Question

I want to organize a set of Object (MyPlugin) in a TreeView by Category.
Actually i’m adding them to the TreeView using the following method :

  internal static TreeNode AddPluginNode(TreeView parent, AbstractEnvChecker plugin)
  {
      TreeNode created = new TreeNode(plugin.Name) { Tag = plugin };
      parent.Nodes.Add(created);
      return created;
  }

// I’m using the Tag so i can conserve the MyPlugin Type for each Node

And this is the method i’m using to populate my TreeView from a List<MyPlugin> :

internal static void FillTreeViewWithPlugins(TreeView p_TreeView, Type p_Type, IList<AbstractEnvChecker> p_List)
{
    TreeNode v_TreeNode;
    if (p_TreeView != null)
    {
        p_TreeView.Nodes.Clear();
        foreach (object p_Item in p_List)
        {
            if (p_Item.GetType().IsSubclassOf(p_Type))
            {
                v_TreeNode = null;
                v_TreeNode = AddPluginNode(p_TreeView, p_Item as AbstractEnvChecker);

            }
        }
    }
}

Everything works well, but the problem is that the previous method displays a simple TreeView that contains then list of MyPlugin. I want to classify them by a property called Category (String MyPlugin.Category).

So i should proceed like this :

TreeNode testNodeA = new TreeNode("A"); 
TreeNode testNodeB = new TreeNode("B");
TreeNode testNodeC = new TreeNode("C");
TreeNode[] array = new TreeNode[] { testNodeA, testNodeB, testNodeC };
TreeNode cat = new TreeNode("Categorie X", array);
treeView1.Nodes.Add(cat);

1. If i want to keep my previous code, i cannot know how many plugins will i add to each category so i cannot use an Array with fixed dimensions …
2. I can’t use List because the TreeNode constructor accepts only Array and the TreeView.Nodes.Add method accepts only TreeNode …

How can i do it ?

Answer 1

Build a dictionary of categories on the fly while creating the nodes. Later, add only these nodes to the tree. The steps are as follows:

Declare a dictionary like that

Dictionary<string, TreeNode> categoryNodes = new ...;

The key is the category name, the value is the TreeNode for the category.

While iterating over all the MyPlugins in your list, check whether there’s a category node in the dictionary and create one if there’s not:

if (!categoryNodes.ContainsKey(p_Item.Category))
    categoryNodes[p_Item.Category] = new TreeNode(p_Item.Category);

Add the new TreeNode for the plugin under the respective category node:

v_TreeNode = AddPluginNode(categoryNodes[p_Item.Category], p_Item as AbstractEnvChecker);

In the end, add all the values of the dictionary to the tree:

foreach (string key in categoryNodes.Keys)
{
    p_TreeView.Nodes.Add(categoryNodes[key]);
}

Your code should look like this:

internal static void FillTreeViewWithPlugins(TreeView p_TreeView, Type p_Type, IList<AbstractEnvChecker> p_List)
{
    Dictionary<string, TreeNode> categoryNodes = new Dictionary<string, TreeNode>();
    TreeNode v_TreeNode;

    if (p_TreeView != null)
    {
        p_TreeView.Nodes.Clear();

        foreach (object p_Item in p_List)
        {
            if (p_Item.GetType().IsSubclassOf(p_Type))
            {
                if (!categoryNodes.ContainsKey(p_Item.Category))
                    categoryNodes[p_Item.Category] = new TreeNode(p_Item.Category);

                v_TreeNode = null;
                v_TreeNode = AddPluginNode(categoryNodes[p_Item.Category], p_Item as AbstractEnvChecker);    
            }
        }

        foreach (string cat in categoryNodes.Keys)
            p_TreeView.Nodes.Add(categoryNodes[cat]);
    }
}