TreeView

The TreeView is a control that presents hierarchical tree data and allows selection of it.

One example for populating a TreeView can be from a directory on the computer. You can create a TreeView in the MainWindow.axaml file in an Avalonia MVVM project.

<TreeView Items="{Binding Items}" 
	  Width="400" Height="480" 
	  HorizontalAlignment="Left">
	<TreeView.ItemTemplate>
		<TreeDataTemplate ItemsSource="{Binding Subfolders}">
			<TextBlock Text="{Binding strNodeText}"/>
		</TreeDataTemplate>
	</TreeView.ItemTemplate>
</TreeView>

In the MainWindowViewModel.cs you can add this code which will recursively look up all the subfolders and populate the TreeView from Items and Subfolders

public ObservableCollection<Node> Items { get; }
public ObservableCollection<Node> SelectedItems { get; }
public string strFolder { get; set; }

public MainWindowViewModel()
{
    strFolder = @"C:\Users\hooty\Desktop"; // EDIT THIS FOR AN EXISTING FOLDER

    Items = new ObservableCollection<Node>();

    Node rootNode = new Node(strFolder);
    rootNode.Subfolders = GetSubfolders(strFolder);
    
    Items.Add(rootNode);
}

public ObservableCollection<Node> GetSubfolders(string strPath)
{
    ObservableCollection<Node> subfolders = new ObservableCollection<Node>();
    string[] subdirs = Directory.GetDirectories(strPath, "*", SearchOption.TopDirectoryOnly);

    foreach (string dir in subdirs)
    {
        Node thisnode = new Node(dir);

        if (Directory.GetDirectories(dir, "*", SearchOption.TopDirectoryOnly).Length > 0)
        {
            thisnode.Subfolders = new ObservableCollection<Node>();

            thisnode.Subfolders = GetSubfolders(dir);
        }

        subfolders.Add(thisnode);
    }

    return subfolders;
}

public class Node
{
    public ObservableCollection<Node> Subfolders { get; set; }

    public string strNodeText { get; }
    public string strFullPath { get; }

    public Node(string _strFullPath)
    {
        strFullPath = _strFullPath;
        strNodeText = Path.GetFileName(_strFullPath);
    }
}

The example project source can be found at avalonia-treeview-test

Reference

TreeView

Source code

TreeView.cs