如何在扩展方法中实现C＃随机播放算法？

Question

I have a list that looks like this:

IList<TQBase> hs;

public class TQBase
{
    public int i { get; set; }
    public int q { get; set; }
}

I would like to shuffle this list and I found this method:

public static void Shuffle<T>(this IList<T> list)  
{  
    Random rng = new Random();  
    int n = list.Count;  
    while (n > 1) {  
        n--;  
        int k = rng.Next(n + 1);  
        T value = list[k];  
        list[k] = list[n];  
        list[n] = value;  
    }  
}

I am trying to use it like this:

 IList<TQBase> tqhb // This is populated from the repository in an earlier statement

 var abc = tqhb.Shuffle<TQBase>();

It's giving me an error pointing to abc and saying:

 Cannot assign void to an implicitly-typed local variable   

Is there a problem with the way I am trying to do the shuffle ?

Answer 1

A very easy way to shuffle:

hs.OrderBy(a => Guid.NewGuid()).ToList();

For simple shuffling purposes a Guid is random enough. Create a Guid for each entry and order by it, it will end up as a shuffled list.

I realize it doesn't solve the problem in your extension, but others have already covered it. It seems like you were looking for a shuffle mechanism and not this one in particular so I provided an easy-to-use alternative.

Answer 2

You are trying to assign a new variable a value when your extension method returns type void . Use it like this:

tqhb.Shuffle<TQBase>();

Answer 3

The extension method shuffles the list inline, you don't have to assign the return to anything (Hence why the return type is void !).

tqhb.Shuffle<TQBase>();

Also, the compiler should be smart enough to figure out the generic type of the method so you should just be able to call

tqhb.Shuffle();

Answer 4

There's an error in your Extension method:

public static IList<T> Shuffle<T>(this IList<T> list)  
{  
    Random rng = new Random();  
    int n = list.Count;  
    while (n > 1) {  
        n--;  
        int k = rng.Next(n + 1);  
        T value = list[k];  
        list[k] = list[n];  
        list[n] = value;  
    } 
    return list; 
}

Or, you use it without assignment:

tqhb.Shuffle<TQBase>();

After tqhb will be different.