C# – MVVM with TreeView – add nodes

Kent wrote an interesting blog about this topic: View Models: POCOs versus DependencyObjects.

Short summary:

1. DependencyObjects are not marked as serializable
2. The DependencyObject class overrides and seals the Equals() and GetHashCode() methods
3. A DependencyObject has thread affinity – it can only be accessed on the thread on which it was created

I prefer the POCO approach. A base class for PresentationModel (aka ViewModel) which implements INotifyPropertyChanged interface can be found here: http://compositeextensions.codeplex.com

It's not that bad, but you forgot to call treeView2.EndUpdate() in your addParentNode_Click() method.
You can also call treeView2.ExpandAll() at the end of your addChildNode_Click() method to see your child node directly.

private void addParentNode_Click(object sender, EventArgs e) {
  treeView2.BeginUpdate();
  //treeView2.Nodes.Clear();
  string yourParentNode;
  yourParentNode = textBox1.Text.Trim();
  treeView2.Nodes.Add(yourParentNode);
  treeView2.EndUpdate();
}

private void addChildNode_Click(object sender, EventArgs e) {
  if (treeView2.SelectedNode != null) {
    string yourChildNode;
    yourChildNode = textBox1.Text.Trim();
    treeView2.SelectedNode.Nodes.Add(yourChildNode);
    treeView2.ExpandAll();
  }
}

I don't know if it was a mistake or not but there was 2 TreeViews. I changed it to only 1 TreeView...

EDIT: Answer to the additional question:
You can declare the variable holding the child node name outside of the if clause:

private void addChildNode_Click(object sender, EventArgs e) {
  var childNode = textBox1.Text.Trim();
  if (!string.IsNullOrEmpty(childNode)) {
    TreeNode parentNode = treeView2.SelectedNode ?? treeView2.Nodes[0];
    if (parentNode != null) {
      parentNode.Nodes.Add(childNode);
      treeView2.ExpandAll();
    }
  }
}

Note: see http://www.yoda.arachsys.com/csharp/csharp2/nullable.html for info about the ?? operator.