Add wxFontEnumerator::InvalidateCache()

This is necessary to recognize new fonts, for example those added using
AddPrivateFont(), as being valid: otherwise they were not found in the
cache and couldn't be used in wxGTK.

include/wx/fontenum.h

@@ -74,6 +74,11 @@ public:
     // in the user's system
     static bool IsValidFacename(const wxString &str);
 
+    // Invalidate cache used by some of the methods of this class internally.
+    // This should be called if the list of the fonts available on the system
+    // changes, for whatever reason.
+    static void InvalidateCache();
+
 private:
 #ifdef wxHAS_UTF8_FONTS
     // helper for ports that only use UTF-8 encoding natively

interface/wx/fontenum.h

@@ -73,6 +73,17 @@ public:
     */
     static bool IsValidFacename(const wxString& facename);
 
+    /**
+        Invalidate cache used by some of the methods of this class internally.
+
+        This method should be called if the list of the fonts available on the
+        system changes, for whatever reason. In particular, it is called
+        automatically by wxFont::AddPrivateFont().
+
+        @since 3.1.1
+     */
+    static void InvalidateCache();
+
     /**
         Called by EnumerateFacenames() for each match.
 

src/common/fontenumcmn.cpp

@@ -127,6 +127,12 @@ bool wxFontEnumerator::IsValidFacename(const wxString &facename)
     return true;
 }
 
+/* static */
+void wxFontEnumerator::InvalidateCache()
+{
+    gs_allFacenames.clear();
+}
+
 #ifdef wxHAS_UTF8_FONTS
 bool wxFontEnumerator::EnumerateEncodingsUTF8(const wxString& facename)
 {