Visual CSharp 1002005 A Developers Notebook [Electronic resources] نسخه متنی

1.11. Limit Access Within Properties

It is now possible to restrict the accessibility
level of the get and set
accessors within a property using access modifiers. Usually you would
restrict access to the set accessor and make the
get accessor public.

Note: Now you can restrict the accessibility level of the get and
set accessors within a property.

1.11.1. How do I do that?

Add the access modifier to either the get or the
set accessor within the property, as illustrated
in Example 1-9.

Example 1-9. Limiting access to property accessors

#region Using directives
using System;
using System.Collections.Generic;
using System.Text;
#endregion
namespace LimitPropertyAccess
{
public class Employee
{
private string name;
public Employee(string name)
{
this.name = name;
}
public string Name
{
get { return name; }
protected set { name = value; }
}
public virtual void ChangeName(string name)
{
// do work here to update many records
Name = name; // access the private accessor
}
}
class Program
{
static void Main(string[  ] args)
{
Employee joe = new Employee("Joe");
// other work here
string whatName = joe.Name; // works
// joe.Name = "Bob"; // doesn't compile
joe.ChangeName("Bob"); // works
Console.WriteLine("joe's name: {0}", joe.Name);
}
}
}

Output:

joe's name: Bob

1.11.2. What just happened?

The design of your Employee class calls for the
string name to be private. You anticipate that one day
you'll want to move this to a database field, so you
resolve that all access to this field will be through a property,
Name.

Other classes are free to access Name, but you do
not want them to set the name directly. If they are going to change
the name field, they must do so through the
ChangeName virtual method. You anticipate that
derived classes will do different work when an employee changes his
name.

Thus you want to provide access to the set
accessor to this class's methods and to methods of
any class that derives from this class, but not to other classes. You
accomplish this by adding the restricting access modifier
protected to the set accessor:

protected set { name = value; }

1.11.3. What about . . .

...restrictions on using access
modifiers?

You cannot use these modifiers on interfaces or explicit interface
member implementations. You can use them only if both
get and set are included, and
you can use them only on one or the other.

Further, the modifier must restrict access, not broaden it. Thus, you
cannot make the property protected and then use a
modifier to make get public.

1.11.4. Where can I learn more?

You can learn more about properties and access modifiers by reading the MSDN
article on properties at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfPropertiesPG.asp.