Why Static method sometimes returns same result for separate call?

Question

In my c# code I have a static method. Here is the code sample:

public class RandomKey
{
    public static string GetKey()
    {
        Random rng = new Random();
        char[] chars = new char[8];
        for (int i = 0; i < chars.Length; i++)
        {
            int v = rng.Next(10 + 26 + 26);
            char c;
            if (v < 10)
            {
                c = (char)('0' + v);
            }
            else if (v < 36)
            {
                c = (char)('a' - 10 + v);
            }
            else
            {
                c = (char)('A' - 36 + v);
            }
            chars[i] = c;
        }

        string key = new string(chars);
        key += DateTime.Now.Ticks.ToString();
        return key;
    }
}

I am calling this function from another Class's method.

Class SomeClass
{
    Void SomeMethod()
    {
        for(int i=0; i<100; i++)
        {
            System.Diagnostics.Debug.WriteLine(i + "===>" + RandomKey.GetKey());
        }
    }
}

But now the problem is sometimes I am getting the same output from the static method though the function was called separately. Is there any wrong with my code?

Answer 1

The reason is that you are initializing the Random object inside the method.
When you call the method in close time proximity (like inside a loop), the Random object is initialized with the same seed. (see Matthew Watson's comment to find out why.)
To prevent that you should declare and initialize the Random object as a static field, like this:

public class RandomKey
{
    static Random rng = new Random();

    public static string GetKey() 
    {
    // do your stuff...
    }
}

Answer 2

You keep reinitializing the Random value. Move that out to a static field. Also you can format numbers in hex using ToString with a formatter.

Also, DateTime.Now is a bad idea. See this answer for a better way to allocate unique, timestamp values.