1

I have a function as follow. I need to return two parameters. First the index that is as list and it is done by the function. The other parameter that I need to return is a string str. What would be your best suggestion for these outputs? a list with two different parameters? or what? Please let me know your ideas! Thanks

public List<int> index_selexted(TreeNodeCollection treeView, List<int> list)
{
    List<int, List<string>> output_typ = new List<int, >();
    foreach (TreeNode node in treeView)
    {
        if (node.Checked)
        {
            list.Add(node.Index);
            string str = Regex.Match(node.Text, @" \((.*?)\) ").Groups[1].Value;            
        }
        else
        {
            index_selexted(node.Nodes, list);
        }
    }
    return list;
}
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3
  • I'm afraid I'm finding it hard to understand what you mean. Could you try to clarify your question? A short but complete program demonstrating the problem, with sample input and output, would really help. Note that it doesn't look like this is inherently WinForms specific - you happen to be using a TreeNodeCollection, but any tree type would presumably allow you to show the same problem. Commented Mar 3, 2016 at 9:22
  • Did you consider using parameters with out keyword? They could help you getting two (and more) "returns" from a function. Commented Mar 3, 2016 at 9:22
  • List<int, List<string>> output_typ = new List<int, >(); won't compile. Commented Mar 3, 2016 at 9:44

5 Answers 5

Reset to default
2

Well, since TreeNode.Index is not unique within the entire TreeNodeCollection then Dictionary<int, String> is not a choice, but Dictionary<int, List<String>> will do

//TODO: find a better name for dict
public Dictionary<int, List<String>> index_selexted(
  TreeNodeCollection treeView, 
  Dictionary<int, List<String>> dict == null) { // == null for autocreation

  if (null == treeView)  
    throw new ArgumentNullException("treeView");

  if (null == dict)
    dict = new Dictionary<int, List<String>>();

  foreach (TreeNode node in treeView) 
    if (node.Checked) {
      String match = Regex.Match(node.Text, @" \((.*?)\) ").Groups[1].Value; 

      List<String> list;

      if (dict.TryGetValue(node.Index, out list))  
        list.Add(match);
      else
        dict.Add(node.Index, new List<String>() {match}); 
    }
    else 
      index_selexted(node.Nodes, dict);

  return dict;
}

And so you'll have something like this as an output: index + all matches for it:

  {1, ["abc", "def", "gh"]}
  {3, ["xyz"]}

I've added dict == null in order to make the call easier: 

  // You don't have to pre-create the dictionary
  var myDict = index_selexted(myTreeView.Nodes);
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Comments

1

Use a Tuple

var res = new Tuple<string, List<string>>("string1", new List<string>());
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1 Comment

Thanks for the answer, But please notice that one output is integer and other is string.
0

You could either do 

public class IndexSelectionResult{
    public List<something> Index{get;set;}  
    public String StringResult 
}

and return an instance of that, OR, if you're lazy, you can return a TUPLE: 

public Tuple<List<string>, string>> myFunction(){ /* code */}
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0

I believe you want this:

    public static List<int> index_selexted(TreeNodeCollection treeView, out string str)
    {
        str = null;

        var list = new List<int>();
        var output_typ = new List<int>();

        foreach (TreeNode node in treeView)
        {
            if (node.Checked)
            {
                list.Add(node.Index);
                str = Regex.Match(node.Text, @" \((.*?)\) ").Groups[1].Value;            
            }
            else
            {
                index_selexted(node.Nodes, list);
            }
        }

        return list;
    }

usage as such:

var treeview = sometreeview;
string output;
var result = index_selected(treeview, out output);
Console.WriteLine(output);

instead of using the list in your example (List> output_typ = new List();) consider

using a dictionary: 

var output_typ = new Dictionary<int, List<string>>();

or a list of tuples: 

var output_typ = new List<Tuple<int, List<string>>();

Hope this helps

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0

There are a lot of ways to do this in fact, it depends on your specific use case which one you'd prefer.

Using a class

class MyResult {
    public List<int> MyList { get; set; }
    public string MyString { get; set; }
}

public MyResult index_selected(arg1..., arg2...) {
   return new MyResult {
      MyList = outputList,
      MyString = "outputString"
   }
}

Using a class is my preferred way. Though it may clutter if you have many return types it is by far the most readable solution.

Using a tuple

public Tuple<List<int>, string> index_selected(arg1..., arg2...) {
   return Tuple.Create(outputList, "outputString");
}

My second goto option is a tuple. It is a lot more difficult to determine what the values contained in the tuple represent. But doesn't require creating more classes and is a quick solution (I use it mostly for private methods where readability is not much of a concern).

Using the out keyword

public List<int> index_selected(arg1..., out string resultString) {
   resultString = null;
   /* Doing calculations and such */
   resultString = "
   return outputList;
}

In this case the string passed to the resultString parameter will be replaced by whatever you assign to it in the method (see out keyword). Depending on your use case you may also want to look at the ref keyword.

This approach is rather error prone and is generally not preffered.

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