Merging column headers in ultragrid

Hi,

The element should always have it's Rect set before the BeforeCreateChildElements fires. But I don't think the approach you took here is quite right, anyway. It's probably not a good idea to move the parent element.

Your code is also making the assumption that you wlil always be using the main column's HeaderUIElement, but that will not work if that column is scrolled out of view.

Here's a better way:


public class ColHeaderSpannerCreationFilter : IUIElementCreationFilter
    {
        private UltraGridColumn Column1 { get; set; }
        private UltraGridColumn Column2 { get; set; }        

        public ColHeaderSpannerCreationFilter(UltraGridColumn column1, UltraGridColumn column2)
        {            
            this.Column1 = column1;
            this.Column2 = column2;
        }

        public void AfterCreateChildElements(UIElement parent)
        {
            if (parent is BandHeadersUIElement)
            {
                HeaderUIElement headerElement1 = parent.GetDescendant(typeof(HeaderUIElement), this.Column1) as HeaderUIElement;
                HeaderUIElement headerElement2 = parent.GetDescendant(typeof(HeaderUIElement), this.Column2) as HeaderUIElement;

                // If boith of the elements are scrolled out of view, then do nothing. 
                if (headerElement1 == null &&
                    headerElement2 == null)
                {
                    return;
                }

                UIElement elementToExtend = headerElement1 != null ? headerElement1 : headerElement2;
                UIElement elementToRemove = headerElement1 != null ? headerElement2 : headerElement1;

                // Make one header element fill the space of both column headers. 
                if (elementToRemove != null)
                {
                    elementToExtend.Rect = Rectangle.Union(elementToExtend.Rect, elementToRemove.Rect);

                    // Remove the other element
                    parent.ChildElements.Remove(elementToRemove);
                }
            }
        }

        public bool BeforeCreateChildElements(UIElement parent)
        {
            //Return false to let the grid know we did not handle the event. 
            return false;
        }
    }

This works pretty well, but there is a small problem when you scroll the column(s) out of view and then back into view, because the grid doesn't know it has to dirty both header elements. So you just have to tell the grid to dirty the headers when it scrolls. Like so:


        private void ultraGrid1_BeforeColRegionScroll(object sender, BeforeColRegionScrollEventArgs e)
        {
            UltraGrid grid = (UltraGrid)sender;
            UIElement bandHeadersUIElement = grid.DisplayLayout.UIElement.GetDescendant(typeof(BandHeadersUIElement));
            if (bandHeadersUIElement != null)
                bandHeadersUIElement.DirtyChildElements(true);
        }