fix bug that listbox incorrectly performs scroll_down/up

source/gui/widgets/listbox.cpp

@@ -1273,6 +1273,7 @@ namespace nana
 					}
 					
 					//Backward
+					n = -n;
 					dpos = pos;
 					if (good(dpos.cat))
 					{
@@ -1618,7 +1619,7 @@ namespace nana
 				}
 
 				/// return absolute positions, no relative to display
-				index_pairs pick_items(bool for_selection) const
+				index_pairs pick_items(bool for_selection, bool find_first = false) const
 				{
 					index_pairs results;
 					index_pair id;
@@ -1629,7 +1630,11 @@ namespace nana
 						for (auto & m : cat.items)
 						{
 							if (for_selection ? m.flags.selected : m.flags.checked)
+							{
 								results.push_back(id);  // absolute positions, no relative to display
+								if (find_first)
+									return results;
+							}
 							++id.item;
 						}
 						++id.cat;
@@ -4336,8 +4341,9 @@ namespace nana
 
 				void trigger::key_press(graph_reference graph, const arg_keyboard& arg)
 				{
+					auto & list = essence_->lister;
 					// Exit if list is empty
-					if (essence_->lister.first().empty())
+					if (list.first().empty())
 						return;
 
 					bool upward = false;
@@ -4347,12 +4353,12 @@ namespace nana
 					case keyboard::os_arrow_up:
 						upward = true;
 					case keyboard::os_arrow_down:
-						essence_->lister.move_select(upward, !arg.shift, true);
+						list.move_select(upward, !arg.shift, true);
 						break;
 					case L' ':
 						{
 							index_pairs s;
-							bool ck = ! essence_->lister.item_selected_all_checked(s);
+							bool ck = ! list.item_selected_all_checked(s);
 							for(auto i : s)
 								item_proxy(essence_, i).check(ck);
 						}
@@ -4361,30 +4367,69 @@ namespace nana
 						upward = true;
 					case keyboard::os_pagedown:
 						{
-							//Turns page, then returns if no change occurs
+							auto const item_px = essence_->item_height();
-							if (!essence_->content_view->turn_page(!upward, false))
+							auto picked_items = list.pick_items(true, true);
-								return;
+							index_pair init_idx = (picked_items.empty() ? list.first() : picked_items[0]);
 
 							essence_->lister.select_for_all(false);
 
-							auto idx = essence_->first_display();
+							//Get the pixels between the init item and top edge or bottom edge
+							auto logic_top = static_cast<int>(list.distance(list.first(), init_idx) * item_px);
 
-							if (!upward)
+							auto const screen_top = essence_->content_view->origin().y;
-								idx = essence_->lister.advance(idx, static_cast<int>(essence_->count_of_exposed(false)) - 1);
+							auto const screen_bottom = screen_top + essence_->content_view->view_area().height;
+							index_pair target_idx;
 
-							if (!idx.is_category())
+							//Check if it scrolls in current screen window
-								item_proxy::from_display(essence_, idx).select(true);
+							//condition: top of target item is not less than top edge of content view and
-							else if (!essence_->lister.single_status(true))	//not selected
+							//the bottom of target item is not greater than bottom edge of content view.
-								essence_->lister.cat_status(idx.cat, true, true);
+							if ((screen_top + item_px <= logic_top) && (logic_top + item_px + item_px <= screen_bottom))
+							{
+								int offset = (static_cast<int>(upward ? screen_top : screen_bottom - item_px) - logic_top) / static_cast<int>(item_px);
+								target_idx = list.advance(init_idx, offset);
+							}
+							else
+							{
+								//turn page
+								auto page_item_count = (std::max)(1, static_cast<int>(essence_->count_of_exposed(false)));
 
-							break;
+								auto origin = essence_->content_view->origin();
+								if (upward)
+								{
+									target_idx = list.advance(init_idx, -page_item_count);
+									if (target_idx.empty())
+										target_idx = list.first();
+
+									origin.y = list.distance(list.first(), target_idx) * item_px;
+								}
+								else
+								{
+									target_idx = list.advance(init_idx, page_item_count);
+									if (target_idx.empty())
+										target_idx = list.last();
+
+									origin.y = list.distance(list.first(), target_idx) * item_px + item_px;
+									if (origin.y >= (screen_bottom - screen_top))
+										origin.y -= (screen_bottom - screen_top);
+									else
+										origin.y = 0;
+								}
+
+								essence_->content_view->move_origin(origin - essence_->content_view->origin());
+							}
+						
+							if (!target_idx.is_category())
+								item_proxy::from_display(essence_, target_idx).select(true);
+							else if (!list.single_status(true))	//not selected
+								list.cat_status(target_idx.cat, true, true);
 						}
+						break;
 					case keyboard::os_home:
 					case keyboard::os_end:
 						{
-							essence_->lister.select_for_all(false);
+							list.select_for_all(false);
 
-							auto pos = (keyboard::os_home == arg.key ? essence_->lister.first() : essence_->lister.last());
+							auto pos = (keyboard::os_home == arg.key ? list.first() : list.last());
 							if (!pos.empty())
 							{
 								//When the pos indicates an empty category, then search forwards/backwards(depending on arg.key whether it is Home or End) for a non empty category.
@@ -4393,9 +4438,9 @@ namespace nana
 								{
 									if (keyboard::os_home == arg.key)
 									{
-										while (0 == essence_->lister.size_item(pos.cat))
+										while (0 == list.size_item(pos.cat))
 										{
-											if (++pos.cat >= essence_->lister.cat_container().size())
+											if (++pos.cat >= list.cat_container().size())
 											{
 												pos = index_pair{ npos, npos };
 												break;
@@ -4404,7 +4449,7 @@ namespace nana
 									}
 									else
 									{
-										while (0 == essence_->lister.size_item(pos.cat))
+										while (0 == list.size_item(pos.cat))
 										{
 											if (pos.cat-- == 0)
 											{
@@ -4416,7 +4461,7 @@ namespace nana
 
 									if (!pos.empty())
 									{
-										if (essence_->lister.expand(pos.cat))
+										if (list.expand(pos.cat))
 											pos.item = 0;
 									}
 								}
@@ -4425,8 +4470,8 @@ namespace nana
 								{
 									if (pos.is_category())
 									{
-										if (!essence_->lister.single_status(true)) //multiple selection is not enabled
+										if (!list.single_status(true)) //multiple selection is not enabled
-											essence_->lister.cat_status(pos.cat, true, true);
+											list.cat_status(pos.cat, true, true);
 									}
 									else
 										item_proxy::from_display(essence_, pos).select(true);

source/gui/widgets/scroll.cpp

@@ -1,7 +1,7 @@
 /*
  *	A Scroll Implementation
  *	Nana C++ Library(http://www.nanapro.org)
- *	Copyright(C) 2003-2014 Jinhao(cnjinhao@hotmail.com)
+ *	Copyright(C) 2003-2018 Jinhao(cnjinhao@hotmail.com)
  *
  *	Distributed under the Boost Software License, Version 1.0. 
  *	(See accompanying file LICENSE_1_0.txt or copy at 
@@ -20,9 +20,15 @@ namespace nana
 		namespace scroll
 		{
 		//struct metrics_type
-			metrics_type::metrics_type()
+			metrics_type::metrics_type():
-				:peak(1), range(1), step(1), value(0),
+				peak(1),
-				what(buttons::none), pressed(false), scroll_length(0), scroll_pos(0)
+				range(1),
+				step(1),
+				value(0),
+				what(buttons::none),
+				pressed(false),
+				scroll_length(0),
+				scroll_pos(0)
 			{}
 		//end struct metrics_type