Add wxPersistentComboBox for saving and restoring combobox items

This allows to preserve the history of user input.

include/wx/persist/combobox.h

@@ -0,0 +1,99 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/persist/combobox.h
+// Purpose:     Persistence adapter for wxComboBox
+// Author:      Vadim Zeitlin
+// Created:     2020-11-19
+// Copyright:   (c) 2020 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PERSIST_COMBOBOX_H_
+#define _WX_PERSIST_COMBOBOX_H_
+
+#include "wx/persist/window.h"
+
+#include "wx/combobox.h"
+
+#define wxPERSIST_COMBOBOX_KIND wxASCII_STR("Combobox")
+
+// Stores semicolon-separated list of combobox entries (real semicolons are
+// escaped using backslash), i.e. "first;second;...".
+#define wxPERSIST_COMBOBOX_ITEMS wxASCII_STR("Items")
+
+#define wxPERSIST_COMBOBOX_ITEMS_SEP ';'
+
+// ----------------------------------------------------------------------------
+// wxPersistentComboBox: supports saving/restoring combobox items
+// ----------------------------------------------------------------------------
+
+class wxPersistentComboBox : public wxPersistentWindow<wxComboBox>
+{
+public:
+    // The maximum number of items to save is currently hard-coded.
+    //
+    // Notice that we must have some limit, as otherwise the length of the
+    // items string in the config would be unbounded, which certainly wouldn't
+    // be a good idea.
+    enum { MaxSavedItemsCount = 10 };
+
+    explicit wxPersistentComboBox(wxComboBox* combobox)
+        : wxPersistentWindow<wxComboBox>(combobox)
+    {
+    }
+
+    virtual void Save() const wxOVERRIDE
+    {
+        const wxComboBox* const combobox = Get();
+
+        wxArrayString items = combobox->GetStrings();
+
+        const wxString value = combobox->GetValue();
+        if ( !value.empty() )
+        {
+            wxArrayString::iterator it;
+            for ( it = items.begin(); it != items.end(); ++it )
+            {
+                if ( *it == value )
+                {
+                    // There is no need to add the text of an item already
+                    // present in the combobox again, but do move it to the top
+                    // of it to indicate that it was the last one used.
+                    wxSwap(*items.begin(), *it);
+                    break;
+                }
+            }
+
+            if ( it == items.end() )
+            {
+                // This is a genuinely new item, so just insert it front.
+                items.insert(items.begin(), value);
+
+                if ( items.size() > MaxSavedItemsCount )
+                    items.erase(items.begin() + MaxSavedItemsCount, items.end());
+            }
+        }
+
+        SaveValue(wxPERSIST_COMBOBOX_ITEMS,
+                  wxJoin(items, wxPERSIST_COMBOBOX_ITEMS_SEP));
+    }
+
+    virtual bool Restore() wxOVERRIDE
+    {
+        wxString items;
+        if ( !RestoreValue(wxPERSIST_COMBOBOX_ITEMS, &items) )
+            return false;
+
+        Get()->Set(wxSplit(items, wxPERSIST_COMBOBOX_ITEMS_SEP));
+
+        return true;
+    }
+
+    virtual wxString GetKind() const wxOVERRIDE { return wxPERSIST_COMBOBOX_KIND; }
+};
+
+inline wxPersistentObject *wxCreatePersistentObject(wxComboBox* combobox)
+{
+    return new wxPersistentComboBox(combobox);
+}
+
+#endif // _WX_PERSIST_COMBOBOX_H_