// 1. Install NuGet packages
// Install-Package Syncfusion.Blazor.Navigations -Version 26.1.35
// Install-Package Syncfusion.Blazor.Themes -Version 26.1.35

// 2. Add to _Imports.razor
@using Syncfusion.Blazor
@using Syncfusion.Blazor.Navigations

// 3. Register service in Program.cs
builder.Services.AddSyncfusionBlazor();

// 4. Add CSS theme to Index.html or _Layout.cshtml
<link href="_content/Syncfusion.Blazor.Themes/bootstrap5.css" rel="stylesheet" />

@using Syncfusion.Blazor.Navigations

<SfTreeView TValue="MailItem">
    <TreeViewFieldsSettings TValue="MailItem"
        Id="Id"
        Text="FolderName"
        Child="Children"
        DataSource="@MyFolder">
    </TreeViewFieldsSettings>
    <TreeViewEvents TValue="MailItem" NodeSelected="OnNodeSelected"></TreeViewEvents>
</SfTreeView>

@code {
    public class MailItem
    {
        public string? Id { get; set; }
        public string? FolderName { get; set; }
        public List<MailItem>? Children { get; set; }
    }

    void OnNodeSelected(NodeSelectEventArgs args)
    {
        Console.WriteLine($"Selected: {args.NodeData.Text}");
    }

    List<MailItem> MyFolder = new()
    {
        new MailItem { Id = "1", FolderName = "Inbox", Children = new() },
        new MailItem { Id = "2", FolderName = "Sent", Children = new() }
    };
}

<SfTreeView TValue="Item" @bind-SelectedNodes="@SelectedIds">
    <TreeViewFieldsSettings TValue="Item" DataSource="@Items" />
    <TreeViewEvents TValue="Item" NodeSelected="OnSelect"></TreeViewEvents>
</SfTreeView>

@code {
    string[] SelectedIds = Array.Empty<string>();
    void OnSelect(NodeSelectEventArgs args) => Console.WriteLine(args.NodeData.Text);
}

<SfTreeView TValue="Item" AllowMultiSelection="true" @bind-SelectedNodes="@SelectedIds">
    <TreeViewFieldsSettings TValue="Item" DataSource="@Items" />
</SfTreeView>

void OnNodeExpanded(NodeExpandEventArgs args)
{
    if (args.NodeData.HasChild && args.NodeData.Child == null)
    {
        // Load children from API
        args.NodeData.Child = await FetchChildren(args.NodeData.Id);
    }
}

<SfTreeView TValue="Item" AllowDragAndDrop="true">
    <TreeViewFieldsSettings TValue="Item" DataSource="@Items" />
    <TreeViewEvents TValue="Item" NodeDropped="OnDropped"></TreeViewEvents>
</SfTreeView>

void OnDropped(DragAndDropEventArgs args) => UpdateHierarchy(args);

<SfTreeView TValue="Item" AllowEditing="true" DoubleClickAction="DoubleClickAction.Edit">
    <TreeViewFieldsSettings TValue="Item" DataSource="@Items" />
    <TreeViewEvents TValue="Item" NodeEdited="OnEdited"></TreeViewEvents>
</SfTreeView>

void OnEdited(NodeEditEventArgs args) => SaveChanges(args.NodeData);

<SfTreeView TValue="Item" AllowCheckBoxes="true" ChildChecking="ChildCheckState.Both">
    <TreeViewFieldsSettings TValue="Item" DataSource="@Items" />
</SfTreeView>

var checked = treeRef.GetAllCheckedNodes();