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How to declare and use read write properties (C# Programming Guide)

  • Article

Properties provide the convenience of public data members without the risks that come with unprotected, uncontrolled, and unverified access to an object's data. Properties declare accessors: special methods that assign and retrieve values from the underlying data member. The set accessor enables data members to be assigned, and the get accessor retrieves data member values.

This sample shows a Person class that has two properties: Name (string) and Age (int). Both properties provide get and set accessors, so they're considered read/write properties.

Example

class Person
{
    private string _name = "N/A";
    private int _age = 0;

    // Declare a Name property of type string:
    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            _name = value;
        }
    }

    // Declare an Age property of type int:
    public int Age
    {
        get
        {
            return _age;
        }

        set
        {
            _age = value;
        }
    }

    public override string ToString()
    {
        return "Name = " + Name + ", Age = " + Age;
    }
}

public class Wrapper
{
    private string _name = "N/A";
    public string Name
    {
        get
        {
            return _name;
        }
        private set
        {
            _name = value;
        }
    }

}

class TestPerson
{
    static void Main()
    {
        // Create a new Person object:
        Person person = new Person();

        // Print out the name and the age associated with the person:
        Console.WriteLine("Person details - {0}", person);

        // Set some values on the person object:
        person.Name = "Joe";
        person.Age = 99;
        Console.WriteLine("Person details - {0}", person);

        // Increment the Age property:
        person.Age += 1;
        Console.WriteLine("Person details - {0}", person);

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }
}
/* Output:
    Person details - Name = N/A, Age = 0
    Person details - Name = Joe, Age = 99
    Person details - Name = Joe, Age = 100
*/

Robust Programming

In the previous example, the Name and Age properties are public and include both a get and a set accessor. Public accessors allow any object to read and write these properties. It's sometimes desirable, however, to exclude one of the accessors. You can omit the set accessor to make the property read-only:

public string Name
{
    get
    {
        return _name;
    }
    private set
    {
        _name = value;
    }
}

Alternatively, you can expose one accessor publicly but make the other private or protected. For more information, see Asymmetric Accessor Accessibility.

Once the properties are declared, they can be used as fields of the class. Properties allow for a natural syntax when both getting and setting the value of a property, as in the following statements:

person.Name = "Joe";
person.Age = 99;

In a property set method a special value variable is available. This variable contains the value that the user specified, for example:

_name = value;

Notice the clean syntax for incrementing the Age property on a Person object:

person.Age += 1;

If separate set and get methods were used to model properties, the equivalent code might look like this:

person.SetAge(person.GetAge() + 1);

The ToString method is overridden in this example:

public override string ToString()
{
    return "Name = " + Name + ", Age = " + Age;
}

Notice that ToString isn't explicitly used in the program. It's invoked by default by the WriteLine calls.

See also