualified name of the property, which references the interface in which the member is declared. For example:

string IEmployee.Name
{
    get { return "Employee Name"; }
    set { }
}

The preceding example demonstrates Explicit Interface Implementation. For example, if the class Employee is implementing two interfaces ICitizen and IEmployee and both interfaces have the Name property, the explicit interface member implementation will be necessary. That is, the following property declaration:

string IEmployee.Name
{
    get { return "Employee Name"; }
    set { }
}

implements the Name property on the IEmployee interface, while the following declaration:

string ICitizen.Name
{
    get { return "Citizen Name"; }
    set { }
}

implements the Name property on the ICitizen interface.

interface IEmployee
{
    string Name
    {
        get;
        set;
    }

    int Counter
    {
        get;
    }
}

public class Employee : IEmployee
{
    public static int numberOfEmployees;

    private string _name;
    public string Name  // read-write instance property
    {
        get => _name;
        set => _name = value;
    }

    private int _counter;
    public int Counter  // read-only instance property
    {
        get => _counter;
    }

    // constructor
    public Employee() => _counter = ++numberOfEmployees;
}
System.Console.Write("Enter number of employees: ");
Employee.numberOfEmployees = int.Parse(System.Console.ReadLine());

Employee e1 = new Employee();
System.Console.Write("Enter the name of the new employee: ");
e1.Name = System.Console.ReadLine();

System.Console.WriteLine("The employee information:");
System.Console.WriteLine("Employee number: {0}", e1.Counter);
System.Console.WriteLine("Employee name: {0}", e1.Name);

210 Hazem Abolrous

Sample output

Enter number of employees: 210
Enter the name of the new employee: Hazem Abolrous
The employee information:
Employee number: 211
Employee name: Hazem Abolrous

See also