This morning I’m was working on a grid that has a GridSplitter to split the panes, but needed a quick way to collapse the left side to get it out of the way – and when finished, restore it to its previous size.  Something like the following scenario:

The solution for that is trivially simple:

        DateTime lastClicked;
        GridLength cachedColumnWidth;
        void GridSplitter_MouseLeftButtonUp(
          object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            //The Poor Man's DoubleClick:
            if (DateTime.Now.Subtract(lastClicked).TotalMilliseconds < 500)
            {
                GridSplitter splitter = sender as GridSplitter;
                //What column is it in?
                int colIndex = (int)splitter.GetValue(Grid.ColumnProperty);
                //And what grid are we talking about?
                Grid grid = splitter.Parent as Grid;
                Debug.Assert(grid.ColumnDefinitions.Count > 0);
                //Cool...now look at the column definition:
                GridLength gridLength = grid.ColumnDefinitions[colIndex].Width;
                //In order to see if we've already slammed the splitter up against the side:
                GridLength splitterWidth = new GridLength(splitter.Width);
                if (gridLength.Equals(splitterWidth))
                {
                    //Already collapsed..restore:
                    grid.ColumnDefinitions[colIndex].Width = cachedColumnWidth;
                }else{
                    //Collapse the column:
                    cachedColumnWidth = gridLength;
                    grid.ColumnDefinitions[colIndex].Width = splitterWidth;
                }
            }
            lastClicked = DateTime.Now;
        }

Links:

http://downloads.xact-solutions.com/Silverlight/Posts/100125b/XAct.Studies.GridSplitterCollapseEx.xap