Godot - Drag and drop example in GDScript and C#

Slot.cs

/**
 * Handle input events on the current slot.
 * 
 * @param InputEvent @event The input event to handle
 * 
 * @return void
 */
public override void _GuiInput(InputEvent @event)
{
    // If right click, then equip item
    if (@event.IsActionReleased("right_click")) {
        this.AcceptEvent();
        var item = this.getItem();

        if (item != null) {
            this.unsetItem();
            var parent = (BagContent) this.GetParent();
            parent.emitEquip(item);
        }
    }

    // If left click, force drag and drop
    if (@event.IsActionReleased("left_click")) {
        GD.print("ACTION RELEASED!");
        this.AcceptEvent();
        var item = this.getItem();

        if (item != null) {
            this.unsetItem();
            var preview = this.getDragPreview(item);
            this.ForceDrag(item, preview);
        }
    }
}


/**
 * Returns the drag-and-drop preview for an item.
 * 
 * @return Control | null
 */
public Control getDragPreview(Item item = null)
{
    if (item == null) {
        item = this.getItem();
    }

    if (item != null) {
        var preview = new Control();
        var sprite = new Sprite();
        sprite.SetTexture(item.getIcon());
        preview.AddChild(sprite);

        return preview;
    }

    return null;
}

/**
 * Unsets the current item and starts the drag-and-drop flow.
 * 
 * @param Vector2 _pos  The position clicked
 * 
 * @return Item		    The item we want to drag
 */
public override Godot.Object GetDragData(Vector2 position)
{
    var item = this.getItem();
    var preview = this.getDragPreview();
    this.SetDragPreview(preview);
    this.unsetItem();

    return item;
}

/**
 * Checks whether we can drop the item on the current slot.
 * If the item is of class Item, then return true. Else return false
 * 
 * @param Vector2 position  The position clicked
 * @param Variant data      The dropped data
 * 
 * @return bool			    True if we can drop the item here, false otherwise
 */
public override bool CanDropData(Vector2 position, object item)
{
    if (item is Item) {
        return true;
    }
    return false;
}


/**
 * Drop an item on the current slot. If the slot is already occupied, swap them.
 * 
 * @param Vector2 position  The click/drop position
 * @param Item	  item	    The item to drop
 * 
 * @return void
 */
public override void DropData(Vector2 position, object item)
{
    if (Input.IsActionPressed("left_click")) {
        this.CallDeferred("force_drag", (Item)item, this.getDragPreview((Item)item));
    } else {
        var oldItem = this.getItem();
        if (oldItem == null) {
            this.setItem((Item)item);
        } else {
            this.EmitSignal("swapItem", item);
        }
    }
}


/**
 * Swaps the item currently occupying the slot with another one, and forces drag-and-drop on the current one
 *  
 * @param Item item	The item which to swap with the one currently on the slot
 * 
 * @return void
 */
public void swapItem(Item item)
{
    var oldItem = this.getItem();
    this.unsetItem();
    this.setItem(item);
    var preview = this.getDragPreview(oldItem);
    this.CallDeferred("force_drag", oldItem, preview);
}

Slot.gd

"""
	Handle input events on the current slot.
	
	@param InputEvent	ev	The input event to handle
"""
func _gui_input(ev):
	"""
		If right click, then equip item
	"""
	if (ev.is_action_pressed("right_click")):
		self.accept_event()
		var item = self.getItem()
		
		if(item != null):
			self.unsetItem()
			get_parent().emitEquip(item)
	
	
	"""
		if left click RELEASED, force drag and drop
	"""
	if (ev.is_action_released("left_click")):
		self.accept_event()
		var item = self.getItem()
		if (item != null):
			self.unsetItem()
			var preview = self.getDragPreview(item)
			self.call_deferred("force_drag", item, preview)


"""
	Returns a new Sprite with an item's icon, so we can se what we are dragging. 
	
	@param Item	_item	The item we need to generate the preview for. If it's null,
						get the current item.
	
	@return Control		A control node with a Sprite child, containing the preview.
						Control is used because the drag preview needs to be a Control node (or a child of Control)
"""
func getDragPreview(item = null):
	if (item == null):
		item = self.getItem()
	
	if (item != null):
		var preview = Control.new()
		var sprite = Sprite.new()
		sprite.set_texture(item.icon)
		preview.add_child(sprite)
		
		return preview
	
	return null


"""
	Unsets the current item and starts the drag-and-drop flow.
	
	@param Vector2 _pos	The position clicked
	
	@return Item		The item we want to drag
"""
func get_drag_data(pos):
	var item = self.getItem()
	var preview = self.getDragPreview()
	self.set_drag_preview(preview)
	self.unsetItem()
	return item


"""
	Checks whether we can drop the item on the current slot.
	If the item is of class Item, then return true. Else return false
	
	@param Vector2	_pos	The position clicked
	@param Variant	_item	The dropped data
	
	@return book			True if we can drop the item here, false otherwise
"""
func can_drop_data(pos, data):
	if (data is Item):
		return true
	return false


"""
	Drop an item on the current slot. If the slot is already occupied, swap them.
	
	@param Vector2	_pos	The click/drop position
	@param Item		_item	The item to drop
	
	@return void
"""
func drop_data(_pos, _item):
	if(Input.is_action_pressed("left_click")):
		self.call_deferred("force_drag", _item, self.getDragPreview(_item))
	else:
		var oldItem = self.getItem()
		if (oldItem == null):
			self.setItem(_item)
		else:
			emit_signal("swapItem", _item)


"""
	Swaps the item currently occupying the slot with another one, and forces drag-and-drop on the current one
	 
	@param Item item	The item which to swap with the one currently on the slot
	
	@return void
"""
func swapItem(item):
	var oldItem = getItem()
	self.unsetItem()
	self.setItem(item)
	var preview	= self.getDragPreview(oldItem)
	self.force_drag(oldItem, preview)