Initialize atoms used in wxGTK wxDataObject on demand

This allows to avoid having to call PrepareFormats() manually which was
not only verbose, but also error-prone as proved by the fact that
wxURLDataObject used wxTextURIListDataObject which used g_fileAtom in
its ctor without calling PrepareFormats() first and meant that this
class didn't work correctly unless some other wxDataObject had been
created before it.

include/wx/gtk/dataform.h

@@ -70,8 +70,6 @@ private:
 
     wxDataFormatId   m_type;
     NativeFormat     m_format;
-
-    void PrepareFormats();
 };
 
 #endif // _WX_GTK_DATAFORM_H

src/gtk/clipbrd.cpp

@@ -44,7 +44,8 @@ typedef wxScopedArray<wxDataFormat> wxDataFormatArray;
 static GdkAtom  g_targetsAtom     = nullptr;
 static GdkAtom  g_timestampAtom   = nullptr;
 
-extern GdkAtom g_altTextAtom;
+// This is defined in src/gtk/dataobj.cpp.
+extern GdkAtom wxGetAltTextAtom();
 
 // the trace mask we use with wxLogTrace() - call
 // wxLog::AddTraceMask(TRACE_CLIPBOARD) to enable the trace messages from here
@@ -304,7 +305,7 @@ selection_handler( GtkWidget *WXUNUSED(widget),
     if ( !size )
         return;
 
-    wxLogTrace(TRACE_CLIPBOARD, "Valid clipboard data found");
+    wxLogTrace(TRACE_CLIPBOARD, "Valid clipboard data of size %d found", size);
 
     wxCharBuffer buf(size - 1); // it adds 1 internally (for NUL)
 
@@ -337,16 +338,18 @@ void wxClipboard::GTKOnSelectionReceived(const GtkSelectionData& sel)
 {
     wxCHECK_RET( m_receivedData, wxT("should be inside GetData()") );
 
-    const wxDataFormat format(gtk_selection_data_get_target(const_cast<GtkSelectionData*>(&sel)));
-    wxLogTrace(TRACE_CLIPBOARD, wxT("Received selection %s"),
-               format.GetId());
+    GtkSelectionData* const gsel = const_cast<GtkSelectionData*>(&sel);
+
+    const wxDataFormat format(gtk_selection_data_get_target(gsel));
+    wxLogTrace(TRACE_CLIPBOARD, wxT("Received selection %s, len=%d"),
+               format.GetId(), gtk_selection_data_get_length(gsel));
 
     if ( !m_receivedData->IsSupportedFormat(format, wxDataObject::Set) )
         return;
 
     m_receivedData->SetData(format,
-        gtk_selection_data_get_length(const_cast<GtkSelectionData*>(&sel)),
-        gtk_selection_data_get_data(const_cast<GtkSelectionData*>(&sel)));
+        gtk_selection_data_get_length(gsel),
+        gtk_selection_data_get_data(gsel));
     m_formatSupported = true;
 }
 
@@ -688,7 +691,7 @@ bool wxClipboard::IsSupported( const wxDataFormat& format )
     if ( format == wxDF_UNICODETEXT )
     {
         // also with plain STRING format
-        return DoIsSupported(g_altTextAtom);
+        return DoIsSupported(wxGetAltTextAtom());
     }
 
     return false;

src/gtk/dataobj.cpp

@@ -25,14 +25,48 @@
 #include "wx/gtk/private.h"
 
 //-------------------------------------------------------------------------
-// global data
+// module data
 //-------------------------------------------------------------------------
 
