add a param to listbox::item_proxy's check/select

this new parameter is used to indicate whether to scroll the view to the
item if the item is not displayed on screen.

include/nana/gui/widgets/listbox.hpp

@@ -800,12 +800,31 @@ namespace nana
 				/// posible use: last_selected_display = last_selected.to_display().item; use with caution, it get invalidated after a sort()
 				index_pair to_display() const;
 
+				/// Determines whether the item is displayed on the screen
+				bool displayed() const;
+
 				bool empty() const;
 
-				item_proxy & check(bool ck);
+				/// Checks/unchecks the item
+				/**
+				* @param chk Indicates whether to check or uncheck the item
+				* @param scroll_view Indicates whether to scroll the view to the item. It is ignored if the item is displayed.
+				* @return the reference of *this.
+				*/
+				item_proxy & check(bool chk, bool scroll_view = false);
+
+				/// Determines whether the item is checked
 				bool checked() const;
 
-				item_proxy & select(bool);
+				/// Selects/unselects the item
+				/**
+				 * @param sel Indicates whether to select or unselect the item
+				 * @param scroll_view Indicates whether to scroll the view to the item. It is ignored if the item is displayed.
+				 * @return the reference of *this.
+				 */
+				item_proxy & select(bool sel, bool scroll_view = false);
+
+				/// Determines whether he item is selected
 				bool selected() const;
 
 				item_proxy & bgcolor(const nana::color&);

source/gui/widgets/listbox.cpp

@@ -4506,12 +4506,28 @@ namespace nana
 					return ess_->lister.relative_pair(pos_);
 				}
 
+				bool item_proxy::displayed() const
+				{
+					if (!ess_->lister.get(pos_.cat)->expand)
+						return false;
+
+					auto pos = to_display();
+					if (ess_->scroll.offset_y_dpl > pos)
+						return false;
+
+					auto size = ess_->number_of_lister_items(false);
+
+					auto last = ess_->lister.advance(ess_->scroll.offset_y_dpl, size);
+
+					return (last > pos || last == pos);
+				}
+
 				bool item_proxy::empty() const
 				{
 					return !ess_;
 				}
 
-				item_proxy & item_proxy::check(bool ck)
+				item_proxy & item_proxy::check(bool ck, bool scroll_view)
 				{
 					internal_scope_guard lock;
 					auto & m = cat_->items.at(pos_.item);
@@ -4520,6 +4536,15 @@ namespace nana
 						m.flags.checked = ck;
 						ess_->lister.emit_checked(pos_);
 
+						if (scroll_view)
+						{
+							if (ess_->lister.get(pos_.cat)->expand)
+								ess_->lister.get(pos_.cat)->expand = false;
+
+							if (!this->displayed())
+								ess_->lister.scroll(pos_, !(ess_->scroll.offset_y_dpl > this->to_display()));
+						}
+
 						ess_->update();
 					}
 					return *this;
@@ -4531,14 +4556,15 @@ namespace nana
 				}
 
 				/// is ignored if no change (maybe set last_selected anyway??), but if change emit event, deselect others if need ans set/unset last_selected
-				item_proxy & item_proxy::select(bool s)
+				item_proxy & item_proxy::select(bool sel, bool scroll_view)
 				{
 					internal_scope_guard lock;
 
 					//pos_ never represents a category if this item_proxy is available.
 					auto & m = cat_->items.at(pos_.item);       // a ref to the real item
-					if(m.flags.selected == s) return *this;     // ignore if no change
+					if (m.flags.selected != sel)
-					m.flags.selected = s;                       // actually change selection
+					{
+						m.flags.selected = sel;                       // actually change selection
 
 						ess_->lister.emit_selected(this->pos_);
 
@@ -4550,7 +4576,17 @@ namespace nana
 						else if (ess_->lister.last_selected_abs == pos_)
 							ess_->lister.last_selected_abs.set_both(npos);
 
+						if (scroll_view)
+						{
+							if (ess_->lister.get(pos_.cat)->expand)
+								ess_->lister.get(pos_.cat)->expand = false;
+
+							if (!this->displayed())
+								ess_->lister.scroll(pos_, !(ess_->scroll.offset_y_dpl > this->to_display()));
+						}
+
 						ess_->update();
+					}
 					return *this;
 				}