optimize UIWidget for largers NPC trades

modules/game_npctrade/npctrade.lua

@@ -148,7 +148,7 @@ local function refreshTradeItems()
   for key,item in pairs(currentTradeItems) do
     local itemBox = createWidget('NPCItemBox', itemsPanel)
     itemBox.item = item
-    
+
     local name = item.name
     local weight = string.format('%.2f', item.weight) .. ' ' .. WEIGHT_UNIT
     local price = item.price .. ' ' .. CURRENCY

modules/game_npctrade/npctrade.otui

@@ -19,7 +19,7 @@ NPCItemBox < UICheckBox
     anchors.horizontalCenter: parent.horizontalCenter
     margin-top: 5
 
-  $checked:    
+  $checked:
     border-color: #ffffff
 
   $hover !checked:

src/framework/ui/uiwidget.cpp

@@ -133,6 +133,8 @@ void UIWidget::addChild(const UIWidgetPtr& child)
         return;
     }
 
+    UIWidgetPtr oldLastChild = getLastChild();
+
     m_children.push_back(child);
     child->setParent(asUIWidget());
 
@@ -145,7 +147,12 @@ void UIWidget::addChild(const UIWidgetPtr& child)
 
     // update new child states
     child->updateStates();
-    updateChildrenIndexStates();
+
+    // update old child index states
+    if(oldLastChild) {
+        oldLastChild->updateState(Fw::MiddleState);
+        oldLastChild->updateState(Fw::LastState);
+    }
 
     g_ui.onWidgetAppear(child);
 }
@@ -714,8 +721,15 @@ void UIWidget::destroyChildren()
     if(layout)
         layout->disableUpdates();
 
-    while(!m_children.empty())
-        m_children[0]->destroy();
+    m_focusedChild = nullptr;
+    m_lockedChildren.clear();
+    while(!m_children.empty()) {
+        UIWidgetPtr child = m_children.front();
+        m_children.pop_front();
+        child->setParent(nullptr);
+        m_layout->removeWidget(child);
+        child->destroy();
+    }
 
     layout->enableUpdates();
 }