-GdkAtom  g_textAtom        = nullptr;
-GdkAtom  g_altTextAtom     = nullptr;
-GdkAtom  g_pngAtom         = nullptr;
-GdkAtom  g_fileAtom        = nullptr;
-GdkAtom  g_htmlAtom        = nullptr;
+namespace
+{
+
+// Atom initialized on first access.
+//
+// Note that this is more than just an optimization, as we have to delay
+// calling gdk_atom_intern() until after GDK initialization.
+class wxGdkAtom
+{
+public:
+    // Name is literal, so we don't copy it but just store the pointer.
+    wxGdkAtom(const char* name) : m_name{name} {}
+
+    wxGdkAtom(const wxGdkAtom&) = delete;
+    wxGdkAtom& operator=(const wxGdkAtom&) = delete;
+
+    operator GdkAtom()
+    {
+        if ( !m_atom )
+            m_atom = gdk_atom_intern(m_name, FALSE);
+
+        return m_atom;
+    }
+
+private:
+    const char* const m_name;
+    GdkAtom m_atom = nullptr;
+};
+
+wxGdkAtom g_textAtom    {"UTF8_STRING"};
+wxGdkAtom g_altTextAtom {"STRING"};
+wxGdkAtom g_pngAtom     {"image/png"};
+wxGdkAtom g_fileAtom    {"text/uri-list"};
+wxGdkAtom g_htmlAtom    {"text/html"};
+
+} // anonymous namespace
+
+// This is used in src/gtk/clipbrd.cpp
+extern GdkAtom wxGetAltTextAtom() { return g_altTextAtom; }
 
 //-------------------------------------------------------------------------
 // wxDataFormat
@@ -40,40 +74,27 @@ GdkAtom  g_htmlAtom        = nullptr;
 
 wxDataFormat::wxDataFormat()
 {
-    // do *not* call PrepareFormats() from here for 2 reasons:
-    //
-    // 1. we will have time to do it later because some other Set function
-    //    must be called before we really need them
-    //
-    // 2. doing so prevents us from declaring global wxDataFormats because
-    //    calling PrepareFormats (and thus gdk_atom_intern) before GDK is
-    //    initialised will result in a crash
     m_type = wxDF_INVALID;
     m_format = (GdkAtom) nullptr;
 }
 
 wxDataFormat::wxDataFormat( wxDataFormatId type )
 {
-    PrepareFormats();
     SetType( type );
 }
 
 void wxDataFormat::InitFromString( const wxString &id )
 {
-    PrepareFormats();
     SetId( id );
 }
 
 wxDataFormat::wxDataFormat( NativeFormat format )
 {
-    PrepareFormats();
     SetId( format );
 }
 
 void wxDataFormat::SetType( wxDataFormatId type )
 {
-    PrepareFormats();
-
     m_type = type;
 
     if (m_type == wxDF_UNICODETEXT)
@@ -108,7 +129,6 @@ wxString wxDataFormat::GetId() const
 
 void wxDataFormat::SetId( NativeFormat format )
 {
-    PrepareFormats();
     m_format = format;
 
     if (m_format == g_textAtom)
@@ -131,33 +151,10 @@ void wxDataFormat::SetId( NativeFormat format )
 
 void wxDataFormat::SetId( const wxString& id )
 {
-    PrepareFormats();
     m_type = wxDF_PRIVATE;
     m_format = gdk_atom_intern( id.ToAscii(), FALSE );
 }
 
-void wxDataFormat::PrepareFormats()
-{
-    // VZ: GNOME included in RedHat 6.1 uses the MIME types below and not the
-    //     atoms STRING and file:ALL as the old code was, but normal X apps
-    //     use STRING for text selection when transferring the data via
-    //     clipboard, for example, so do use STRING for now (GNOME apps will
-    //     probably support STRING as well for compatibility anyhow), but use
-    //     text/uri-list for file dnd because compatibility is not important
-    //     here (with whom?)
-    if (!g_textAtom)
-    {
-        g_textAtom = gdk_atom_intern( "UTF8_STRING", FALSE );
-        g_altTextAtom = gdk_atom_intern( "STRING", FALSE );
-    }
-    if (!g_pngAtom)
-        g_pngAtom = gdk_atom_intern( "image/png", FALSE );
-    if (!g_fileAtom)
-        g_fileAtom = gdk_atom_intern( "text/uri-list", FALSE );
-    if (!g_htmlAtom)
-        g_htmlAtom = gdk_atom_intern( "text/html", FALSE );
-}
-
 //-------------------------------------------------------------------------
 // wxDataObject
 //-------------------------------------------------------------------------