如何转换 ICollection <icollection<int> &gt; 列出<list<int> &gt; 在 C# </list<int></icollection<int>

Question

Is there any way to elegantly do this? All I need to do is store a new variable List<List<int>> with values of another array ICollection<ICollection<int>> , but I can't find any way to do this.

The code:

ICollection<ICollection<int>> mycollection = // instantiate with some numbers
List<List<int>> myList = myCollection;

Answer 1

I have an extension-method for this kind of problem, that first tries to cast the collection into a list to prevent obsolete calls to ToList :

public static List<T> SafeToList<T>(this IEnumerable<T> source)
{
    var list = source as List<T>;
    return list ?? source.ToList();
}

Now you can use the following:

var result = myCollectionOfCollections.Select(x => x.SafeToList()).SafeToList();

If your collections may be arrays and you do not focus on List<T> as outcome of the method you can also use the more generic interface IList<T> instead:

public static IList<T> SafeToList<T>(this IEnumerable<T> source)
{
    var list = source as List<T>;
    var array = source as T[];
    return list ?? array ?? source.ToList();
}

or as one-liner:

public static IList<T> SafeToList<T>(this IEnumerable<T> source)
    => source as List<T> ?? source as T[] ?? (IList<T>) source.ToList();

Answer 2

You can do it with Linq:

ICollection<ICollection<int>> data = ...;        
var converted = data.Select(c => c.ToList()).ToList();