Question

I am creating a program that cursively finds all the files and directories in the specified path. So one node may have other nodes if that node happens to be a directory.

Here is my Node class:

class Node
{
    public List<Node> Children = new List<Node>(); // if node is directory then children will be the files and directories in this direcotry
    public FileSystemInfo Value { get; set; }  // can eather be a FileInfo or DirectoryInfo

    public bool IsDirectory 
    { 
        get{ return Value is DirectoryInfo;} 
    }

    public long Size   // HERE IS WHERE I AM HAVING PROBLEMS! I NEED TO RETRIEVE THE 
    {                  // SIZE OF DIRECTORIES AS WELL AS FOR FILES.
        get
        {
            long sum = 0;

            if (Value is FileInfo)
                sum += ((FileInfo)Value).Length;
            else
                sum += Children.Sum(x => x.Size);

            return sum;
        }
    }

    // this is the method I use to filter results in the tree
    public Node Search(Func<Node, bool> predicate)
    {
         // if node is a leaf
         if(this.Children.Count==0)
         {
             if (predicate(this))
                return this;
             else
                return null;
         }
         else // Otherwise if node is not a leaf
         {
             var results = Children.Select(i => i.Search(predicate)).Where(i => i != null).ToList();

             if (results.Any()) // THIS IS HOW REMOVE AND RECUNSTRUCT THE TREE WITH A FILTER
             {
                var result = (Node)MemberwiseClone();
                result.Children = results;
                return result;
             }
             return null;
         }             
    }

}

and thanks to that node class I am able to display the tree as:

In one column I display the name of the directory or file and on the right the size. The size is formated as currency just because the commas help visualize it more clearly.

So now my problem is The reason why I have this program was to perform some advance searches. So I may only want to search for files that have the “.txt” extension for example. If I perform that filter on my tree I will get:

(note that I compile the text to a function that takes a Node and returns a bool and I pass that method to the Search method on my Node class in order to filter results. More information on how to dynamically compile code can be found at: http://www.codeproject.com/Articles/10324/Compiling-code-during-runtime) Anyways that has nothing to do with this question. The important part was that I removed all the nodes that did not matched that criteria and because I removed those nodes now the sizes of the directories changed!!!

So my question is how will I be able to filter results maintaining the real size of the directory. I guess I will have to remove the property Size and replace it with a field. The problem with that is that every time I add to the tree I will have to update the size of all the parent directories and that gets complex. Before starting coding it that way I will appreciate your opinion on how I should start implementing the class.

Answer 1

Since you’re using recursion and your weight is a node-level property you can’t expect that will continue to sum even after you remove the node. You either promote it to a upper level (collection) or use an external counter within the recursion (which counts but not depending on filter, you’ll need to carry this through the recuersion).

Anyway, why are you implementing a core .NET functionality again? any reason beyond filtering or recursive search? both are pretty well implemented in the BCL.