从未将struct的列表对象分配给它，并且将始终具有其默认值null

Question

How should I initialize a List of a struct. Struct can be initialized, but by just using my list here it says: Folder is never assigned to and will always have its default value null

private struct directories
        {
            public List<string[]> Folder;
        }



directories d1 = new directories();
d1.Folder.Add(Directory.GetDirectories(path1));

Answer 1

The problem with structs is that their constructor is not guaranteed to run. Eg, when you create an array var array = new directories[10]; . Therefore structs cannot have initializers and explicit parameterless constructors.

In this example I use lazy initialization to ensure the folder list to be initialized.

private struct directories
{
    private List<string[]> _folder;
    public List<string[]> Folder
    {
        get {
            if (_folder == null) {
                _folder = new List<string[]>();
            }
            return _folder;
        }
    }
}

---

But in this case I would simply use the existing DirectoryInfo Class from the System.IO namespace. It does this and much more for you. Don't reinvent the wheel.

DirectoryInfo rootDir = new DirectoryInfo(path1);
DirectoryInfo[] directories = rootDir.GetDirectories("*", SearchOption.AllDirectories);

Both, GetDirectories and GetFiles have overloads allowing you to specify search patterns and whether you want to recurse subdirectories.