C＃：在单例模式中仅初始化Random（）一次

Question

I am trying to initialize only once a random variable, let's say 'rnd'. So If from many points of my program it is called, then the random variable will not be initialized again, only first time.

So I have created a singleton but I do not know how to call only once Random().

public sealed class Randomize
{
    private static Randomize instance = null;
    private static readonly object padlock = new object();

    Randomize()
    {
    }
    public static Randomize Instance
    {
        get
        {
            lock (padlock)
            {
                if (instance == null)
                {
                    instance = new Randomize();
                }
                return instance;
            }
        }
    }
}

Within this class I would like to create a private readonly random variable, 'rnd', which is initialized only once, the first time, to:

Random rnd = new Random()

Then, I would like to create a property to read its value, for example:

        public Random Rnd
        {
            get { return rnd; }
        }

I do not want to allow to change its value because it is assigned first time only, so I only want the property to be readonly (get), not set.

So from many points of my program I can do:

private readonly Random rnd;
Random rnd = Randomize.Instance.Rnd;

But each time I call it using above expression I do not want to initizalize random variable again (by doing new Random()) instead I want to always obtain the same value it was rnd variable was initialized for first time.

Any ideas on how to do it?

Answer 1

Just use a static constructor, by definition that is gaurenteed to only be called once

The MSDN Documentation States :

A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced.

public sealed class Randomize
{
    private static Randomize instance = null;
    private static readonly object padlock = new object();

    public Random GetRandom { get { return rnd; } }        

    private static readonly Random rnd;

    static Randomize()
    {
        rnd = new Random();
    }
}

Answer 2

You can access Randomize.Random with the following snippet and it will always return the once-initialized Random rnd field.

public sealed class Randomize {
    private static readonly Random rnd = new Random();
    public static Random Random {
       get {
           return rnd;
       }
    }
}

Answer 3

Read only variables can be assigned in the constructor, so I would go that route.

public sealed class Randomize {
    /* access level here */ Random rnd { get { return r; } }
    private readonly Random r;

    static Randomize() {
        r = new Random();
    }
}

// or

        private readonly Random r = new Random();
        public Random rnd {
            get {
                return r;
            }
        }