C# Cookbook

3.21. Preventing the Creation of an Only Partially Initialized Object

Problem

You need to force a client to use an overloaded constructor, which accepts parameters to fully initialize the object, rather than a default constructor, which may not fully initialize the object. Often a default constructor cannot fully initialize an object since it may not have the necessary information to do it. Using a default constructor, the client is required to perform a multistep process; for instance, create the object and then initialize its fields either through various properties and/or methods.

Solution

By removing the default constructor and strictly using parameterized constructors, the client is forced to provide the necessary initialization parameters during object creation. The following Log class will not initialize its LogStream field to a StreamWriter object on construction:

public class Log
{
    private StreamWriter logStream = null;

    public StreamWriter LogStream
    {
        get {return (logStream);}
        set {logStream = value;}
    }

    // use the LogStream field...
    public void Write(string text)
    {
        logStream.Write(text);
    }
}

The C# compiler will automatically create a default constructor that calls the default constructor of its base class, if you omit the constructor for a class. The following modified class will prevent the default constructor from being created:

public class Log
{
    public Log(StreamWriter logStream)
               {
               this.logStream = logStream;
               } private StreamWriter logStream = null; public StreamWriter ...