class - Exposing Member Objects As Properties or Methods in .NET

Question

In .NET, if a class contains a member that is a class object, should that member be exposed as a property or with a method?

Answer 1

You should use properties for anything that conceptually represents the object's state, so long as its retrieval isn't an expensive enough operation that you should avoid using it repeatedly.

From MSDN:

Class library designers often must decide between implementing a class member as a property or a method. In general, methods represent actions and properties represent data. Use the following guidelines to help you choose between these options.

• Use a property when the member is a logical data member. In the following member declarations, Name is a property because it is a logical member of the class.

  public string Name
  get 
  {
      return name;
  }
  set 
  {
      name = value;
  }
  

• Use a method when:

  • The operation is a conversion, such as Object.ToString.
  • The operation is expensive enough that you want to communicate to the user that they should consider caching the result.
  • Obtaining a property value using the get accessor would have an observable side effect.
  • Calling the member twice in succession produces different results.
  • The order of execution is important. Note that a type's properties should be able to be set and retrieved in any order.
  • The member is static but returns a value that can be changed.

  • The member returns an array. Properties that return arrays can be very misleading. Usually it is necessary to return a copy of the internal array so that the user cannot change internal state. This, coupled with the fact that a user can easily assume it is an indexed property, leads to inefficient code. In the following code example, each call to the Methods property creates a copy of the array. As a result, 2n+1 copies of the array will be created in the following loop.

    Type type = // Get a type.
    for (int i = 0; i < type.Methods.Length; i++)
    {
       if (type.Methods[i].Name.Equals ("text"))
       {
          // Perform some operation.
       }
    }
    

The following example illustrates the correct use of properties and methods.

    class Connection
    {
       // The following three members should be properties
       // because they can be set in any order.
       string DNSName {get{};set{};}
       string UserName {get{};set{};}
       string Password {get{};set{};}

       // The following member should be a method
       // because the order of execution is important.
       // This method cannot be executed until after the 
       // properties have been set.
       bool Execute ();
    }