void UpdateCurrentGroupSize()
		{
			var gsd = GroupSizeDefinitions;
			if (gsd == null || gsd.Count == 0)
			{
				mCurrentGroupSizeDefinition = null;
			}
			else
			{
				var iGS = IsCollapsed ? 0 : GroupSizeIndex;
				iGS = iGS < 0 ? 0 : iGS >= gsd.Count ? gsd.Count - 1 : iGS;
				mCurrentGroupSizeDefinition = gsd[iGS];

				int iItem = 0;
				for (int i = 0; i + iItem < Items.Count && i < mCurrentGroupSizeDefinition.ControlSizeDefinitions.Count; i++)
				{
					while (i + iItem < Items.Count)
					{
						var ic = Items[i + iItem] as IRibbonGroupControl;
						if (ic != null)
						{
							ic.ControlSizeDefinition = mCurrentGroupSizeDefinition.ControlSizeDefinitions[i];
							break;
						}
						else
						{
							iItem++;
						}
					}
				}
			}
		}
		void OnIsCollapsedChanged(bool OldValue, bool NewValue)
		{
			mCurrentGroupSizeDefinition = null;
		}