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Using the Expand Method of TreeView in UI for .NET MAUI

Updated on Dec 22, 2025

Environment

Version	Control	Author
12.0.0	Telerik UI for .NET MAUI TreeView	Dobrinka Yordanova

Description

I want to use the Expand method of the TreeView for UI for .NET MAUI to programmatically expand specific nodes based on their identity and hierarchy.

This knowledge base article also answers the following questions:

How to programmatically expand nodes in TreeView for UI for .NET MAUI?
How to call Expand method in TreeView for UI for .NET MAUI?
How to expand specific nodes in TreeView using code?

Solution

To expand specific nodes in the TreeView control, follow these steps:

Define a data model for the TreeView items:

public class FileSystemNode : NotifyPropertyChangedBase
{
    private FolderNode parent;
    private string name;

    public FolderNode Parent
    {
        get => this.parent;
        set => this.UpdateValue(ref this.parent, value);
    }

    public string Name
    {
        get => this.name;
        set => this.UpdateValue(ref this.name, value);
    }

    public override string ToString()
    {
        return this.name;
    }
}

public class FolderNode : FileSystemNode
{
    public FolderNode()
    {
        this.Children = new ObservableCollection<FileSystemNode>();
    }

    public IList<FileSystemNode> Children { get; }
}

public class FileNode : FileSystemNode
{
}

Create a ViewModel to manage your data and commands:

public class FileSystemViewModel : NotifyPropertyChangedBase
{
    private const int parentCount = 10;
    private const int childCount = 10;
    private const int fileCount = 10;

    private readonly ObservableCollection<FileSystemNode> fileSystemNodes;
    private FileSystemNode selectedNode;
    private int folderIndex;
    private int fileIndex;

    public FileSystemViewModel()
    {
        this.fileSystemNodes = new ObservableCollection<FileSystemNode>();
        this.InitializeFileSystem();

        Data = CreateData(200);
    }
    public List<int> Data { get; set; }

    internal static List<int> CreateData(int count)
    {
        List<int> source = new List<int>();

        for (int i = 0; i < count; i++)
        {
            source.Add(i);
        }

        return source;
    }
    public FileSystemNode SelectedNode
    {
        get => this.selectedNode;
        set => this.UpdateValue(ref this.selectedNode, value);
    }

    public IList<FileSystemNode> FileSystemNodes => this.fileSystemNodes;

    private void InitializeFileSystem()
    {
        for (int parentIndex = 0; parentIndex < parentCount; parentIndex++)
        {
            var parentFolderNode = this.CreateFolderNode();

            for (int childIndex = 0; childIndex < childCount; childIndex++)
            {
                var childFolderNode = this.CreateFolderNode();

                for (int fileIndex = 0; fileIndex < fileCount; fileIndex++)
                {
                    var childFileNode = this.CreateFileNode();

                    childFileNode.Parent = childFolderNode;
                    childFolderNode.Children.Add(childFileNode);
                }

                childFolderNode.Parent = parentFolderNode;
                parentFolderNode.Children.Add(childFolderNode);
            }

            this.fileSystemNodes.Add(parentFolderNode);
        }
    }

    private FolderNode CreateFolderNode()
    {
        this.folderIndex++;

        return new FolderNode
        {
            Name = $"Folder {this.folderIndex}"
        };
    }

    private FileNode CreateFileNode()
    {
        this.fileIndex++;

        return new FileNode
        {
            Name = $"File {this.fileIndex}"
        };
    }
}

Define the TreeView in XAML with the button for calling the Expand() method:

xml

<Grid RowDefinitions="Auto, *" RowSpacing="5">
    <VerticalStackLayout Grid.Row="0" Spacing="5">
        <HorizontalStackLayout Spacing="5">
            <Button Text="Expand Folder 1 / Folder 2 using Expand method"
                    Clicked="OnExpandClicked" />
        </HorizontalStackLayout>
    </VerticalStackLayout>
    <telerik:RadTreeView x:Name="treeView"
                         Grid.Row="1"
                         ItemsSource="{Binding FileSystemNodes}"
                         SelectedItem="{Binding SelectedNode, Mode=TwoWay}">
        <telerik:TreeViewDescriptor TargetType="{x:Type local:FolderNode}"
                                    IdentityMemberPath="Name"
                                    DisplayMemberPath="Name"
                                    ItemsSourcePath="Children" />
        <telerik:TreeViewDescriptor TargetType="{x:Type local:FileNode}"
                                    IdentityMemberPath="Name"
                                    DisplayMemberPath="Name" />
    </telerik:RadTreeView>
</Grid>

Define the OnExpandClicked method in the code-behind and call the RadTreeView.Expand() method. In the method pass the item path of the nodes to expand.

csharp

private void OnExpandClicked(object sender, EventArgs e)
{
    if (this.BindingContext is not FileSystemViewModel vm)
    {
        return;
    }

    // Find the parent node named "Folder 1" and its child node "Folder 2"
    var parent = vm.FileSystemNodes
        .OfType<FolderNode>()
        .FirstOrDefault(p => p.Name == "Folder 1");

    var child = parent?
        .Children
        .OfType<FolderNode>()
        .FirstOrDefault(c => c.Name == "Folder 2");

    if (parent is not null && child is not null)
    {
        var itemPath = new object[] { parent.Name, child.Name };
        this.treeView.Expand(itemPath); // Expand the node using the item path
    }
}

Using the Expand Method of TreeView in UI for .NET MAUI

Environment

Description

Solution

See Also