DragnDrop

Avalonia Dragging Service

A lightweight, cross-platform drag-and-drop interaction service for AvaloniaUI, designed for flexibility and extensibility.
Supports multiple independent or nested instances, complex drop precedence, and custom drag/drop logic via callbacks.

✅ Compatible with Avalonia 11+ and .NET 8.0+

✨ Features

• ✅ Multiple independent instances within the same visual tree
• ✅ Nested instance support with inner precedence resolution
• ✅ Overlap-aware drop target and dragged control resolution, prioritizing deeper controls
• ✅ Custom drag/drop callbacks via attached properties (AllowDrag, AllowDrop)
• ✅ Pointer-aware drag context: includes full PointerEventArgs and dragged control set
• ✅ Dynamic service management via IDisposable pattern
• ✅ XAML/Binding-ready: Easy to integrate via attached properties
• ✅ Cross-platform: Fully compatible with all Avalonia-supported platforms

🛠️ How to Use

1. Mark a container (that inherits from Panel control) as the root of a drag instance

<StackPanel local:DraggingServiceAttached.IsRootOfDraggingInstance="True">

2. Enable Dragging/Dropping on your controls:

<Button Content="Drag me!"
        local:DraggingServiceAttached.AllowDrag="{Binding OnDragCallback}" />

<TextBlock Content="Drop on me!"
        local:DraggingServiceAttached.AllowDrag="{Binding OnDropCallback}" />

3. Implement the callbacks in your ViewModel (better for an MVVM approach) or code-behind:

void OnDragCallback(DraggingServiceCallbackArgs args) {
    // Access dragged controls and pointer info
    var controls = args.DraggedControls;
    var pointer = args.PointerEvent;
    // Logic here
}

void OnDropCallback(DraggingServiceCallbackArgs args) {
    // Access dragged controls and pointer info
    var controls = args.DraggedControls;
    var pointer = args.PointerEvent;
    // Logic here
}

Data can be read via the data-context of the dragged controls/drop targets for a better MVVM approach

4. Dispose the service when no longer needed by setting IsRootOfDraggingInstance property to false on the root control:

    control.SetValue(IsRootOfDraggingInstance, false)

or

    DraggingServiceAttached.SetIsRootOfDraggingInstance(control, false);

Notes:

• The service sets a transparent Background if not present and enables the IsHitTestVisible property for every control used in the service.
• Calling Dispose() on the actual instance will not work. Always set the IsRootOfDraggingInstance Attached Property to dispose the instance.
• Each attached property can be set via XAML or code-behind, allowing for flexible integration.

Roadmap and improvements 🚧:

• Add support for multiple dragged controls at the same time
• Add options to tunneling or bubbling events for overlapped dragged controls or drop targets
• Add support for dynamic visual tree changes
• Add support for async callbacks