Add the tgrid::swap_child() function.

src/gui/widgets/grid.cpp

@@ -110,6 +110,44 @@ void tgrid::set_child(twidget* widget, const unsigned row,
 	clear_cache();
 }
 
+twidget* tgrid::swap_child(
+		const std::string& id, twidget* widget, const bool recurse)
+{
+	assert(widget);
+
+	foreach(tchild& child, children_) {
+		if(child.id() != id) {
+
+			if(recurse) {
+				// decent in the nested grids.
+				tgrid* grid = dynamic_cast<tgrid*>(child.widget());
+				if(grid) {
+
+					twidget* old = grid->swap_child(id, widget, true);
+					if(old) {
+						return old;
+					}
+				}
+			}
+
+			continue;
+		}
+
+		// When find the widget there should be a widget.
+		twidget* old = child.widget();
+		assert(old);
+		old->set_parent(NULL);
+
+		widget->set_parent(this);
+		child.set_widget(widget);
+		child.set_id(widget->id());
+
+		return old;
+	}
+
+	return NULL;
+}
+
 void tgrid::remove_child(const unsigned row, const unsigned col)
 {
 	assert(row < rows_ && col < cols_);

src/gui/widgets/grid.hpp

@@ -113,6 +113,23 @@ public:
 	void set_child(twidget* widget, const unsigned row, 
 		const unsigned col, const unsigned flags, const unsigned border_size);
 
+	/**
+	 * Exchangs a child in the grid.
+	 *
+	 * It replaced the child with a certain id with the new widget but doesn't
+	 * touch the other settings of the child.
+	 *
+	 * @param id                  The id of the widget to free.
+	 * @param widget              The widget to put in the grid.
+	 * @parem recurse             Do we want to decent into the child grids.
+	 *
+	 * returns                    The widget which got removed (the parent of
+	 *                            the widget is cleared). If no widget found
+	 *                            and thus not replace NULL will returned.
+	 */
+	twidget* swap_child(
+		const std::string& id, twidget* widget, const bool recurse);
+
 	/**
 	 * Removes and frees a widget in a cell.
 	 *