how to recursively build treeview in c#

Question

private void enumerateValues(IEnumerator<KeyValuePair<string, object>> iEnumerator, TreeNode parentnode)
{
   if(iEnumerator is IEnumerable)
   {
     // ADD THE KEY
     TreeNode childNode = parentnode.Nodes.Add(iEnumerator.Current.Key);

     enumerateValues(iEnumerator.Current.Value, childNode);
   }
  else
   {
     /// add the value
     TreeNode childNode = parentnode.Nodes.Add(iEnumerator.Current.Value.ToString());
   }
}

I somehow get the following error:

The best overloaded method match for 'WindowsFormsApplication1.Form1.enumerateValues(System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string,object>>, System.Windows.Forms.TreeNode)' has some invalid arguments
Argument '1': cannot convert from 'object' to 'System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string,object>>'

How can i fix it please

Answer 1

What is it what you want to do again? Please state your problem and what you want to accomplish.

Answer 2

The following line is most likely the culprit:

enumerateValues(iEnumerator.Current.Value, childNode);

Because the enumerateValues method accepts a IEnumerator<KeyValuePair<string, object>>, the values of the key-value pairs will always be of type object. Therefore you cannot call the method with iEnumerator.Current.Value, because the value isn't of type IEnumerator<KeyValuePair<string, object>>.

This is exactly what the error message tells you:

Argument '1': cannot convert from 'object' to 'System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string,object>>'

You will have to cast iEnumerator.Current.Value to the correct type first, before you can call the method. You can do this using the as operator.

private void enumerateValues(IEnumerator<KeyValuePair<string, object>> iEnumerator, TreeNode parentnode)
{
  // Loop through the values.
  while (iEnumerator.MoveNext())
  {
    // Try a 'safe' cast of the current value.
    // If the cast fails, childEnumerator will be null.
    var childEnumerator = iEnumerator.Current.Value as IEnumerator<KeyValuePair<string, object>>;

    if (childEnumerator != null)
    {
      TreeNode childNode = parentnode.Nodes.Add(iEnumerator.Current.Key);

      enumerateValues(childEnumerator, childNode);
    }
    else
    {
      TreeNode childNode = parentnode.Nodes.Add(iEnumerator.Current.Value.ToString());
    }
  }
}

I also suggest you use IEnumerable<T> instead of IEnumerator<T>, if you can. It shows the intent of the code more clearly, you won't have to handle the iteration manually and you can use LINQ on it.

private void enumerateValues(IEnumerable<KeyValuePair<string, object>> items, TreeNode parentnode)
{
  foreach (var item in items)
  {
    // Try a 'safe' cast of the current value.
    // If the cast fails, childEnumerator will be null.
    var childEnumerator = item.Value as IEnumerable<KeyValuePair<string, object>>;

    if (childEnumerator != null)
    {
      TreeNode childNode = parentnode.Nodes.Add(item.Key);

      enumerateValues(childEnumerator, childNode);
    }
    else
    {
      TreeNode childNode = parentnode.Nodes.Add(item.Value.ToString());
    }
  }
}