c# - 将列表< Guid > 转换为列表< Guid? >

Question

将 List< Guid > 转换为 List< Guid 的最佳做法是什么？>

以下不编译：

public List<Guid?> foo()
{
    List<Guid> guids = getGuidsList();
    return guids; 
}

Answer 1

这个问题似乎改变了几次，所以我会以两种方式展示转换：

转换List<Guid?>为List<Guid>：

var guids = nullableGuids.OfType<Guid>().ToList();
// note that OfType() implicitly filters out the null values,
// a Cast() would throw a NullReferenceException if there are any null values

转换List<Guid>为List<Guid?>：

var nullableGuids = guids.Cast<Guid?>().ToList();

Answer 2

public List<Guid> foo()
{
    return  foo.Where(x=>x != null).Cast<Guid>().ToList();
}

Answer 3

像这样的东西

return guids.Select(e => new Guid?(e)).ToList();

Answer 4

public List<Guid?> foo()
{
    List<Guid> source = getGuidsList();
    return  source.Select(x => new Guid?(x)).ToList();

}

Answer 5

略有不同的做法：

public List<Guid> foo()
{
    return foo.Where(g => g.HasValue).Select(g => g.Value).ToList();
}