FIX: back up the selected printer in prepare page

jira: none
Change-Id: Ibd163f78c4ce911a88459ecca96660ed4aa68ab2
(cherry picked from commit 392e8e18915d0db26ca8a3840d5783cc81cd1c1c)

src/slic3r/GUI/Plater.cpp

@@ -2773,6 +2773,11 @@ void Sidebar::update_dynamic_filament_list()
     dynamic_filament_list_1_based.update();
 }
 
+PlaterPresetComboBox* Sidebar::printer_combox()
+{
+    return p->combo_printer;
+}
+
 ObjectList* Sidebar::obj_list()
 {
     // BBS

src/slic3r/GUI/Plater.hpp

@@ -174,6 +174,7 @@ public:
     void show_SEMM_buttons(bool bshow);
     void update_dynamic_filament_list();
 
+    PlaterPresetComboBox *  printer_combox();
     ObjectList*             obj_list();
     ObjectSettings*         obj_settings();
     ObjectLayers*           obj_layers();

src/slic3r/GUI/PresetComboBoxes.cpp

@@ -180,7 +180,7 @@ void PresetComboBox::invalidate_selection()
 
 void PresetComboBox::validate_selection(bool predicate/*=false*/)
 {
-    if (predicate ||
+    if (predicate &&
         // just in case: mark m_last_selected as a first added element
         m_last_selected == INT_MAX)
         m_last_selected = GetCount() - 1;
@@ -310,30 +310,37 @@ wxString PresetComboBox::get_preset_item_name(unsigned int index)
     if (m_type == Preset::TYPE_PRINTER) {
         int idx = selected_connected_printer();
         if (idx < 0) {
+            m_selected_dev_id.clear();
             return GetString(index);
         }
         else {
             DeviceManager *dev = Slic3r::GUI::wxGetApp().getDeviceManager();
             if (!dev) {
                 assert(false);
+                m_selected_dev_id.clear();
                 return GetString(index);
             }
 
             std::map<std::string, MachineObject *> machine_list = dev->get_my_machine_list();
             if (machine_list.empty()) {
                 assert(false);
+                m_selected_dev_id.clear();
                 return GetString(index);
             }
 
             auto iter = machine_list.begin();
             std::advance(iter, idx);
-            Preset* machine_preset = get_printer_preset(iter->second);
+            if (iter != machine_list.end()) {
-            if (machine_preset) {
+                m_selected_dev_id = *iter;
-                return from_u8(machine_preset->name);
+                Preset* machine_preset = get_printer_preset(iter->second);
+                if (machine_preset) {
+                    return from_u8(machine_preset->name);
+                }
             }
         }
     }
 
+    m_selected_dev_id.clear();
     return GetString(index);
 }
 
@@ -447,6 +454,7 @@ void PresetComboBox::add_connected_printers(std::string selected, bool alias_nam
         boost::replace_all(printer_model, "Bambu Lab ", "");
         auto text = iter->second->dev_name + " (" + printer_model + ")";
         int  item_id = Append(from_u8(text), wxNullBitmap, &m_first_printer_idx + std::distance(machine_list.begin(), iter));
+        validate_selection(m_selected_dev_id == iter->first);
     }
     m_last_printer_idx = GetCount();
 }

src/slic3r/GUI/PresetComboBoxes.hpp

@@ -77,6 +77,8 @@ public:
     void set_filament_idx(const int extr_idx) { m_filament_idx = extr_idx; }
     int  get_filament_idx() const { return m_filament_idx; }
 
+    std::string get_selected_dev_id() const { return m_selected_dev_id; }
+
     // BBS
     wxString get_tooltip(const Preset& preset);
 
@@ -132,6 +134,8 @@ protected:
     int m_first_printer_idx = 0;
     int m_last_printer_idx  = 0;
 
+    std::string              m_selected_dev_id;
+
     PrinterTechnology printer_technology {ptAny};
 
     void invalidate_selection();