Drag and drop location indicator | Infragistics Forums

There is code in the ItemDropHighlightUIElement class that checks to make sure an internal drag is in progress, which in your case it won't be, so recommending you use that was a bad idea.

The following code sample demonstrates how to implement the IUIElementCreationFilter interface to display a drop indicator when something is being dragged over the ExplorerBar:

#region ItemDragIndicatorCreationFilter
/// <summary>
/// IUIElementCreationFilter implementation which displays an item drop indicator
/// when a drag operation which originated from a different control is in progress
/// and the cursor is positioned over an ItemUIElement.
/// </summary>
public class ItemDragIndicatorCreationFilter : IUIElementCreationFilter, IDisposable
{
    #region Member variables
    private UltraExplorerBar explorerBar = null;
    private bool isDragging = false;
    #endregion Member variables

    #region Constructor
    /// <summary>
    /// Creates a new instance of the class.
    /// </summary>
    public ItemDragIndicatorCreationFilter( UltraExplorerBar explorerBar )
    {
        this.explorerBar = explorerBar;

        // Hook the DragEnter, DragLeave, and DragOver events so we
        // can listen for things being dragged over the ExplorerBar.
        this.HookDragEvents( true );
    }

#endregion Constructor

    #region HookDragEvents
    private void HookDragEvents( bool hook )
    {
        if ( this.explorerBar == null )
            return;

        if ( hook )
        {
            this.explorerBar.DragEnter += new DragEventHandler(explorerBar_DragEnter);
            this.explorerBar.DragLeave += new EventHandler(explorerBar_DragLeave);
            this.explorerBar.DragOver += new DragEventHandler(explorerBar_DragOver);
        }
        else
        {
            this.explorerBar.DragEnter -= new DragEventHandler(explorerBar_DragEnter);
            this.explorerBar.DragLeave -= new EventHandler(explorerBar_DragLeave);
            this.explorerBar.DragOver -= new DragEventHandler(explorerBar_DragOver);
        }
    }
    #endregion HookDragEvents

    #region Drag events
    void explorerBar_DragLeave(object sender, EventArgs e)
    {
        this.isDragging = false;        }

    void explorerBar_DragEnter(object sender, DragEventArgs e)
    {
        this.isDragging = true;
    }
    private void explorerBar_DragOver(object sender, DragEventArgs e)
    {
        this.explorerBar.UIElement.DirtyChildElements( true );
    }
    #endregion Drag events

#region IUIElementCreationFilter implementation

    void IUIElementCreationFilter.AfterCreateChildElements(UIElement parent)
    {
        if ( this.isDragging == false )
            return;

ItemAreaInnerUIElement itemAreaElement = parent as ItemAreaInnerUIElement;

        if ( itemAreaElement != null )
        {
            // Get the current mouse position in client coordinates
            Point cursorPos = this.explorerBar.PointToClient( Control.MousePosition );

            // Iterate the child elements and add the drop indicator
            // when we hit the drop target item
            UIElementsCollection childElements = itemAreaElement.ChildElements;

            foreach( UIElement element in childElements )
            {
                // If this element is not an ItemUIElement, skip it
                ItemUIElement itemElement = element as ItemUIElement;
                if ( itemElement == null )
                    continue;

                // Hit test each item element to see if the cursor is currently over it
                Rectangle itemElementRect = itemElement.Rect;
                if ( itemElementRect.Contains(cursorPos) )
                {
                    // Create the DropHighlightElement
                    DropHighlightElement dropHighlightElement = new DropHighlightElement(itemAreaElement);

                    // Calculate the Rect and set it (note that this is simplified for the sake of brevity)
                    Rectangle rect = itemElementRect;
                    rect.Height = 5;
                    rect.Y = itemElementRect.Top - 5;
                    dropHighlightElement.Rect = rect;

                    // Add it to the ItemAreaInnerUIElement's ChildElements collection
                    childElements.Add( dropHighlightElement );
                    break;
                }
            }
        }
    }

    bool IUIElementCreationFilter.BeforeCreateChildElements(UIElement parent)
    {
        return false;
    }

#endregion IUIElementCreationFilter implementation

#region IDisposable Members

    void IDisposable.Dispose()
    {
        this.HookDragEvents( false );
        this.explorerBar = null;
    }

#endregion

    #region DropHighlightElement class
    public class DropHighlightElement : UIElement
    {
        public DropHighlightElement( UIElement parent ) : base( parent ){}

        protected override void DrawBackColor(ref UIElementDrawParams drawParams)
        {
            // Do nothing so no background is drawn
        }

        protected override void DrawForeground(ref UIElementDrawParams drawParams)
        {
            using( SolidBrush brush = new SolidBrush(Color.Red) )
            {
                // Note that this is simplified for the sake of brevity
                drawParams.Graphics.FillRectangle( brush, this.Rect );
            }
        }
    }
    #endregion DropHighlightElement class
}
#endregion ItemDragIndicatorCreationFilter