Recursion in the constructor

Question

Please review the following code snippet. I get a nullreferenceexception in "this.directories.Add (new directory (s))". Recursion seems to work as long as it doesn't “unwind”, at which point “new directory (s)” seems to be null. I'm not sure why it behaves this way, I thought there might be special rules, because recursion is in the constructor. Please, help.

namespace AnalyzeDir { class directory { public string[] files; public ArrayList directories; public string mypath; public string myname; public directory(string mp) { mypath = mp; myname = mypath.Substring(mypath.LastIndexOf("\\")); files = Directory.GetFiles(mypath); fillDirectoriesRescursive(); } public void fillDirectoriesRescursive() { string[] dirpaths = Directory.GetDirectories(mypath); if (dirpaths != null && (dirpaths.Length > 0)) { foreach(string s in dirpaths) { this.directories.Add(new directory(s)); } } } 

Answer 1

You did not initialize directories to be anything.

I would suggest not to do this in the constructor, but instead move it to a method call. It goes back to "implied behavior" where you should not have complex external system logic inside accessory properties.

You are also using the very old ArrayList construct. Instead, I suggest using ICollection<directory> . More type safety and all that.

Answer 2

You did not initialize directories at all.